S2E33 - Jae Cotterell, Director of Passivhaus Homes

Passivhaus Homes helps build net zero carbon houses. They provide technical support to those building economically sustainable houses to a Passivhaus standard in an effort to combat climate change.

Jae Cotterell is an author and architect, with experience in designing certified Passivhaus buildings, Jae is motivated by working to produce quality, aesthetically pleasing buildings achieved through thoughtful design and teamwork with people who share common values and interests. Whilst being pragmatic about material choice she prefers natural, locally sourced products.

Appropriate use of energy is critical in today’s world and Jae believes the best way she can contribute as a Passivhaus architect is to ensure that the building’s fabric is insulated and detailed well and to ensure the whole team has a proper understanding of building physics. Jae is the author of the Passivhaus Handbook.


  • Achieving net zero carbon within a 10 year target
  • Working towards a better future as a whole industry as opposed to individual efforts
  • An introduction to the Passivhaus German standard
  • Building energy efficient houses to match zero carbon energy grids
  • What is embodied carbon and why is it so important?
  • The RIBA 2030 Climate Challenge as a target for operational carbon and embodied carbon.
  • The difference between retrofits and new builds and the challenges of working from existing buildings
  • The personal benefits of meeting the Passivhaus standards
  • The pros and cons of natural insulation
  • ‘Resistance to change’ from large volume house builders
  • Enforcing a ‘step-by-step’ system to uplift an existing building in 5-10 years
  • Reaching net zero carbon should be a government effort, not an individual responsibility
  • Is preserving old buildings the best way to move forward?
  • Declarations of a climate crisis are only worthwhile when followed with practical change
  • How working with Passivhaus Homes has positively affected Jae’s quality of life

Useful links:

Jae Cotterell’s Linkedin

Passivhouse Home

Passivhaus Handbook

Listen to more podcasts here.


Intro  0:08  

Welcome back to the Green Element Podcast where we feature business leaders and innovators transforming their operations to be more environmentally and socially sustainable. I’m your host, Will Richardson and I can’t wait to meet our guest today and help you on your journey of sustainability. 


Will  0:08  

Welcome back to the green element podcast where we feature business leaders and innovators transforming their operations to be more environmentally and socially sustainable. I’m your host, Will Richardson. And I can’t wait to meet our guests today and help you on your journey of sustainability. Today, we’ve got Jae Cotterell on the podcast, and she is a massively inspiring lady who has been working in the industry of greening up homes and houses for over 10 years now. And it’s really cool talking to her and having talked to her because of that understanding of what we need to do and how we need to do it and that knowledge that she has and to be honest with you that conversation  could have gone on for a lot longer, and just exploring more and more ways that we can reduce our environmental impact when building homes. Yeah, hope you enjoy the episode as much as I did. Hi, Jae, thank you so much for coming along to the Green Element podcast. You’re Jae Cotterell from Passivhaus Homes. Please tell us more about Passivhaus Homes.


Jae  1:26  

Yes, it’s great. Thank you for inviting me Yes that’s great, thank you for inviting me on the podcast. Basically, Passivhaus Homes is a business that is helping people to build what’s called net zero carbon houses. And the idea is that we provide a route or a pathway for new houses so that people can get there simply, economically, and we provide the support. So whether it’s a self builder, whether it’s an architect, whether client group like a council, the idea is that we provide all the technical backup and a pathway through to ensuring that at the end of it, you get a netzero carbon house at the end. And part of what we do is also education, we’re very interested in passing on knowledge. So that, you know, I said to you when we when we initially had a chat, that, we’ve got 10 years to go from where we are, which is very poor housing and an industry that builds very poor quality housing. And then we’ve got 10 years 2030 to get to net zero carbon, which is an incredibly short timeframe. And so it’s not about people doing exciting things. It’s about the whole industry transitioning to doing something much, much better than what they’re doing now.


Will  1:47  

And do you think it is a case of everyone having to work together for that?


Jae  2:39  

Well, if you’re going to, you know, there’s no, everyone. That’s what that’s what climate change studies and science all tell us. We’ve all got to be doing adequate reductions in carbon. So that means it’s not just about you know, the old eco architect, or the odd passionate individual designs are going to do something exceptional in the countryside or whatever. It’s got to be everyone as an industry moving to a very different place. And that’s quite a challenge.


Will  3:07  

But how long have you been in this space for to give us an idea of experience?


