Webinar on 'Energy Efficiency: Retrofit in Traditional Buildings Policy and Research Update Part 1'

Energy Efficiency: Retrofit in Traditional Buildings Policy and Research Update – Part 1 

Speakers: Juliet Baillie, Nicholas Heath, Paul Baker and Harry Paticas 

Alice [00:07] And welcome. Hi, Juliet. 

Juliet [00:11] Thank you very much, Alice. Thanks for getting everyone set up and going. It's great to see so many people have joined – some familiar names to me and some that I don't know, so welcome, all. So thank you for joining us for today's session on energy efficiency and retrofit in traditional buildings. I am Juliet Bailey. I'm sector skills advisor at Historic England. 

Over the past few years, we've been delivering a programme of construction and heritage skills training activities as part of our major conservation-led regeneration project at Shrewsbury Flaxmill Maltings, and the heritage skills programme has been supported by the Andrew Lloyd Webber Foundation and the National Lottery Heritage Fund, and we're really grateful for their support and meaning that we can put this event on today. It was actually originally planned to take place in March of last year, but that was not possible for reasons that are probably quite obvious, so it's great to be able to take this event online and to bring it to a wider audience as well. So thank you again for joining us again today. 

So, Shrewsbury Flaxmill Maltings is not the subject of today's event, but if you would like to know more about the site, which includes the first iron-framed building in the world, which is pictured here on the screen, and if you would like to know more about the project that Historic England is leading, you can visit our web page, and also you might be interested to look at our webinar that took place last week if you didn't attend it. So I'll pop some links in a moment into the chat so that you can get access to those different things. 

So, today's event is under the barrier of Historic England's Technical Tuesdays webinar programme, and Shrewsbury Flaxmill Maltings was the subject of last week's webinar, and that recording is available online. It's about the project as a whole, but it actually does include some content that's sort of relevant to the things that we'll be talking about today, including the fact that we're having a ground-source heat pump as part of the project. 

So, we've split the original planned event across two sessions, and this afternoon's session – thank you for joining us – and also next Thursday-- sorry next Tuesday, 2nd February, and today we will hear from three speakers. They are Nicholas Heath, from the Sustainable Traditional Buildings Alliance, Paul Baker, who is a building physics consultant, and Harry Paticas, who is from Retrofit Action for tomorrow. We've factored in some time for a couple of comfort breaks to get away from the screen as we're aware that we're all spending time looking at screens these days, so you can obviously have a chance to grab a cup of tea, stretch your legs a little bit. And then next week's session, we will have another presentation from Nicholas Heath and one from Sarah Kahn of Roger Mears Architects, and we'll also have a panel discussion with all the speakers who've been involved. 

If you have any questions throughout the session, please do put them in the chat box on the left-hand side of the screen, and if you put a Q before it, that would be really helpful as that lets us know that it's a question so we can identify them easily. And as I said, we'll be putting links to kind of relevant bits of information or resources that you might want to access, including things like these two resources, which is Historic England's package of guidance on energy efficiency and the STBA Responsible Retrofit Wheel. So I now want to hand over to Morwenna Slade, who's recently joined Historic England as head of historic building climate change reduction and who will be chairing today's session, so thank you very much for joining us, and I'll hand over to Morwenna. 

Morwenna [04:23] Thank you, Juliet, and thanks, everybody, for joining us this session. As Juliet says, it's been a long time in the planning, I think, and I have to say that one of the positive things about this last year, although we've had to look quite hard for them, has been the sheer quantity of excellent CPT opportunities that lots of organisations have been providing, but specifically the Technical Tuesdays have been a real winner for myself, and if you haven't partaken of those, they are available and I do recommend them for a bit of a geek out and a cup of coffee. 

It's also meant that moving everything online has made it much more accessible for many people to participate in discussions and debate around issues like today's subject, and I think that's a real opportunity. As Juliet said, I've recently joined Historic England in the new role of specifically looking at climate change adaptation in the technical conservation team. 

So kind of a catch-all but before we get onto our main speakers, I'm going to kind of give an overview of where we are and how I see things. As I'm sure many of you are aware, buildings are the third largest carbon-emitting sector in the UK today after transport and industry, and we're not on track to meet the UK's 2050 net zero target. This is a nice little diagram produced by the CCC. Building sector is in orange in the middle, and you can see we haven't really achieved much overall since 1990. It's about a 17% reduction in emissions, and most of those are down to reductions in other sectors that are associated, such as the power sector. 

The UK has around 27 million existing domestic buildings, around 2 million non-domestic, and we have a replacement rate of only about 1% a year, so our net zero goals aren't going to achieve by building new things, and we have to improve the performance and potential of all the buildings that we have. The scale of this task is enormous. Within that 27 million buildings, we have the oldest homes in Europe, and about 25% of this is built pre-1919, so of traditional construction. In the face of retrofit and energy efficiency measures, driven by climate change targets and government policy, there is a need to be balanced, sensitive and take a sustainable approach that is really crucial. But we have to understand that inaction is not an option. Just because 25% of these buildings are traditionally constructed or maybe indeed listed, we still have to do something to reach these targets. 

However, energy efficiency in traditional buildings is complex. Indeed, sometimes it feels a little bit like a circus balancing act, juggling all the interactions. I have a fantasy of turning this slide into a kind of circus ball juggled by a clown. Sometimes certainly, it feels that that's what we're doing, that we're juggling all the different options and interactions. I've just come from a role where I was delivering MEES compliance work to meet at minimum E across a large portfolio of traditional buildings. And knowing the theory is only one part of the challenge. We need to balance the understanding of what's best for the building and the impact of the occupiers with the demands of our clients and indeed what we can do within our budget. 

I think energy efficiency is currently seen as a least-regret option, but there are substantial risks involved and unintended consequences, and having surveyed buildings which are demonstrating single-measure imbalance, where very good quality work has been done to draft-strip and reduce energy emissions, then over in under ten years, it's demonstrated that without considering ventilation, we can cause more harm than good, and I've stood on site and been demoralised by that very issue. But we know that we can reduce emissions significantly in the historic environment. Last year's heritage count demonstrated that we can do it by 60% by 2050 just through refurbishment and retrofit, and we can improve the operational performance whilst also preserving the historic environment. 

The rhetoric around traditional buildings is that they perform badly. They are leaky and old and cold, and this is constantly what we hear about our traditional building stock. However, let's consider our expectations of these buildings and get some perspective. Many of our traditional buildings are poorly maintained, and over the last some-hundreds of years that they have stood, they reflect some very interesting decision-making. These two photographs I took at the weekend as I wandered around Bristol thinking about introducing this conference. The picture on the left, I think, really struck me as care of our buildings 101. If we want buildings to be more energy efficient, we need to maintain them properly, not complain that they don't perform well when we haven't undertaken the simple maintenance to ensure that they can perform well. 

Climate projections indicate that significant rainfall will increase, and that rainfall will be more intense. So if our buildings already aren't coping with this, they're not going to cope in the future, so we need to consider the changes we make, not only how they will cope now but how they will cope in the future. The photograph on the right, I included partly because I was slightly incredulous and wanted to share this with you, and I just look at it and think, you know, metal vents through rather nice slate uprisers, it's ill thought out, probably ineffective and downright ugly. And almost this picture is the epitome of where we don't want to go. 

Energy efficiency is successful when we understand value and maintain what we have while ensuring change is balanced and well thought through. We have to consider the people, the performance and the potential of our buildings. Without engaging the users, we can consider-- sorry, without engaging the users and considering how they want to use their buildings, really good quality energy efficiency measures cannot achieve the savings that we intend. In terms of performance, we have to consider how the building performs, how the materials, the construction type performs; the state of current repair; and what we are trying the achieve. And we need to specify appropriate solutions bearing in mind the right materials so that adaptation does not become maladaptation. 

And also, as indeed the Shrewsbury Flaxmill project demonstrates, we need to consider the potential of our buildings. We need to look at each building and the area in which they sit and look at what they can achieve. What are they already doing well and why do they do it well, and what needs to be changed so that they can cope now and in the future? We're not trying to turn traditional into modern buildings with modern materials, but rather trying to support their ability to perform at their best. 

Every building can be improved, but the methods we employ can't be one size fits all. I think it's really important that we realise that energy efficiency in traditional buildings is not niche. This is 25% of our building stock. All buildings can be improved, but we need to use the right assessment, the right approach and the right materials. As a really good friend of mine says, get into the detail; that's where the savings are. And I think the really great thing about the list of speakers we have today and in the next session is we're going to get into the detail and really look at how things can be achieved and improved. So, on that note, I'm going to hand over to Nick Heath, who's going to roll us through the policy overview. 

Nick [14:00] OK, hi, all. I'm assuming you can hear me OK. So, I've been asked to talk about the policy context – everyone's favourite subject, I'm sure. I apologise in advance. It's a little bit of a bullet point frenzy, but I'll try and offset that by using pictures only in next week's presentation. 

So, before I set out what I'm going to talk about, I think it's just worth taking a minute to have a look at this chart. When we were discussing this conference a couple of weeks ago, Harry was highlighting the increasing concern around the change in climate, so while I'm droning on, you can take a look at that. I am going to talk through the policy – that's what I've been asked to do – focus on Committee on Climate Change, some government policies, but more importantly, I find up to a point that's sort of words, words, words. I then want to take a look at some of the regulations and standards funding, training and support mechanisms that are in place to help look after our traditional buildings, but also to help make sure they are retrofitted properly and responsible. 

So here we go. It's a bit of a race against time. In fact, I'm just going to set a timer so I know where I am. So, here we are, just before Christmas, Committee on Climate Change launched the sixth carbon budget. Buildings are third list after surface transport and industry, and here's a very quick snapshot of where they think we need to get to, or what we need to do for our buildings to play their part. We have proposals for a minimum C rating on an EPC for all buildings in 10/15 years, and within 7 years for all rentals and house sales, accompanied by a major EPC reform in the awareness that they're pretty dire at the moment. Major increase in all retrofit measures, which for traditional buildings of note includes nearly 3 and a half million solid wall insulation projects. But they do acknowledge the complexity around that, and I'll talk about that in a sec. Oil boilers gone within 7 years, gas boilers gone within 12 years, and they have estimated a cost of less than £10,000 per home, which is ambitious to cover insulation, heat pumps, etc., etc. 

So here are a few slides just to illustrate that, which are nicked from the CCC web page, which is linked in on here. This graph is just showing you the accumulative measures and the uptake of those measures, and it's worth highlighting that for purposes of traditional building, there's obviously concern in some circles about the proposals for, I guess, 30/40% of our stock, our traditional stock, to be insulated within the walls. 

Somethings happened to my presentation, and I'm not sure why. Alice, I don't know if you can hear, but if I could get back to the page-- 

Alice [17:24] Hi, Nick. Yes, which page are we looking for? 

Nick [17:27] It's OK. I can take it from here. Thank you.  

Alice [17:31] That's OK. 

Nick [17:31] So, we were here. Yes, solid wall, 3 and a half million. That's significant, but it's not the dominant measure. Other measure – behaviour or what other efficiency measure, etc., have far more significant uptake, so just to keep it in context, this graph is just showing the uptake in heat pumps, which you'll all have heard about the increase in. For me, the interesting challenge is how we get our traditional stock and other stock up to the required fabric performance in order for heat pumps to be efficient and competitive and viable. 

This is looking at the savings in operating running costs as a result of the different measures. And again, if we look at solid wall, it's not an incidental measure by any means, but you can see proportionally where it sits. Easier wins, other options are there in force. This is looking at job creation. I only include this to highlight what I've circled up in the top right: retrofit coordinator issue. Some of you will have heard of these. Some of you won't. But it is a bit of a buzz phrase and a badge that a lot of people want these days. And as you can see if you look at the graph, there's a significant amount of job creation around there, and I'll talk about that later. 

So, I said that this is a very big document. It's about 450 pages, and they do have caveats within their assumptions, so that's potentially alarming for some people, headlines. They are set in context. They highlight the importance of reforming EPCs. They highlight the uncertainty of cost and benefits of solid wall insulation. Not in a negative manner, but they're acknowledging that further research is needed and further testing, etc. And as I said, this is a very big document, but when they published it, they published a huge amount of background material, so there's days and days and days of reading there for anyone who wants to. 

I just want to look at one of those reports in a little bit more detail, just to highlight, really, that within this report, which is also available at that link, you can find an awful lot of references to traditional properties, heritage properties, so it is something they've thought about and acknowledged, and I've just picked out a few quotes here. They've got a revised list of improvement measures, which are aimed at covering heritage properties. They acknowledge the additional challenges for formally protected buildings as well as traditional buildings more widely, highlighting the technical risk around moisture, particularly intended consequences, but also the importance of these buildings being improved, like Morwenna said at the beginning, and then highlighting the fact at the bottom there is a case-by-case basis, bespoke assessment recommendation, so this is in line with conservation guidance, this is in line with robust retrofit guidance, and so on. 

So there's a lot of stuff about heritage there that's quite positive. I think the challenge from my perspective is how many of the people who write the policies and implement the policies will have read all these background documents. Here are a couple of those policies on that note. So, recent publications. November – we have a ten-point plan from the government. Point 7 covers buildings, and they focus on new build quite heavily. There's focus on heat pumps. We're talking about 600,000 installations a year within seven years. They hang quite a lot on their finance schemes, which I'll talk about later on. They are suggesting they could help get about one and a half million homes to a C rating, which is some way short of where we need to be according to the Committee on Climate Change. It's all slightly woolly, and they also have an increased focus on improving the private rental sector, which I'll come onto in a few minutes. 

The following months, again just before Christmas, we have the energy white paper and some of the headlines in here. There's an ongoing focus on EPC-based targets – energy performance certificates as metrics and benchmarks. There's a lot of concern about these in a lot of areas, but they are here to stay. 

So again, you can see here that they're targeting the C band with a big caveat here where practical, cost-effective and affordable, so there's quite a lot of wriggle room in there. They also referenced their EPC action plan, which they published in September, which again, the link’s at the bottom if anyone wants to have a look. There are an awful lot of actions suggested in there to improve EPCs, but that's the way things are going, and again a restated focus on the private rental sector, together with pending consultations looking at bringing in similar types of minimum standard for owner-occupied homes, support mechanisms incentives, mandates via mortgage lenders and things like that, so you can see the way things are going. 

So, to look at one of these targets in practice, take a look at the private rental sector. We have the minimum energy efficiency standard, which is in force as of a few years ago. Headline figures here. We have a minimum E rating requirement for all rental properties that require an EPC, and I'll touch on that in a sec. Commercial tenancies have a couple more years to get that target. There's a spending cap of 3 and a half thousand pounds per property for a landlord, and there are a number of exemptions. 

So, you are exempt from this standard if wall insulation is deemed to be detrimental, which boils down to the written opinion of a relevant expert, whoever that may be. You are exempt if none of the improvements is possible, if the property remains below an E following all improvements recommended on the EPC or if you spend 3 and a half thousand pounds and you're still not at an E rating. You are exempt if the works would require third-party consent, for example, listed building consent and that wouldn't be granted. You are exempt if the property would be devalued by more than 5%, and for non-domestic buildings, if you don't meet a simple 7-year payback rule, then you're exempt. 

So, proposals. They're further consultation to harden these targets further. For domestic buildings, we have proposals for a C rating for new tenancies in four years' time and for all tenancies in seven years' time, so this is fairly significant, and the spending cap for landlords has increased to £10,000. Worth saying, there are alternative options set out in the consultation, but these are the sort of initial preferred options. For non-domestic buildings, we're looking at a B rating or possibly a C rating – they haven't quite decided – by the end of the decade, again, as long as the upgrade would meet the seven-year payback criteria. And alternative options are also suggested. So again, you can see the way things are headed.  

So what I want to look at now, really-- I mean, there are obviously a lot of questions in amongst that, which we can maybe talk about later, or not, if anyone's interested. I want to look at some of the standards and supporting mechanisms that are in place to promote good work and protect traditional buildings. So, if we look at building regs first. Part L1B, looking at efficiency in existing dwellings. This is peppered with quotes like this. I've just picked out a few which are very explicit in guiding how work should or shouldn't be done. Measures shouldn't involve unacceptable risk of excessive condensation. The exemption-- 

Oh, I didn't talk about the exemption. If I could just go back a few slides. Here we are. So the top bullet there, this E rating for all rental properties that require an EPC, this is a really grey area, and there's a bit of a legal paradox at the moment because there's a perception that listed buildings are exempt. They are not exempt. They are exempt from having to carry out works that would damage the building, but the only way they can find out if the works recommended by an EPC would be detrimental to the building is to get an EPC done. So in a nutshell, you have to have an EPC carried out to find out whether or not you need an EPC. It's all quite confusing, and I think in the consultation they have suggested simplifying that, but it's not simplified yet. Anyway, back to where we were. 

We have unacceptable risk of excessive condensation. Exemption of listed buildings applies only to the extent that compliance would unacceptably alter character of appearance, and again, these terms here, 'unacceptable, people's perception of what's acceptable and unacceptable will differ. As well as listed buildings, you have special considerations applicable for buildings of historic interest, architectural interest and any traditional building, as Morwenna said – 25% of our stock for domestic with permeable fabric and lots of references to moisture. 

So for any of those buildings, the target is to go as far as reasonably [practical?], and again, that's a very woolly phrase, and following that, there's more focus on deterioration of fabric and fittings, guidance followed given by English Heritage and Historic England should be taken into account in determining appropriate standards. And again, more explicit stuff on moisture protection, issues relating to work including enabling fabric to breathe to control moisture and decay problems. And highlighting the importance of the conservation [office?] of use by which token the understanding of the conservation [officer?] becomes particularly important, and I perceive a big challenge there because conservation officers are required to understand everything that's being put forward in applications, which might include quite technical stuff around retrofit and insulation and airtightness and moisture, and it's not something they've had to understand in this level of detail until relatively recently. 

So, that Part L is worth saying is due to go out for consultation to be updated. It hasn't come out yet. No consultation's been issued, but to get an idea of what things might look like, we can look at the Welsh Part L, which has been put out for consultation. So, they are saying things like this. They're proposing further guidance to highlight potential moisture risks associated with retrofit. All improvements should be assessed and designed to manage risk. Where such an assessment or suitability expert advisor recommended, the person carrying out this work should be appropriately trained, for example, a retrofit coordinator – the second time we've seen that – and follow the procedures given in PAS 2035, which I will talk about very shortly. So they also are proposing that whenever you install a new gas combi boiler or extend or convert a building, you'll be required to implement at least one additional energy efficiency measure from a specified list, so that's the way Part L might be going. 

Part F, also directly relevant to retrofit as we've become increasingly aware of the importance of ventilation and indoor air quality. Part F is often criticised in retrofit circles for not being particularly robust, quotes like suggesting that you should try and make sure the building is worse after you've done work than it was before. It is out for consultation. I'm not going to talk through it in any detail. There are a lot of caveats similar to those I ran through in Part L, which are good, in large part, for traditional buildings, but they also include fairly woolly requirements like this bullet here. Aim should be to provide adequate ventilation as far as is reasonable or practically possible, which gives a lot of wriggle room to do the right thing or do the wrong thing. 

So, when Part L for new buildings, for new dwellings, was put out for consultation at the end of September 2019, October rather-- It's just worth saying this is for new build, but it was published alongside a lot of background research reports focussing on issues on issues like ventilation, like indoor air quality, over-heating. And while these are all focussing on new homes, these issues are equally important, if not more so, I would say, for a lot of retrofit projects. 

So, with that in mind, it's also worth noting, if we look to Wales again, they have a consultation document out, closing in a couple of weeks, for a new, approved document, Part S, which will deal with over-heating. At the moment, it's targeting new build only, but I would suggest it will probably end up dealing with existing buildings as well. So the sort of things it's looking at are here. It's only going to apply to houses where you can't cross-ventilate, and it will apply to flats. There are two routes to compliance. You can follow a range of design guide options, which are included in there, if you want to have a look at them. It's stuff like limiting glazing to 50% of floor area, or increasing glazing but putting more external shading in. Or you can go down the route of a detailed over-heating assessment. People will also have to provide over-heating guidance for homeowners. So that is also maybe a sign of things to come. 