Jae  3:12  

So my first house I did that would be called the Passivhaus Standard, which is a German standard, which is just very, very energy efficient. It’s the highest energy efficiency standard in the world. First house I did was 2010. And before that, I went and I did a Master’s Course because I was an architect. And yeah, I kept hearing all this you should do this sustainably and that sustainably and I really was confused myself. What do people really mean? Is it thrown around as a term? I felt I needed to take time out and I need to work out for myself what a sustainable practice might look like. I came across this standard during that process and I thought this is it. You know, we must have energy – number one, we must have energy efficient buildings. It’s the only way because we’ve got to have um, I’m sure you do talk to people may be very interested in the energy grid and having a renewable energy grid and zero carbon zero carbon energy. But in order to make that work, you’ve got to reduce the demand for energy, right down from what it is now. So match the demand to make the grid work. So that means the houses must be really energy efficient, so they match properly to that, to a zero carbon grid. So it’s absolutely critical. There’s no, there’s no negotiating. And then the other thing we’re interested in is embodied carbon. So that means that you’re building out of low, minimally processed materials. [inaudible] houses, I think, and the UK climate change committee said this as well, our future housing should predominantly be built from timber frame, because the amount of carbon embodied in timber frames is so much less than masonry.


Will  4:57  

Right. Do you predominantly build new builds or so you also retrofits builds within the price?


Jae  5:03  

Well, my first project was a mix of retro building, retrofit and new and it made me realize how challenging it is to do a retrofit, quite expensive. And it’s not just superficial, it’s really gutting the building, and to do it properly. So I think it’s still a big ask to make it economically feasible for people to properly retrofit the sort of standards I’m talking but if you’re doing new housing, it is the uplift in costs to go from what we currently do. What we need to do, you can do it really within six to 8%, probably even down to 4%. When we get into the market, right? So that uplift is economically sustainable, you can do it, so we should do it.


Will  5:44  

Sorry, what do you mean by 6 to 8%?


Jae  5:46  

Well, so if I was to build a house in the way that I build it with a timber frame and just mail me to building control standards, sort of what is minimal compliance and how to uplift it to net zero carbon I can do that in our system about 6% more for that new house. But that’s nothing for the gains that you get, you get really low bills, really super indoor air quality as health benefits if you were challenged with low income and the cost of energy, it’d be be fantastic for you. It puts all these gains [inaudible] you get lots out of it. As well as of course we’re mitigating climate change.


Will  6:30  

Yeah, let’s put that in perspective. £100,000 house it that’s an extra £6000. You’re looking at probably in the region of about one and a half to £2000 for energy of that house. That would be very low plus all the other-


Jae  6:45  

Yeah. And if you and if you took into account the payback of the low energy bills over the year, so if you were going to sell that house, you’d get that money back wouldn’t you when you [inaudible] that in loads of things you can do to minimize that uptake. You can design it carefully. You can do something like [inaudible], which is the shape of the house, the proportion of the envelope, the thermal envelope of the house to the floor area, you can get a really efficient house where it might only be the ratio might be around two, or you could build a house where the ratio would be four. So one, that’s two would be like a terrace, I mean, the perfect shape would be a sphere or cube. [inaudible]system from going from the perfect shape, this wiggly-giggly shape, it could cost you twice as much to build your house. So there’s lots of weight and also there’s a huge cost difference in how much glazing you have and stuff so, it’s educating people how they can do it economically, just through design careful design, and really do it for a minimal uplift. And then they can have all those those sort of basket of benefits as well, as well as feeling they’ve done the right thing by the environment as well.


Will  7:51  

And we hear about different types of insulation and are there particular types of insulation that people should be aware off? Because I remember we were talking for my cousin’s husband, Charlie Luxton. And I remember him telling me about, if it’s out of 10, say, normal kingspan is usually about six out of 10, maybe seven out of 10. And I’m obviously going to get this slightly wrong, because I always do, but I’m not quoting him directly, but say six, and then it’ll go down to about three out of 10, after about 10 years, and it’ll slowly go through. But then if you have some very natural insulation, it’ll start off at five and a half out of 10, or six out of 10. But it won’t actually go down to anything below five. So therefore, its thermal value will actually over the long term be much more efficient and won’t emit any of the chemicals.