I mentioned the PAS 2035. There are a number of publicly available standards. This is the only one I'm going to talk about. This is relatively recent, and it's a requirement for publicly funded retrofit projects to follow this to comply with this guidance. It's a lot more holistic than previous guidance has been. The whole thing merits reading. I've just picked out a few salient points, mainly from the introduction, actually. So this is highlighting the need to reduce greenhouse gas emissions. Very significant improvements need to be made to the efficiency of the UK's building stock. This PAS [port?] worked to those objectives by promoting and defining technically robust and responsible whole building retrofit works. 'Whole building' is a buzz phrase at the moment, which you will see a lot. 

So, it's defining high-quality work that supports improved functionality, usability and durability of buildings; improved comfort, health and well-being of occupants; improved energy efficiency; reducing environmental impacts; and explicitly, which we haven't seen before – the second bullet down – protection and enhancement of the architectural and cultural heritage as represented by the building stock, so it's good to see that in there, and then again, focus on avoiding unintended consequences, minimising the performance gap. So really, it's trying to put energy-related retrofit works into a wider context, acknowledging that energy is super important, but it's not the be-all and end-all. It's part of a puzzle. As it says in that quote, in the context of a holistic approach to retrofit that takes the points listed above into account. So, I'm not going to say any more on that, but I would recommend reading it all if you can. 

On a more technical note and partly as a lead-in into what Paul's going to talk about, I just want to flag up a few British standards, which some of you may have seen, some of you may have not, notably, the S5250. This was out for consultation recently. It's worth highlighting the current version, which is enforced – it's from 2016 – and it's titled Code of Practice for Control of Condensation. The consultation version, which finished in September, has had quite a major overhaul, including changing the title, which sounds like a tiny detail, but it's quite significant, I think. So it's not just looking at condensation anymore. It's a management of moisture in buildings. It's much more holistic, and it acknowledges a greater, or increased, understanding of the importance of getting to grips with all of this. 

Again, you see the whole building approach, a moisture-safe design, and they have a lot of very-- this document has a lot of big annexes, which have some really good technical detailed drawings tables, technical guidance for floors, walls and roofs, and they're emphasising again particular emphasis on managing moisture risks in buildings undergoing energy-saving measures. I'm not going to go through the whole of this, but this is a really good way of approaching things, keeping it simple – something Neil May came up with a few years ago known as the four Cs. So we're looking at a whole-building approach covering context, coherence, capacity and caution, so you can read this when you get the slides, but try and remember that. It's a good robust start-point, I feel. 

It also explicitly highlights our solid masonry wall stock and highlights the care and understanding that are required in their repair maintenance, improvement and extension. It has some very good references to the modelling requirements for moisture analysis when you're looking at retrofit, but equally highlights the importance of a good understanding of things like building performance, vernacular design and monitoring existing buildings. Sorry, that's my alarm. So, it's quite good on all of that stuff. I'm just resetting it. Bear with me. 

There are a number of other British standards, which I'm not going to talk through, but I'll just flag up for you if you're really interested. There are a couple here – 13788 and 15026 – which-- these are effectively standards that go through the Glaser method on the left and WUFI on the right, for those of you that are familiar with that sort of hygrothermal analysis. Quite a lot of BS5250 update is based on this British standards white paper, which was published a few years ago, which is the only freely available of these documents that I'm citing. I would recommend reading that if you can. They're also British standards on conservation of historic buildings, this one written by John Edwards. There's a European standard on improving the energy performance of historic buildings, which is also worth a read. 

The challenge I see with these, which I think there's a lot of very good information in them, but you have to pay for them, nearly all of them. They're probably a couple of hundred pounds each, and they're not mandatory, so there's no requirements to adhere to those, even though they have very good guidance in some cases – so improvements that could be made there. 

Now, I just want to talk through funding a little bit and training and then that's probably it. So a number of finance mechanisms in place at the moment, not that many. The main one people are pinning hopes on at the moment is a Green Homes Grant, which you will be aware of. It's been extended to March next year. It's £5,000 grants or double for low-income households. There's a range of electrical measures, which are split into primary and secondary measures, and you have to carry out one of the primary measures before you can get funding for one of the secondary measures. Primary are things like insulation. Secondary are more things like draft-proofing, double-glazing, secondary glazing maybe. 

Interestingly, it covers quite a lot of things which are potentially good if you look through the eligibility criteria. It covers things like architectural services for drawings and specs. It covers damp investigation works. It covers the sort of moisture analysis that I referred to before, WUFI, and I think Paul will talk through. It covers payback modelling, airtightness testing. It also covers enabling work, which is super important, things like structural improvements, damp repairs, sorting out excessive infiltration, repairing and improving controlled ventilation. I think one of the issues with these is that that could very quickly eat up your £5,000 grant, and I'm not sure how much [indistinct] there's going to be of them, but they are there. 

Also, they're explicit for solid wall insulation, where a survey or assessment identifies condition or installation challenges. These situations must be addressed prior to insulation. It does not cover any measures not included in their own list. It does not cover training costs for contractors. There are also-- I don't have time to talk about it in any detail at all, but there are big question marks over the appropriateness of the insulation systems that will be eligible. Basically, as I understand it, internal wall insulation, room-in-roof insulation and suspended timber floor insulation all require a 25-year insurance-back guarantee, but again, as I understand it, there is no fully appropriate system for any of those, which has that 25-year insurance-back guarantee. You can get product warranties that last that long, but not necessarily the whole package approved, which is required by insurers. What I really mean by that is that there are no sort of moisture-open, fully bonded systems that have that, so that's an issue. I'm not sure how much of this sort of stuff we are going to see installed. 

Anyhow, other funding options we have – ECO. We have Renewable Heat Incentive, which is changing next year to something called the Clean Heat Grant, which I think will be an upfront grant of about £4,000, and then a small number of government funding competitions, so there are a few there. The only things I can say on those, based on having assessed a few of the Social Housing Decarbonisation Fund Applications is there is a wide range of understanding on show, I would say, good and bad in terms of traditional building retrofit. 

While we're on funding, quickly, it's worth flagging up two campaigns – one by the Architects Journal to cut VAT to 5% on refurbishment, repair and maintenance, and one started by Harry to zero rate VAT on deep retrofits – and there are links there, which you should go and take a look at. 

So training, last elements. We've heard about retrofit coordinators. This is the best-known scheme on show at the moment, this level 5 diploma, developed by the retrofit academy. This is what you undertake to get your badge to be a qualified retrofit coordinator. It's quite a lot of online learning. They've just launched a new lower-level award, looking at training 1,000 installers in line with PAS 2030 requirements. CarbonLite Retrofit. This is a long-standing retrofit training course. It's very good. This is being expanded, and people will be able to get their retrofit coordinator badge through that mechanism as well. This is another accredited course, with a level 3 award, delivered by the environment study centre and again focussing on older and historic buildings. 

Other training options. We have ACB if you want full-on training – much more detail in terms of building physics, etc., etc. You have certified Passivhaus designer and tradesperson courses – very good, very rigorous. The ACB also do fairly regular webinars, which are very good and are free to their members. The Green Register is another training organisation for architects, builders, planners and others. They've put together a training package through a futureproof project, which allows [SMEs?] to access the Green Homes grants and become accredited for PES 2030. They run a number of other courses, including these two on retrofit and traditional buildings, which I actually teach. There's a one-day course on principles practice. There's a half-day case study course, and as well as those, there are a number of other relevant courses they run. The UK Centre for Moisture in Buildings runs a two-day course on understanding and managing moisture risks, which is very wide-ranging. And Historic England, obviously, Technical Tuesdays and more. A lot of their Technical Tuesday content is directly relevant to retrofit. 

So, as well as all that training, and that's probably not exhaustive, there is a wealth of guidance. I know a lot of people are unclear on where to look to find more information on all this stuff, but the amount of stuff that's been published in the last 5/10 years is massive. Whether it's case studies, technical guidance, research, monitoring, there's a huge amount of data available. These are only some of the organisations that offer this. Most of it's freely available. 

So what it really boils down to, I think, from the wider policy stuff I started with to the support mechanisms is really understanding what you're doing. This is a quote I use quite a lot, from the Bristol guide on solid wall insulation that we wrote for the council a few years ago. 'It's all about understanding at all levels.' And I put the picture in because I thought it might amuse some of you. My uncle is an archaeologist in Rome, and he saw this high-quality brickwork when he was out on site not too long ago. 

That is it. The only other thing I wanted to mention – I think I still have one and a half minutes left – I was alerted to this consultation yesterday, and I felt I had to include it. Again, it's looking at Wales, who are quite progressive in various areas, but this consultation came out last week with a proposal to develop something called Heritage Partnership Agreements, and it's a potentially interesting route. So it's highlighting that owners that may have listed buildings may often have to take a lot of time and potentially money to submit listed building applications. This can be costly and time-consuming for them as well as the consenting authorities. 

So they're proposing something called a Heritage Partnership Agreement, a voluntary arrangement for the long-term management of heritage assets, and it's something that's negotiated between the owner and the planning authority, and it can include listed building consent for an agreed programme of works to be carried during the lifetime of the agreement, which may last as long as ten or 15 years. This I find interesting, particularly in the context of retrofit, but longer term just management and looking after our historic buildings. This agreement can provide the basis for a comprehensive and consistent approach to the management of listed buildings, and I think-- Do we need to talk through this quote? Possibly not. Oh, maybe just the last sentence. It's just talking about the careful, sustainable management of change reducing the likelihood of unplanned or inappropriate changes. 

So, I know that was a race. That's a summary. The slides will be available. We've got Committee on Climate Change, minimum standards for private landlords, building regs, PAS 2035, British standards, funding, training, guidance, heritage, partnership agreements, and I believe that is half an hour. That's quite enough from me. Thank you. 

Morwenna [46:04] Great. Thanks, Nick. Yeah, that's a whizz through. When I said, 'Get into the detail', that is all the detail, isn't it? And it's really interesting that you mentioned the management agreement sort of pathway for listed buildings that is being looked at in Wales because that is something that in responding to the private rental sector regulations prior to Christmas was discussed by myself and colleagues as a way of achieving energy efficiency, full stop. Would you agree that taking a kind of path like that all buildings might actually be a more successful approach? 

Nick [46:55] Well, yeah. Buildings have to be maintained and maintenance is a fundamental first port of call for any retrofit project. I think the challenge lies in the timescales. As you saw in the policy stuff at the beginning, it's not just a joke. The Committee on Climate Change, there are massive issues on many levels about trying to get buildings up to a C rating or beyond, but that's where they're saying we need to get to, and they're talking about seven years' time. So in principle yes, and ideally in practice, but I think just with an awareness that we don't have luxury of going too softly-softly. But again, that obviously has to be offset by an understanding that if you rush into retrofits and you try and do it all too quickly without understanding what you're doing, then you can make it worse than it was before. 

Morwenna [47:51] Absolutely. I mean, through my own experience with trying to get traditional buildings just to minimum E, the target of C certainly seems like a real tough one, just even in that getting them to E, often the measures are so different to get to C that you're looking at sort of taking things out that we've just installed to achieve a different target in not such a long time, and certainly not in terms of the lifespan of some of the elements that we've just specified. It's a really knotty problem. I guess EPCs, as you mentioned, are being looked at in terms of the BEIS action plan for EPCs. I mean, if you have a silver bullet, what do you think you'd do? Would you tear it up and start again? I liked your point about the fact that's what we've got. EPCs is what we've got. This is what we're going to use. How would you improve it? 

Nick [49:01] It is what we've got. I mean, I complain about EPCs as much as anyone. 

Morwenna [49:05] Yes, me too. 

Nick [49:06] For a serious [indistinct] retrofit, they are-- I mean, they're pretty useless. They're finger-in-the-air indications, but I think there's only so long you can spend complaining about something. I think, like it or not, they're here to stay, so we have to work within that mechanism. But as you'll see, when you look at Paul's presentation and Harry's presentation, for full-on retrofits, they're a world away, and you will see much more robust approaches throughout the rest of today and next week, I would hope. 

Morwenna [49:41] Completely. Some of the-- So one of the points in the chat was about costs of measures, indeed, costs of some of the standards and, sort of, the BSI documentation. Do you perceive-- I suppose it's a double question, washes up at a couple of different questions that were raised in the chat. Do you perceive the cost of these documents to be a barrier? And beyond that, from my perspective, costing of the measures themselves and some of the kind of numbers that are banded around, I think, are think are wildly out. Do you think that we need to do better in terms of costing what we're trying to achieve? 

Nick [50:30] Yeah, definitely. And I mean-- I'm trying to remember all the various strands of your question. I mean, the cost of the British standards, yes, I think is a barrier. I know for big organisations it's not that much money, but for SMEs, one-man bands, they're not going to pay. Most of the people I know won't pay. And you know, I only know a tiny proportion of people working in this area, but they won't pay a couple of hundred pounds a pop for numerous British standards, which they're not even legally obliged to work to. I mean, some of them, maybe the ones that support things like hygrothermal analysis, etc., are slightly different, but the good practice, the more holistic ones like PS5250-- It would be great if it could be freely available. 

In terms of cost of measures and cost of works, again there are big challenges around the Committee on Climate Change targets of sub-£10,000 per home if you're doing a serious retrofit. But there is a point beyond which it financially doesn't make sense, so it's that sweet spot, and again, I'm sure you'll see more of that from Harry and others. There's an interesting-- The background document I referred to in the first section on Committee on Climate Change, I could go back about 400 slides, but I can maybe try and do it while I'm talking. This is the one published by UCL. They include quite an interesting cost table, which was developed by BANES, Bath and North East Somerset, [council?] with what they think is a cost uplift for works on historic buildings and traditional buildings of different ages, and the cost changes are extraordinary, and again they're a world apart from what some people would see as possible relatively cheap measures. 

Morwenna [52:33] Great. So question from the chat from Imogen. Hi, Imogen. She says, 'Is there any research available on the impact of solid wall insulation given the known future of the UK climate projects around temperature rises and the future requirement of associated mechanical cooling and associated CO2 emissions from this?' 

Nick [53:02] So, mechanical cooling. Not an area I am an expert in by any means. There's lots of data around on the impact of solid wall insulation. There's modelling around that looks at future climate scenarios. I don't know if it's something Paul is going to talk about at all, and it's something that Harry might have some resources on as well. I mean, it's the sort of thing I can find links and maybe post them into the chat or send them to individuals afterwards. There is a lot of data. There needs to be more acknowledgement, I think, of the impact of the changing climate because we have to deal with more heavier, abrupt downfalls of rain, which puts more stress on the building fabric, but we also have to deal with increased temperatures and mitigation of over-heating and things like that, so it's a complex picture. It doesn't mean it's not doable, very much so. I think all the caution around retrofitting traditional buildings is very important to understand, but it absolutely shouldn't be taken as a 'Oh we can't do it'. You can do it. It's all about the understanding [indistinct]. 

Morwenna [54:18] Completely agree. And also-- 

Alice [54:22] And I'm going to jump in there. 

Morwenna [54:24] Sorry. 

Alice [54:25] Just give you a heads up, everyone. Just about a minute left of the Q&A, so I'll just let you wrap up, Morwenna. 

Morwenna [54:33] Thank you. Just going to say, Imogen, that my team are currently looking at over-heating and undertaking some research there, so I'm sure that once they're ready, we'll be sharing that. I don't know if we had a minute. There's another quick question about why secondary glazing is only a secondary measure under the Green Home Grant, but I'm not sure whether that's something-- 

Nick [54:59] Well, I'm delighted to say I had nothing to do with writing the Green House Grant, but I would imagine it's because secondary glazing shows relatively minimal benefits in terms of an EPC assessment compared to cavity wall insulation, loft insulation, solid wall insulation, so it's upside down from the perspective of easy wins first. But I understand their logic in terms of trying to force people not just to stick a bit of draft proofing on the windows. The issue is forcing people, as in the private rented sector, to do things in a rush and do major things. You maybe get them to do it the wrong way in some cases. 

Morwenna [55:47] And I think with these targets, we've got a real sense of 'act now, think later', and if that moment of the easy wins are done, we need the bigger hits to start showing change for this... 

Nick [56:04] Yeah, I mean, it's serious. 

Morwenna [56:06] ...to reach the target. 

Nick [56:08] Yeah. 

Morwenna [56:10] The only thing-- I'll wrap up there. Thank you so much, Nick. That is super interesting. I just wanted to add that actually the Part L consultation was published last week along with Part F and closes in April, so really worth getting your ten pence in if you possibly can. Certainly, it's something that I'm going to be working on in the next few weeks. I think, Alice, are we-- 

Alice [56:45] Right, over to you. 

Juliet [56:48] Thanks, Alice. So with our heads full of policy, let's go to Paul, who will hopefully talk us through some of the research that will help us work out how we're supposed to achieve these targets. Paul, over to you. 

Paul [57:05] Hello, good afternoon. I'm going to talk mostly about a case study we did with Historic England, and we developed a methodology to assess the benefits and risks of retrofitting energy efficiency measures. So we looked at before-and-after thermal performance assessments, then long-term monitoring of moisture risk and finally some WUFI modelling with a view to predicting future performance. The house that we looked at is in the New Bolsover model village in Derbyshire, which was built by the Bolsover Colliery Company in the late-Victorian period to accommodate their workforce at the nearby colliery. 

So in 2011, the opportunity arose for Historic England to lease one of the grade 2-listed houses, which was an end-of-terrace house, and it's typical of many English dwellings, both in form and construction. The council agreed to the implementation, the package of measures to improve the thermal performance of the building envelope, and particularly looking at two alternative internal wall insulation systems. 

So basically, the refurbishment was undertaken to measure actual improvements in thermal performance and airtightness, and the principle goals were to facilitate informed decisions on improving the thermal and energy efficiency of traditionally constructed buildings, also increase understanding of the energy use in traditional buildings and looking at the pros and cons of different types of adaptations to reduce energy use, particularly including technical risk due to moisture, and to assess the latter, long-term post-intervention monitoring has been carried out. 

So basically, we've been monitoring the building up until the beginning of 2019, when the council started to carry out further refurbishment works, and unfortunately, due to Covid, we've been unable to restart the monitoring, so we've got a number of years of high-quality data. The main thermal improvements with the internal wall insulation were on the ground floor, where a typical foil-faced foam insulation was used and finished with plaster board. So these represent a sort of more conventional vapour check solution as would be used in new buildings with internal insulation, and I guess that was following some guidance from the early 2000s from the Energy Savings Trust [CE?]. Seventeen internal wall insulation in existing housing, a guide for specifiers and contractors in order to reduce condensation risk. That technical guidance no longer seems to be easily available.  

So we had these two variants. One on the right, with a service zone, but essentially, it's using something like a Kingspan or Celotex plastic foil-faced insulation material. But on the first four we used a more permeable system based on wood fibre insulation, so the original plaster was stripped back on the brick walls and a lime plaster parge coat applied to the brick, and then the hundred mil. of wood fibre insulation was fixed to that, and there was a finishing coat of lime plaster. So it represents an approach which could be perceived as being more sympathetic for solid-walled buildings and using a hygroscopic material such as wood fibre. 

So this essentially, that's the construction details, and these are the floor plans on the left, the ground floor with the PIR insulation and on the right the wood fibre insulation, so it's an end-of-terrace house, so there was the opportunity to insulate the gable wall, which was adjacent to what we would call a ginnel, between the next house. There were some issues, actually, with that wall in particular because of dampness problems because it was built on a slope, so there was water actually running down the ginnel, and there was some evidence of damp in the gable wall, so pretty poor pointing. 

Other thermal improvements were made, including insulating the suspended timber floor and insulating the perimeter of the first-floor void, replacing very poorly laid loft insulation to a depth of 300 mil. with new insulation. Improvements to the loft hatch were made, and a partial insulation of the [party?] walls, and because it was a listed building but at some stage aluminium replacement windows had been installed, these were replaced with timber windows of the original pattern, single-glazed, but then supplemented by high specification secondary glazing, including a sample using a slim profile vacuum glazing, which should potentially give a very good U-value. Also, airtightness measures were affected. 