Jae  8:48  

Yeah, I mean, I don’t know about about deterioration over time. I wouldn’t have thought they’d be – I haven’t heard of there being deterioration with chemical paste insulations, but you might be right. I don’t know any facts. But what I would say is the facts that I know are, if you’re choosing a closed cell insulation, which is basically made out of oil or plastic, it’s come from the oil industry. It’s a waste product oil industry, so they love to sell it. And huge companies who sell those products, things like celotex, and stuff like that. And while it’s very high in body carbon, it might be an insulation, it might save you some carbon when you install it. But to make it, they’ve had to emit a load of carbon into the atmosphere, and it’s the atmosphere that’s it, isn’t it? So have something called a sips panel and build your house, which is two bits of board with some of that closed cell insulation between, it’s cheap, embodied energy is surprisingly high. Whereas if you build uh put, natural installations like sheep’s wool, or just wood fiber, recycled newspaper, or they don’t have quite as good a thermal conductivity, they don’t perform quite as well, so you need a bit more of it, but they’re not expensive and they’re very low in embodied carbon. And as long as you’re getting the wood from a sustainable source, which you should be doing [inaudible] ultimately. And actually, the interesting thing is the RIBA, that’s the Royal Institute of British Architects, bought out something called the RIBA 2030 Climate Challenge. And they’ve got targets in there for architects to sign up to. So basically, by 2030, you’ve got to hit a target for operational carbon, that’s amount of energy your house needs every year to hit that target. And basically, that’s the Passivhaus standard. And then underneath it, they’ve got a target for embodied carbon. So you’ve got to build your house carefully as well with the right sorts of materials. And that’s never happened before. We’ve never had anybody telling us that we have to be careful about the embodied carbon, the things that we make things out of. So I find it incredibly – I will – I for a long time felt it was important. Now we’re getting the feedback. We have to we have to build with low embodied carbon material. So that means natural insulation is the way to go. The other thing I’d say about natural insulations is, they behave much better in terms of moisture. So they generally – they’re like natural aren’t they – manage moisture in a way that an oil based insulations completely inert won’t. So if you’re going to make it in the house, you should in my strong advices, you should match that natural insulations because you need moisture you need- your house needs to breathe. It’s got nothing to do with energy, but it needs to be safe, otherwise it will rot. You make sure that your house is designed in a way that allows vapor, moisture to move through and dry out as it needs to seasonally. And using all these plastic insulations is a no no, really, if you’re very careful. It’s fine if you’re doing masonry because it’s all inert, isn’t it? A brick is in a [inaudible] in a you know, thrown- this is what we’ve done, we’ve just thrown lots of high embodied energy buildings into our [inaudible] like we haven’t cared. The final thing I’d say about the insulation is that people are cutting them and dealing with them on site, people actually have to do the work. I don’t think it’s best working with and breathing in. So I think it’s much healthier and kind to the pitch of the guys on site [inaudible] on site, if they’re working with more natural, less processed materials is the nicer [inaudible].


Will  12:20  

With this new looking at embodied energy, looking at how to build a building, are we going to see the big house builders going down this route? I mean, is it going to be legislation or, you know, or is it just recommendations from RIBA?


Jae  12:36  

That that is a very good question. And it’s been a problem all along. And I’m sure it’s in lots of areas it’s a problem. So in the UK we’re very unusual we have, I think seven large volume house builders [inaudible] market and they have huge lobbying power and they lobby against change because they make you think of the profits Simmons made last year one is all a hoo ha, so it’s that that resistance to change, and someone in government has to be strong, and insist that it does change. And the head climate change committee issued a report last year, and for the first time, I agreed with everything in it. We must do these things, we must hit these standards, we must do it in the next few years. You know, we must have low embodiment, we must build out of timber so that they’re saying all the right things. That’s the UK [inaudible] change committee so, eventually, the next building could drop. The sad thing is building control, the English ones that are coming in now, are worse, frankly, than the ones we had before. [Inaudible] wrote letter complaining about that and saying, you know, it’s just ridiculous. But they’re talking about the next one, which might be, I don’t know, maybe three, four years time, they’ll suddenly do a big step change. And I hope they will. And I hope government has the guts to do it because all the evidence says we must do it and we must do it quickly.


Will  14:00  

So with Brexit, we’re seeing worse legislation on house building.


Jae  14:05  

I don’t know whether it’s Brexit influence, or it’s just the same old story that government is influenced by business. And the business that dominates is big business and not very, it doesn’t have the conscience, does it? I don’t think all people in it that are awful, I just think sometimes for big corporate businesses, it’s the nature of big business, or maybe it’s the nature of the capitalist system, and this whole ideology of we’re not going to interfere in the market. Well, we have to get over that we have to interfere in the market. And of course, we do interfere in the market when we choose to and we want to. You think how often [inaudible] we can’t possibly do that, you know, it’ll affect profits, it will, uh, in the end we just need to think of all the floods recently we’re going to cost ourselves a lot more [inaudible] and one of the shocking things is if every every year we delay change, the mitigating strategies get bigger and bigger and bigger and cost us more. Every five years, we put it off, you know, you see the mitigating strategies, amount of work they have to do increases, increases, increases, we really need to do it now.