So the thermal performance assessment using before-and-after testing, first of all we measured in situ U-values of the different walls in a number of locations and including the glazing as well and the ceilings and floors. Then we carried out a [cohesion?] test, which gives you an idea of the whole house heat loss, and we also carried out air pressurisation tests to estimate the airtightness. 

U-values of traditional walls. Usually U-values are calculated from known thermal conductivities of materials. However, with a traditional brick wall, that's not easy because the construction details are uncertain, and the properties of the bricks are largely unknown, so it's necessary to carry out in situ measurements because we don't really want to rely on default values from some U-value calculator. And there's a report by [indistinct] and myself, which was published in 2003 on measuring the thermal performance of traditional brick walls, which goes into more detail about the methods used. 

So essentially, to measure the U-values of solid wall, we need to have temperature sensors fixed to the wall internally and externally and measure the heat flow through the wall in a number of locations using a heat flux meter, as shown on the right. You need a reasonable test duration of a couple of weeks in traditional buildings because of the thermal mass in order to obtain a satisfactory result. Standards usually say you need to measure for 72 hours, but I think that's more applicable to modern lightweight buildings, but for thermal mass, which can store heat, it's really essential that you measure for longer. We had the advantage that the house was empty, but we do do these kind of measurements in occupied buildings. 

So essentially, we can calculate the U-value knowing the temperature difference and the heat flow through the wall and then calculate a U-value using the thermal resistance of the wall and adding standard internal and external surface resistances as you would do normally in a U-value calculation. So some results. We've got before and after measurements here of some of the walls in the building, so typically before-- I'd say the average U-value is about roughly 1.7, but afterwards, depending on the type of insulation, we get U-values varying between 0.2 and 0.35, so we've made some significant improvements by adding the insulation systems. 

And if we look at the glazing, originally in the main bedroom, there was some double glazing, and the measured U-value of that was 2.71, but adding a low E secondary glazing system, we brought that down to 1.63. And similarly, with single glazing in bedroom number 2, the U-value was over 5, which is typical for single glazing, and we again added a low E secondary glazing system and got the U-value down to 1.64. In bedroom 1, which had single glazing, we added the slimline vacuum secondary glazing, and we got the U-value down to 0.81, which is very good. 

Looking at the suspended timber floor, before the U-value was 1.19, and we got down to 0.32 with 100 mil. of wood fibre insulation. The ceiling, originally, there were various thicknesses, and we got U-values of 0.17 to 0.45. But when that was removed and the insulation [read-on?] with a total of 300 mil. of glass fibre, we got down to 0.16, so some quite good improvements there. 

Co-heating tests, essentially, it's a method for determining the whole house heat loss co-efficient through the fabric and from background air infiltration, and it has to be carried out in an unoccupied dwelling. And you use electric heating because it's easily measurable, rather than, for example, using the gas boiler, so we can measure directly the amount of heating energy going into the system. And we also need to measure the internal temperatures in the rooms and the external temperature. Also, it's important to have some measure of the solar radiation because that has an impact on the result. 

So we have a simple layout of heaters, room temperature measurement, thermostatic control and circulation fans to distribute the heat. This is an example of a simple method of analysis that was developed probably about 40 years ago, I would think. So you can essentially plot the data on a graph with the heating power divided by the temperature difference on the y-axis, the solar radiation over the temperature difference on the x-axis, and you can calculate a straight-line relationship and the inset on the y-axis gives you the heat loss co-efficient and the slope of the line gives you the solar gain factor. And it sort of demonstrates, as you can see, that as the solar radiation increases, the heat requirement decreases – fairly obvious – but there is a correlation between the heat loss co-efficient and the solar radiation, so that needs to be borne in mind that you just can't just measure the electrical power. You need, also, to have some estimate of the solar gains in the building. So the co-heating test results, we get nearly a 50% improvement in the heat loss co-efficient. There are other means of analysing the data, and also there's a report out on the thermal performance assessment again, published by Historic England in 2015. 

Air pressurisation, we used the blower door test, and essentially, you need to measure the air flow at a 50-pascal pressure difference. So interpreting the air pressurisation results before, we get an air permeability value at 50 pascals of 13 cubic metres per hour per metre square of floor area. And afterwards, we get down to 10, which at the time met the maximum permissible value at 50 pascals according to the approved document Part L1A in 2010. We also did a SAP assessment, and rather than just rely on standard values for U-values, we actually inputted the measured fabric U-values and airtightness results, and we did the thermal bridge calculations as well. 

And there we are. First of all, looking at the heat loss – this is through each of the elements as part of the assessment – you can see here the reductions in heat loss through the different elements, and here you can see that through the walls, there's an 82% reduction in the heat loss through the walls. And overall, we reduce the whole house heat loss co-efficient by 53%, so we make some very good reductions in the elemental heat loss co-efficients. 

However, we did the before-and-after SAP results, and before, it was already at band E46, and afterwards, we achieved a band D 65, so there was a 40-odd percent improvement. To get any further – bear in mind that no other interventions were made in terms of boilers, improved efficiency boilers, etc. – we would had to have had a condensing boiler to get into band C. I think this demonstrates the point that Nick made about just improving fabric heat loss. It doesn't necessarily give you a really good SAP rating. 

Now, the moisture risk, this was probably one of the most important parts of the research, so we could compare the PIR system with the wood fibre system, and the calculations show, with solid-wall buildings with internal insulation, that the greatest risk of condensation occurs at the interface between the cold face of the insulation and the masonry. So we installed various sensors at this interface, which included humidity temperature and wooden blocks, which are a sort of proxy moisture content sensor. So we had on each floor eight measuring locations. In each location, there was one set of sensors at a low location and another set at a higher location up the wall. 

The blocks are quite a good measure of assessing how the conditions at the interface might affect adjacent timbers, and they can also provide useful readings where the RH reaches 100% due to condensation or, for example, construction moisture from wet plaster. So essentially, you measure the electrical resistance of the wooden block and convert that to a moisture content, so it's a bit like a protimeter. 

The results, so we have results from December 2011 to January-- ah, it should be January 2019. So here we are. We've got the front elevation on the left at the top, and we've got the monitoring position 2 on the ground floor for the PIR system and position 2 on the first floor for the wood fibre. And you can see that this is the humidity, is that they tend to peak during the winter, and particularly for the wood fibre in some years, you get persistently high moisture contents, whereas the PIR is maybe a little bit better. Similarly, on the top right, you get a slightly better result there because the west elevation at the rear of the house is exposed to more sunshine. It's a more open aspect. And the gable wall for both insulation systems – pretty poor results. So there's strong seasonal cycles. However, the sheltered and shaded measurement locations on the gable wall show persistently high humidities throughout the year. 

The first four locations with the wood fibre remain at critical RH values for longer before recovering, then the equivalent ground floor locations with the PIR, which fall to safe levels earlier in the year. We think the more persistent high RH levels with the wood fibre insulation are a consequence of the moisture buffering of the wood fibre insulation, which can absorb quantities of moisture at high humidity levels but take longer to dry out. Briefly, we look at-- These are all the woodblock moisture contents, so really, values over 20% and 30% are shown with amber and red shading there, and you can see that in some locations you get persistently high moisture contents throughout the year. But in 2018, when there was the hot summer, then things are actually starting to dry out. 

So the results so far indicate that the non-hygroscopic PIR system generally produces maybe slightly better performance than the hygroscopic wood fibre system, but a caveat to that is that we really would like to monitor for longer once the secondary refurbishment, which includes improving the pointing to the building as being carried out. And the benefits of moisture buffering may be independent not only on the hygroscopic wood fibre but on the moisture properties of the brickwork, and this is something that we've found out with modelling that, depending on which brick you use from, say, the WUFI database, then you can get widely differing results. I think I need to finish up soon, don't I? 

So briefly, I'll skip through the beginning of the modelling. Two important factors should be considered for looking at moisture risk. How well defined are the hygrothermal properties of a material, and how important they are to moisture performance. So some of the properties need to be known precisely, but other properties may only need to be known approximately. I think with traditional materials, which have a wide range of material properties, that those are probably largely unknown, and the impact on their moisture risk is uncertain. 

I'll just speed through to-- The reason we use WUFI is that it gives dynamic results as opposed to the steady state that you would get from a conventional Glaser method calculation for condensation risk. And it includes built-in moisture. We can look at driving rain, solar radiation, longwave radiation and capillary transport, but attempting to model a house like the new Bolsover building, there's a lack of available data for the original materials of the building and difficult to extract samples. 

We carried out a sensitivity study, and we looked at over 30 bricks in the WUFI database and carried out simulations with the two internal wall insulation systems, and we compared the results with trends in the measured data to try to select a suitable candidate for more detailed simulations. Here we have a year of simulation results for the interface relative humidity for wood fibre with these different brick types. And the line in red, which shows quite a range of seasonal amplitude, is possibly the best fit to the measured response, but you can see here that, for example, that some of the bricks give a very low seasonal amplitude, and they tend to be bricks that have a much higher moisture capacity, and we've found that with the culmination of the wood fibre insulation, its behaviour depended quite a lot on the properties of the brick. So one lesson from this is you really need to have more understanding of the material properties of your walls, for example, because it can actually affect the performance of something like a wood fibre, which you just assume is going to be benign. 

So we compared the models using the sort of best-fit brick with the actual measured values, and we could achieve reasonable fits to the data, but the main conclusions were that we were able to identify a suitable candidate from the database, which we could produce simulations consistent with the monitor data for the two systems. And the exercise seemed to be a reliable means of predicting the behaviour of a construction, provided we could assign an uncertainty to the results. 

In conclusion, one of the key factors in the estimation-- Sorry, the modelling required you to estimate driving rain factors and really with a sort of what's called an adherence factor, and this generally unknown, so what we had to do was to try a range of adherence factors so we could look at the range of possible results. So estimating a reliable rain adherence factor for buildings' materials should be a further topic for research. I think I'll end there before I go way over time. Thank you. 

Morwenna [01:34:34] Great. Thanks, Paul. So we've got, gosh, quite a few questions following that. I'm just trying to gauge – we're a little bit over time – but then that kind of case study was always going to overrun. Super interesting. I just wonder if we could have a show of hands from attendees about whether we reduce the comfort break or skip straight over just before we get into questions so that we can work out the timings. So if everyone could put their hands up if they would like their comfort break or if they would like to skip that bit, and we'll go from questions from Paul straight onto Harry's presentation. Hands up for skipping the comfort break then. Quite a few. Ah, that looks like a winner. Fab. Or maybe it's 50/50. OK. Well, let's get into the questions. I think we'll go straight from questions into Harry's presentation. I think that's a good indication. 

So, I'm just sort of looking through the questions. There was actually a question that came up from Nick's presentation, but I think is quite applicable to this case study, Paul, is that Warren asks whether wood fibre-based insulation is recommended as [indistinct] material for grading the thermal performance of solid walls. However, some suppliers have recommended that the use of vapour-controlled barrier [indistinct] on the warm side. Does this not negate the breathability? 

Paul [01:36:42] I think it does to some degree, and I would've thought that really it should be applied as it was done at New Bolsover where, perhaps, you don't have a vapour barrier but you use a lime parge coat, which can absorb moisture, and there's also a lime plaster coating on the room facing-- as the room-facing finish. But I think one thing [would be?] that the behaviour of the wood fibre depends very much on the properties of the brick, and we've done some other simulations, for example, of the Flaxmill in Shrewsbury, where using wood fibre, as we did at New Bolsover, performs very well. But perhaps in this case at New Bolsover, it's not performing as well as people would've hoped, so I think the lesson is that we need to know more about the properties of bricks in individual buildings, which is actually quite a tall order, I think. But I wouldn't-- 

Morwenna [01:38:28] That would certainly be a big task there. 

Paul [01:38:30] Yeah. So I think it would be interesting to actually do some simulations, adding a vapour control air and see, actually, what results we got for that. 

Morwenna [01:38:51] So we've got another question from Neil Golding, which I think in some ways ties into that and perhaps maybe we've answered. What do you think, Paul, that the real risk of implementing internal wall insulation without having an accurate existing view of the U-value first as opposed to the assumed values? 

Paul [01:39:18] Well, obviously it alters the potential rating of the building, because I discussed this once with a colleague at BRE, and I said, well, surely it doesn't really matter all that much because the brick is such a poor insulator anyway. Why don't you add the insulation? Then it really shows a significant improvement whatever the performance of the brick was in terms of the original U-value of the wall. But it does make a difference in terms of, perhaps, your SAP rating, because the SAP rating, if it was, like, an RD SAP, it would just assume that the thermal conductivity of the brick was 2, whereas actually we found that, generally speaking, that the thermal conductivity's a lot lower. So the U-values of brick walls are better than you think they are, but not by much. 

Morwenna [01:40:45] I think that's great. I am conscious of time, and we do have an awful lot of questions on this case study. I think that what we can do is we'll take a note of all the questions that are coming in, and we'll maybe pick this up in the discussion in the next session so we have the opportunity to really dig into some of the points that are being made in the chat. But thank you so much for that, Paul. I think what we'll do, having cancelled our comfort break, is move straight onto Harry, so yep, go from that research straight into actual projects and looking at what Harry's been up to. Thanks. 

Harry [01:41:33] Thank you very much, Morwenna. It's a great honour to be talking at a Historic England conference, so thank you very much for inviting me. So today, I'm going to be talking about one project, but before I do, I just wanted to give you a feel for the range of projects I've worked on as an architect, deeply involved in the retrofit of existing buildings for the past decade. And I thought I'd just start with a slide that gives you a feel for the range of building typologies and their ages that I've worked on. 

And as you can see on the left, say, where it says '1840', that's a grade 2-listed semi-detached house that we've done a whole house retrofit on and we've been monitoring since 2013. The project we're going to talk about today is the 1901 mid-terraced house in Bourneville. The 1920s, my mum's semi-detached house in Hampshire. 1978 is where I'm talking from now. This is my own house, and I'm currently on site retrofitting a Walter Segal self-build house from 1988. That's just round the corner from me in Lewisham. And kind of incredibly, we're also retrofitting a house that's only eight years old, which is an infill in a terrace in Kentish Town in Campden. 

So just before I get into the detail of the case study, I just wanted to give a quick picture of the kinds of projects that we've done a detailed retrofit on. This project is in Clapham. It has a weather station, a Historic England weather station, on the roof, and there's been a project to look at the lofts and ventilation and moisture gain in lofts. But I've also got 20 sensors inside the house, and we've got an incredible picture of moisture within the house, and I saw a lot of the questions coming up and sort of keen to get involved in that kind of discussion. But today, I'm not really talking about moisture, although it is a sort of fascinating and very important, complex topic. 

So just going to race through these. So this is a mid-terraced house in west London, and here we met the Passivhaus target [the benefit?]. And here you'll note that we met the airtightness of one air change per hour, and that really was challenging. And that needs a lot of very, very invasive work and incredibly good construction and workmanship on site. 

So then my mum's house. We actually decided that we were going to just soften down the airtightness approach and not tape the [joist stems?], still tape all the junctions between windows and walls and junctions between walls and ceilings but not go that deep. We lost maybe two air changes per hour, so we still got a very good, low airtightness, low infiltration, of round about three air changes per hour, and again this was targeting to meet the AECB Silver Standard. 

Each of these projects has got a very different set of details. So this one, for example, has got cavity wall insulation and some internal wall insulation. And then finally where I'm talking now, which is the little window on the right-hand side of that central image, and this is my own house, and I'm carry out a step-by-step retrofit to this house on Sunday. It has taken about two and a half years so far, and I'm really learning as I go, and we're doing all sorts of experiments, in particular, about overheating, so I've got quite a lot to share on the overheating debate. 

So today's case studies. So this is a mid-terraced house in Bourneville. This is actually on the boundary of a conservation area, so to the bottom of this image is within a conservation area, but we're just outside it. And it's a rather kind of typical Victorian street. Here you can see the Cadbury factory in the background. The house is somewhere in here. Interesting to note on this just how many trees there were. There's no way near that many trees now. So here's the house, and you know, in the past when I was asked to look at doing a whole house retrofit, I was really very focused on targets and insulation and U-values, and I have to say that I'm not far more focused on low carbon, moisture robustness and longevity, and it's been a sort of path that I've been taking. And here we've got some rather lovely historical detail. 

We've also got a very attractive rear brick elevation, and typically for a whole house mid-terraced retrofit, you might look at internal wall insulation at the front and then external wall insulation at the rear. But I actually felt in this case, it would be really quite detrimental to the character at the back of these houses. And so through a process of discussion with our clients, we decided not to put external wall insulation at the back. 

So internally, there's some lovely, lovely features here in the hallway and these lovely quarry tiles on the floor of the hallway. And the house is fairly typical. You have a front living room entrance corridor through to the rear addition, dining room at the back, and here it's got a little extra extension at the back. This is the client. She is a conservator at Historic England, and this is George, who works for Energy Systems Catapult, so they're both very knowledgeable and very committed clients and they're really keen on reuse of materials, which is wonderful. And they even lifted this rather nasty laminate floor that was down in their house before to reveal this, and they actually managed to sell it or give it away through a freecycle scheme locally. 

So in looking at how we were going to structure the project, we wanted to think very carefully about, what decision-making processes were we going to go through and what would inform those? And our clients were very keen to make this a case study of what they called achievable and pragmatic retrofit, and we certainly have followed the whole house retrofit approach put forward by the STBA. But we also wanted to bring other elements to the project, so perhaps the key relationship was with Jane Anderson, who is a life cycle analysis expert, and she gave a lot of input into helping us make low-carbon decisions, and I'm going to share some of those through processes with you. 

So this drawing is maybe one of the most important drawings in the project, and I don't expect you to read all the labels, but what is important is that the blue labels, the blue notes, are moisture-related comments about the existing building. So before we get into U-values and targets and lovely extensions, we're trying to forensically understand the building, and we're trying to identify risks. And in the past, I might have focused a bit more on how thick the insulation was and whether we can afford PV panels, and now I'm really sort of letting clients know right from the beginning that actually getting the building fabric up to the very high standard is the most important first step. 

So a term that I quite like is 'retrofit ready'. So retrofit ready means that your building is essentially shedding rainwater well, is not pulling moisture up from the ground and is managing internal levels of moisture well, as well. Now, of course, most buildings at any one point in time have a number of those issues going on, and as you can see here – these blue comments – there were quite a few issues. I'm not going to go into detail into them but just want to highlight them. So then a next early drawing would be, if we were going to try and achieve a thermal envelope that is continuous, how might we do that and what happens at junctions? And of course, junctions are really critical. They're the bits where things can be a success or a failure, so we highlight these, really, from a very early stage.  

So you've modelled the building in the Passivhaus planning package, and we actually used the design PH plug-in to sketch up. So we've built the geometry of the house, geolocated it, applied the thermal properties to the walls, applied shading elements and then obtained an existing space heat demand and then, with some proposed measures, a proposed space heat demand. 

So through those-- Through that analysis, we realised that we could probably reduce the space heat demand of the building by about 70%. We've actually softened a bit on this, so it might be a little bit lower than this, but it's of that kind of order. And I mentioned earlier on about the decision-making processes. I don't expect you to read this again, so don't worry. I go into a little bit of detail on the following slides. I just want to share th-- This is the little tool that we developed and that the client really bought into as well, which is just a simple Excel spreadsheet, and it identifies-- Actually, I'll go back in. It identifies the actions that are needed on the left. Now, these might be 'do we move the door on the second floor that's in the middle in a slightly unusual location or not?' And we suggest a minimal intervention, and then we assess it in terms of its historic assessment, its carbon assessment and its thermal assessment. 

So we're using these three kind of lenses by which to make decisions, so we'd say OK, because very much as Morwenna was saying about issues – she had the image of the clown trying do this balancing act – well, we're doing this all the time. How do we balance these things? Because of the imperative to reduce carbon and to reduce energy emissions and also to retain the wonderful character of our built environment, how do we balance it? So we just developed this simple tool to say, 'OK, well, let's just look at each one individually and let's try and make a holistic decision'. So we found that very useful, and again there's not really time to go into a lot of detail on this, but it was a very nice way of recording and tracking change through the project. 