Will  15:11  

And people listening to this will be working in and running buildings that are already around. I mean, are there some quick tips that you can give to I know that you’re saying that it’s actually very costly to retrofit buildings, but in reality, we’re not going to be knocking down every single building in the UK and re rebuilding them. So we are going to have to work with what we’ve got. And I mean, what is it that people can do in buildings and in your own homes as well?


Jae  15:46  

Going to existing buildings is the most difficult task-


Will  15:49  

Right [Will laughs] Sorry


Jae  15:52  

equivalent standard to what I do for new build so it’s something called enefit and slightly more lenient, then a new build, but it’s basically focusing on the energy that you use the heat energy. So if you take a house, least 60% of the energy of that house will be to do with your space heating, keeping you warm. So that’s the big hit. The second one is hot water, but the massive big hit, I did a pie chart for you, you see a huge section that would do your space heating. So it’s getting that down. And to do that, we’ve got to get this type of efficiency up. And it’s insulation, and it’s stopping leakiness that’s the thing that people so people get the idea that they got to put insulation, but they don’t necessarily get the idea they’ve got to stop all the leakiness. So in a new build, to give you an idea, you’re allowed to have one cash register holes in your house. Imagine that ATM. Yeah. And with the fact that people build poorly in this country, so we often build it twice as bad as it should be, tests will suggests that you might have two ATM worth of leakiness in your, in your new- with what I do, you’re allowed to have a credit card with holes. Now in a, in an old house you might have [inaudible]. So that’s the really significant thing that you have to deal with and it’s very hard in an old building because those holes will be in your [inaudible] under your bath. You know all very inaccessible places very few places where all the joist ends go into your brickwork. And so there’s a lot of fiddly work. And then also, you start interfering in the building and it’s sort of managing its moisture, probably at least you know what it’s doing. If you do something wrong and put the wrong sort of insulation in the wrong place [inaudible] could cause a problem in your fabric, you could start getting mould, and you could start getting, mould and rot. So you really do need somebody who knows what they’re doing, to help you. And they can do it really well. But because it’s so fiddly and so invasive, that’s why it’s expensive. And what they have done is created a way to do it is to do step by step they call it. So you basically get someone to do a plan for you and eventually end up at enefit, standard [inaudible] it all perfect. You do it oh five or 10 years. Know where you’re traveling to so you’ve got a finish end. Step one might be- and what they do is they that that person knows what they’re doing will make sure that it’s step one, doesn’t cause you any problems to step two, so you don’t create any unforeseen consequences as you step through and step up to the final. The only way to do it really because very few people have massive- but some people might do but yeah, this step by step approach is a very good one. But maybe the government has to invest in actually subsidizing people to help them do that as well because it’s not really individuals problems is it? It’s our whole [inaudible] culture so I’m not keen on putting a burden on individuals to be responsible. I think the organizations and governments need to take responsibility, and that means they might have to provide a lot more help than they aim to do now when they provide no help and I actually do think they’re gonna knock down a lot more than you do at the moment.


Will  19:43  

That’s in- I mean, that’s interesting in itself, isn’t it with planning laws and the way people want to preserve old buildings and older buildings for the look but yet, actually is that the right thing to do? Should we be changing?


Jae  20:04  

I mean, obviously, we do want to keep some buildings, but, you know it’s, maybe only the ones that we really think are worthwhile, you know, maybe we need to be a little bit, you know, a bit braver about saying, actually, we could build much, maybe denser and really good quality housing, and set a much better economic price point and be a bit more brave and inventive. And, you know,


Will  20:30  

I agree with you that I’ve got to say there are some very, very ugly buildings that are kept. And they shouldn’t be because it’s made of concrete and looks like a toast rack does not mean that it’s a nice building.


Jae  20:46  

And we have this sort of bit of a backward looking thing along the past is better, we must maintain it But no, I think we have to be brave sometimes and actually got to create a future haven’t we? Yeah, in a way we haven’t got a huge choice now we’ve got ourselves into the mess we have.


Will  21:02  

And are you seeing an up- because you work with housing associations, don’t you? And are you seeing an uptake in people’s talk? And has it increased over the last year or so?