So this a little sequence of slides to just give you a sense of what we did to the house. So this is mid-terrace. We've lost the terrace either side. You'll notice that at the back, there's little extensions. We've got a very small garden room extension that's very modest in size, and we've put new insulation into the house. We've put a whole house demand control, kind of put an extra ventilation system in. We are installing triple-glazed sash windows, in this case, from the green building store, at the front of the property and a few at the back. But we're going to take out the glass from all the existing aluminium frame windows, and we're going to re-use that in the little glazed garden room at the back. So we're very excited about this re-use into the rear extension. 

We're going to re-use bifold doors, various [indistinct], floor tiles, timber. But really rather wonderfully, we measured how many kilograms of embodied carbon there is in a toilet, and naturally, the clients decided to keep their toilet. And you know, so often toilets are just thrown out because they just look a little bit old, or if they don't fit the kind of design vision. This house is very much trying to say, look, let's value everything that's there. Let's value the historic building fabric, but let's also value the carbon content and just things that have been made that actually function perfectly well. 

So we're going to use locally sourced timber for the rear extension. We went on a very detailed analysis of how to do the foundations, and I'll go into that in a little bit more detail later on. We're going to recycle the window frames. I won't keep going, but we've got this long story of things that are going to be recycled or freecycled, and again, our clients, George and Sarah, have been wonderful at following this through. 

OK, so this moves into the sort of second part, which is, this is really the context of when this building was built and how it was heated, and this is where all those enormous carbon emissions were made. And I just got thinking about what might the full carbon history of this building have been. So I produced this little sketch back in June 2019 just to say, well, how can we kind of put all these layers of building change, services change and sort of new gas boilers coming in, so it was actually quite fun researching when did gas lighting come in and when did gas cooking start and when did the first gas boilers come in? So we sort of put together a rough idea of what happened before, where we have that dashed line, and then try to sort of think about to what extent that might inform how we move forward. 

So after doing that, we then also wanted to think really deeply about the relationship between embodied and operational carbon, so it's very easy to say, 'Right let's go all out. Let's insulate everything. Let's replace all the windows. Let's just upgrade the lot.' So you do end up with a lower operational carbon, which is that horizontal line at the top, or near horizontal line at the top, but you obviously have this far larger-- well, it's often called a carbon burp of embodied energy. 

So we just wondered, well, what happened if you tried to get a lower embodied energy? And you would have a higher operational, but maybe there's a kind of interesting point at which those two lines cross, and given that we have an imperative to significantly reduce carbon emissions, not by 2050 but by, really, 2030 should be the target. In fact, that's the target in most councils that signed up to becoming zero carbon by-- then really, they kind of-- the hat that I'm wearing is really how can we really keep operational energy down [indistinct] optimum retrofit embodied carbon. 

And I don't really have the perfect answer. As Morwenna said, there's no 'one size fits all'. It's about a very bespoke approach. It's about listening to the building. It's about the relationship with the clients. And this listening, for example, in this building is very much a client-driven approach, and it's because they believe they can use it, so I'll talk a bit more about that in a minute. 

So I won't go into detail here, but this is a summary of the life cycle analysis approach we took with Jane Anderson. Just very briefly to say that module A is about the carbon emissions involved with the extraction and construction of this certain element, so module C is the end of life. So what happens at the end of a life of that building element? 

So we built a model of the building, and then we measured all the insulation and the glass and the timber, really the whole house. And we put it into a giant spreadsheet, and we said, 'Right, let's work out the embodied carbon of this house'. And what we did was-- So we worked out the embodied carbon on the house. Then we decided to say, OK, well, this is our proposal. So we have the little garden room there on the left, and we have a series of small interventions that we've made, and what could we compare that to. So we actually decided to look at a typical-- Sorry, I'm just going back to the report here because [indistinct] label [appearing?] of my forwards and backwards icons. 

So we compare that to what would a typical house extension be like? I'm going to come back to that in a minute, where we compare the carbon emissions of the two. So just briefly here, in looking at what the foundations were for this garden room extension, we said, OK, well what if it was a concrete raft? What if they were Heli-Coil steel piles, and slightly crazily, but quite fun to explore this, what if they were timber screw piles or even timber round piles? And eventually, by working through all these and looking at the detail and the buildability, we realised that actually, working with our engineer, that very small cement-free or very low-carbon pads of concrete with a little brick on and little timber joist would actually be the lowest carbon solution apart from the timber screw piles that they had to be four metres long, and there was a whole buildability question, and actually they probably had to be rammed in and might have just disturbed the building. 

So in looking at the servicing of the building, we've got on the left the gas boiler, and on the right, we've got some ceiling-mounted radiant panels. And the gas boiler, we think it's on its fourth iteration, and the radiant panels on the ceiling-- We've got home-schooling going on here, so apologies if you can hear a little bit of yelling in the background. It's obviously a very fun lesson. So we then [indistinct] to say, 'Well, why don't we compare the whole life carbon of an open coal fire, which is what the house had originally, to a gas combi boiler, to radiant panels and to an air source heat pump?' 

And at the moment, there's obviously a very strong drive to air source heat pumps, and we at least wanted to answer the question, what is the whole life carbon of the radiant panels? And the issue here is that the radiant panels are using direct electric heating – direct electricity – and they will cost about four times the amount of gas, but the air source heat pump has a co-efficient performance of about 3. You'll actually end up-- Your bills would be significantly lower with the outsource heat pump. But then you have to factor in the fact that the air source heat pump needs servicing each year. Radiant panels might have a 30-year no maintenance lifespan, so we're trying to balance all these different factors and at least ask the question. So we even went to the extent of asking the question about, well, what if there was a steel lintel for an opening compared to a timber lintel? And we could really see that there were significant advantages in using a timber lintel where possible. 

So going back to this little table that I drew, I was really interested to see, well, what would it actually look like if we seriously actually quantified it. So we actually said OK, well, those original bricks, that big carbon mission there, the original construction, that probably would've been a coal-fired brick oven somewhere. And then looking at all the different renovations that might've happened to the building at the time, we produced a table where we sort of did every ten years through the history of the building, and we looked at all the different elements that had been done and worked out. When was there an extension, and what were the carbon emissions of that? 

And we sort of assumed a certain amount of internal finishes every ten years and tried to kind of put together an overall carbon profile of the building. And it looked something like that, and I guess what's kind of quite striking is that black-green there, which is that we've actually discovered that in our initial embodied carbon, because the amount of wood fibre that's being used might well be negative for this project. So it's really heartening to better compare the sort of previous history to the current. And of course, where the fundamental part of this is – these are the crosses – is the decarbonisation of the grid. So you can see that the carbon emissions of electricity are significantly reduced and going to keep going down. 

So going back to this graph, we also thought, well, let's talk about this lower embodied versus higher embodied, and let's see if we can look at what the extension might have been for a higher embodied compared to lower embodied, and the regular extension has got larger openings. And we considered all these with the client. We just kept saying, 'Look. You could have a two-metre opening here, but it would do this, this and this, and it might not just be going from a timber to a steel lintel, but it might be going from a timber to a steel to a bit more of a padstone to possibly a bit more of an underpin'. So there's a kind of knock-on effect with all these decisions, and really the sort of imperative was, right, let's just and balance the carbon and the historic building fabric and then the thermal performance. 

So we sort of designed a kind of regular extension to compare to, and then we measured the embodied carbon of that. And so we've got the low-carbon retrofit here, where it says '-2.5 tonnes', where we looked at all the different building elements that were going to be used, and then we looked at the standard retrofit, which is probably more like 12 tonnes in terms of the intervention. And when I say retrofit, I think it's important to recognise that it's not that often that people carry out just a retrofit on their homes. There are kind of trigger points for retrofit that are very often a little extension or a new kitchen or a loft extension or having to reroof, and I think it's very important to think about buildings in that way. They're not just a static thing that get retrofitted. They're things that get adapted over time. 

So again, we tried to quantify this, so we looked at the current operational, and then we looked at the standard retrofit with the operational energy arising from that, and then we looked at our low-carbon retrofit and then the operational energy coming off that. And so through this quite fine-grain analysis and iteration and driving our structure engineer crazy and our wonderful clients really making a big effort to run through decisions, and they're still going on, have actually resulted in this avoided impact.  

So these are just a few pictures that are kind of live. I said this was a live retrofit, so it was actually live. I had site meeting this morning with our clients. So it's in Bourneville in Birmingham, south of Birmingham, and we've been doing all the site meetings by Zoom. I'm hopefully going to go to site soon because it's pretty challenging, but you do, after a while, start to get a hang of it. So I get sent a bunch of site photographs just before the meeting. Sometimes we do a live video, but I get pictures and send sketches, and it's a pretty good way of working.  

And this is to highlight really the sort of extraordinary nature of retrofit, where you look at a floor that had the floorboards on, and it looks alright, and then you take it off and you see this. And you realise that actually that this whole floor's been lifted maybe twice before, because you can tell from the plastic membrane that's been put down. And this doesn't have blocking between the joist, and there's just a litany of issues going on. You'll also notice water, which is another drama that I won't go into now, but just wanted to share that. 

And this is our client lovingly insulating and making the floor, being very careful about managing moisture and drying out the floor before installing anything. I think you just can't emphasise this enough. It's really imperative to let walls dry out, let fabric dry out, before you insulate. Otherwise, you really are locking the moisture in. And just to refer back to Paul's talk and the sort of long-term trajectories of moisture, we on our Rectory Grove, Clapham project that we've worked on and we're still very close with the clients and still monitoring it and still accessing the data, we noticed it was about six years before the moisture level started to equilibrate, so we noticed year-on-year drying-out of brick work. So it'd get wet every winter and it would dry out in the summer, but the overall trajectory of the up-and-down cycle was just dropping, dropping, dropping, and it really was about six or seven years. 

So just to say that even on site, local carbon decisions are still being made. We were going to be opening up that window on the right a bit further to have a bifold door, and actually as a cost-saving measure, we're now just going to have a single door there, and it's really worth saying that low carbon is very often low cost and is very low impact on historic building fabric. And so those three work terribly well, and in this case, it's less glazing, which obviously has a much worse U-value than wall. 

And this is just a little sort of-- On Zoom, this is how we work now, so we annotate drawings live on Zoom. And this just shows the bifold door being changed into just the single door with my favourite colour of pink pen, live in the client meeting. 

So then just one other thing is insulating hearths. This might be a detail that people are interested in. We didn't know what the condition of a hearth was going to be, and it just turned out to be kind of super loose rubble, like almost no substance [indistinct]. So we developed a detail and basically using geocell and limecrete, so really keeping this as a breathable floor element, so we've got quarry tiles on some bedding mortar. 

So that's the end of the talk, and just to say if anybody's confused, because I used to work for a company called Arboreal Architecture, and as of today, I'm now 100% on RAFT, so we're really focusing on the retrofit of existing buildings, and very excited because we're working on five school buildings at the moment with Lewisham council, as shown in that image. And we're making proposals to these schools, so we're really turning them into healthy zero-carbon environments. So if anybody's listening and is connected to a school, then please do get in touch. So that's the end of my talk. Thank you very much. 

Morwenna [02:10:22] Great. Thanks, Harry. I have to say I love this case study. I'm on my, what, fourth renovation of my own homes and it's exactly how I might go about it, and I do go about it and am currently constructing my utility room solely out of materials scrumped from local skips. 

Harry [02:10:43] Wonderful. 

Morwenna [02:10:44] So I really do love the re-use and that kind of fine detail of decision-making, because once you realise that every action involves embodied carbon, you realise that less you act, the less carbon is expended. But I suppose from a personal perspective, where I might do this for my own house, but when I go out and I try and retrofit, sort of, estates with timescales and budgets to hit, I wonder what you think is sort of the key scalable elements from your learning from this project. 

Harry [02:11:27] It's fascinating question. I mean, I have to say that I've had a baptism of fire, because with RAFT, we're moving to a larger scale of project, and I'm used to smaller projects with reasonable budgets, and just to answer a question from previously, £500 per square metre for a whole house retrofit is my take on costs, which is nowhere near the £10,000 or even £20,000 that people talk about. So we used to much more generous budgets, and we've actually just taken part in, to go back to the previous slide, we've just taken part in a public sector decarbonisation funded for these five schools. 

So this is – I don't know if anybody knows about this – but there's a £1 million pot of money that the government opened up, and there's a funding criteria of £500 per lifetime tonne of carbon saved for the retrofit measures. So I've had to go from the sort of being able to do WUFI analysis and custom cup testing and, kind of, fine-grain analysis in loving details to having to make something work at big scale with really quite a limited budget. And really, a point that Paul made earlier on was that if you just put a bit of insulation on, you've already radically changed things. So we sort of took the view that cavity wall insulation, although we'd like to meet something like [indistinct] target, that cavity wall insulation in three of the cases was actually a significant win, and now it's fairly cheap. And obviously, there are a lot of issues with cavity wall insulation, and you have to make the moisture robust, and there's, you know, very aware of the new industry of taking cavity wall insulation out. And obviously, we don't want our projects to be part of that. 

The kind of key measures that we identified were provide good ventilation, get some insulation in and put in an air source heat pump. And those measures were not the whole thing that we'd love to do, but they were a significant decarbonising sort of element for each of those projects that we could actually make work with, kind of, government-style funding. So the thing is that windows are a massive issue as well, but the criterion that the government has for meeting the funding for those just doesn't stack up, so we couldn't make them work going for-- because very often, you're working with existing pre-performing double glazing rather than single glazing. I'm not sure if I've fully answered your question there, but I think I've skirted around it a bit. 

Morwenna [02:14:12] Yeah, I think you have, and I think I'm really interested in that detail decision-making spreadsheet that you've put together, exactly that balancing all the heritage issues. One thing that we haven't really mentioned is significance, when we look at some of this work to list buildings, or indeed, I mean, I think if you can get it right for a listed building, then you should apply it to all traditional buildings. But the significance side of things is something that we need to balance carefully, and to have that-- Yeah, and I'd talk to you more about your exciting spreadsheet because certainly, sort of, coming into my role, looking at that decision-making, how do we practically apply our decision-making? And I think one of the questions, or comments, from Warren in the chat is that, you know, really interesting presentation and case study, but as an architect, I struggle to balance embodied carbon with energy efficiency in making decisions due to lack clear rules of thumb. Is there any guidance that you'd recommend? 

Harry [02:15:23] Yeah, that's interesting. So I think any rule of thumb has to be caveated with 'it depends on the context'. 

Morwenna [02:15:33] So true. 

Harry [02:15:33] I think going back to Paul's presentation, where we saw some, I would say, fairly alarming levels of moisture in the walls, the orientation of a wall and the degree of rain and shading and the quality of the mortar and the quality of the brickwork, these are all such a wide range of variables that we have still have to be so careful about making rules of thumb. One rule of thumb that I could say would be that somewhere between 40 and 80 millimetres of wood fibre is in most cases going to be a fairly good, safe bet, and remember, I said 'depends', because if you do that and you haven't repointed, then I think you could be asking for trouble, because it all depends on the condition of that repointing. 

I noticed early on that Paul talked a lot about bricks. My experience is that I've found that the mortar is even more of a factor than bricks, and it's possible that Paul, when he refers to bricks, he means whole assembly. But I do think that if you're internally insulating solid brick walls, you've just got to look at, you know-- People want to insulate a wall, and I say, well, if you want to insulate a wall, you need to make sure that your pointing is in great condition and it needs love and care, and it also, even more importantly, needs ongoing maintenance – even more critical to repoint your wall in the next 20/30 years when you've insulated, because you've got a raised level of bricks. 

So I think that that's a sort of rough feel for walls. I think mechanical extract ventilation and a MVHR, the sort of debate between the two is quite a sort of rich seam. MVHR can be quite invasive in a building, and it can go wrong; it can be installed wrong. MEV, I think, is a bit less invasive, and there's a bit less to go wrong, so it's probably more robust long-term. 

Other guidance? I think loft insulation, generally, or roof insulation. Just make sure that you're ventilating above your insulation and particularly if you're insulating between rafters, but I'm not too worried about really good U-values, sort of 0.15 to 0.2, for roof spaces, as long as you're making sure that that's getting lots of air underneath the tiles. Yep, there's a couple. 

Morwenna [02:18:20] I mean, I would say that it's definitely something that Historic England are looking at. From my own practice as a building surveyor, I've struggled with that balance of embodied carbon and energy efficiency decisions myself. And coming into this role is that knowledge of-- I mean, as you say, Harry, it is a case of 'everything's different', and its 'difficult rule of thumb' is always caveated with 'it depends'. 

But I think with the pressure of those targets you mentioned, the fact that many local authorities have signed up to a 2030 target rather than a 2050 target, it's that element of acting wisely if not always acting with every piece of information that you could possibly have, and how we go forwards in a kind of intelligent but swift manner. I think that's going to be key. I think there's a couple of points about costing. I think Julian says getting prices for £15,000 to lime repoint and £15,000 for a heat pump. I mean, from my perspective, those costings do vary hugely, depending on what part of the country you're in and, indeed, the skills of the contractors that you're using and the time that you want to take. Is that your perspective and experience as well, Harry? 

Harry [02:19:53] It is, it is, most definitely. I always think of a better answer after I've answer a question, so just to go back to Warren's question about the rules of thumb-- 

Morwenna [02:20:02] Well, that's why we've got the discussion next week. 

Harry [02:20:05] So my thought there, really, is something I did say in my talk, which is just keep it simple and do a bit less, and it's so tempting to an architect to always be doing more, but sometimes you can actually just make your interventions a little bit less dramatic or a little bit more bespoke and a bit smaller and a bit cuter and a bit more re-used and I think you're on the right track for doing a low-carbon retrofit. 

So anyway, yes, I mean, it's interesting, isn't it, because somebody's said that £500-- I think just by email, actually. Somebody just sent an email to me saying, '£500 per square metre is a terrifying figure', and other people saying, 'Are you sure?' So yeah, there is such a wide range in costs. It's extraordinary. I've been getting some variations from this project in Bourneville, and I've had to sort of double-take at some figures because I'm used to London prices, and the prices are quite a bit lower in Birmingham. So yeah, there is immense variation across the country. But there is sort of 15-- 

Morwenna [02:21:14] And of course, you have this variation in material costs as well, in terms of sustainable materials, and also that conservation uplift if you're working on a listed building was mentioned previously, wasn't it? 

Harry [02:21:29] It's a good point. And just to add to that, actually a lot of the eco products, if you don't-- So our client, George and Sarah, they've been brilliant because earlier on I said, 'Look, just be aware that delivery costs can become quite a large part of your overall material costs'. So we tried to just pick on supplier and as few orders as possible, so it's all been quite carefully planned rather than picking and choosing. So most of these products are not down the builders' merchants, are they? So they have to be specially delivered, so I think that's an area where you can work in a bit more efficiency. 

Morwenna [02:22:11] It has to be s-- It is where some of my optimism lies in all of this, is the continued development of our sustainable materials, when you look at the move for bamboo to take over from steel. And indeed, actually the re-use of steel framing, it's elements like that, I think that we can as a market drive more development, more demand and just push for that lower embodied carbon, or indeed, those materials that sequester carbon in their production. And that's where we need to be headed. 

Thanks, Harry. That's brilliant, and I look forward to, I'm sure, picking up many of these points next week in our kind of round-table discussion. I just wanted to say that James Smith has made a point in the chat: 'We need to retrofit 26 million houses in 20 years. That's over one million houses a year. This equates to about 20,000 a year in Shropshire or 55 every single day. How do we do this with the necessary deep retrofit level?' I think, as I mentioned in my opening, the scale of this challenge is enormous, and I think when you work doing those retrofits in this industry, sometimes one can become overwhelmed by the idea of how much there is to do, how few skills, how many challenges, but also how wrong it can go. But I think, as we've demonstrated today, there's lots of good things, there's lots of good information and certainly a lot of people trying to make the good decisions and then share them through formats like this. But yeah, it is overwhelming. 

I'd like to thank our speakers today and the team behind Juliet and Alice for throwing me questions in a format that I can read them. And, yeah, thank you very much, and I look forward to next week.