Jae  21:16  

Yeah, definitely. When I started off nobody even heard of the idea of Passivhaus which is this energy efficient fabric [inaudible] people look out for it, they’ve heard of it. The people who ran the scheme that won the RIBA Stirling Prize, which is the highest prize in architecture. It was a Passivhaus social housing scheme in Norwich that Norwich City Council built that won the RIBA, that’s unknown. They usually high end art, you know, really expensive, you know, [inaudible] and this was like a scheme for affordable housing, but to a very, very high environment. And that’s amazing, you know, so things are shifting and the RIBA have put this standard out [inaudible] architect’s declare a climate crisis that a lot of architects signed up to sort of sign it. My local council has just signed up accepting it as a climate crisis. Well, when I started 10 years ago, nobody would have known what I did. And, you know, it was very, yeah, it’s really changed over 10 years. And and you just the fact that you hear all the stuff on the news, don’t you all the time? Very few people are being skeptical. I think that it’s much more people accepting that we are in a crisis.We [inaudible] the impacts can’t we now much more.


Will  22:39  

I think so. I think so. But I still do- and I’m just voicing an opinion – I’m still slightly worried that you, you know, we’ve got councils declaring climate crisises, but what are they going to do? So easy to “I declare a climate crisis” and then someone goes “What are you gonna do about it?” “I haven’t I haven’t got a clue [inaudible] that I’ve declared”


Jae  23:10  

Exactly, i absolutely agree with you. The local council I thought this is this is they declared this this is my my opportunity to write to the counselors and say, well, this is you want to do some education now you know do you want to look at what this means how you can do net zero carbon houses, and they wrote me back an email that was so crass and lacking in knowledge and not taking up the offer. And I wrote back and you know, I was really irritated and saying it’s, you know, you’ve done the easiest thing in the world to declare that you accept there’s a climate crisis, it’s a whole other thing to do a practical outworking educate yourself to actually what’s required, and do it, you know, tell that you’re not the greenest borough in London. It’s just nonsense, isn’t it? And same with objects. We do. CPD started doing more this year. And I think that’s driven by the RIBA doing this target challenge. And at the end of it, I say that you’ve signed up to this thing and now you need to sit down and you need to write out how you are going to transition from where you are to this net carbon commitment that you’ve made an actual practical plan, you know, over the next five years, what are we actually going to do?


Will  24:25  

I guess we’re, we’re varying on different different subjects now. But I think both of us come, we both come from the same place.


Jae  24:33  

It is very important, isn’t it? Because [inaudible] transition and everyone’s got to transition and they’ve got to be real about it.


Will  24:39  

Yeah. And I think that’s what this podcast is about it’s trying to, I mean, I’ve been doing this now for coming up to 20 years. I’ve seen enough rhetoric and enough greenwashing over my years to know that actually, I’m now slightly too old in the tooth to actually care about um listening to someone say that they’ll do it, when I kind of just want to hear about how they’re going to do it.


Jae  25:06  

Yes, yeah.


Will  25:08  

And it’s about talking to people. And it’s about understanding what other people can do. And I think we can all learn off each other. And we can all try and understand what-


Jae  25:17  

I’m very, you know, one of the reasons we set up and we bring it round to the business, actually, nicely is why we set up Pascal’s phones, I’m in business with a with a contractor or a builder carpenter. So I’m an architect with a builder which is very unusual combination a very good one. But we both agreed, what needs to be done, you do it? Yeah. Build the houses, you’ve got to prove that it what the price was, you’ve got to show how the energy reduction was, you’ve got to put those examples out there, and then the arguments are done aren’t they? When the house builders say, oh, I can’t do that. I can’t make money. It’s not economic, you say, well, look, you know, experts over there are doing it and they’ve done it for this price, you know, and then conversation stops, doesn’t it? Yeah. Doing things and building things and [inaudible] things are what it’s all about.


Will  26:04  

The proof is in the pudding. As a business do you travel? And I’m just understanding how you manage your own environmental management as a business as well? And does it seep into your actual way of running the business?


Jae  26:20  

Well we’re really still quite a small company. So we don’t have our own lease our offices, you know, we don’t have our own offices. I’d love to build my own Passivhaus office, if we have the chance, I’m sure we will at some point, and we will do it to the standard that we build elsewhere. If we were doing it and travel, we don’t need to travel that far. We use Skype all the time, which is fantastic. And use trains [inaudible] trains, isn’t it? In terms of all the products we sell on our online shop, you know, all houses all low embodied carbon and all the businesses that we go into partnership with, they’re always people who’ve carefully chosen got high environmental credentials, and actually it’s just a pleasure to do business with them, I mean, this is one of the things I’m not actually an optimist, really, you know, I’m not convinced that we will be net zero carbon by any of the dates that people say. But I find doing it improves your quality of life. I’m a happier person. I [inaudible] nice people, I have interesting conversations. I get that out of it. You know, I know I get the satisfaction of building really great quality houses and not crap.


Will  27:33  

Well it’s it’s been really good talking to you and understanding more about how and what we should be doing from a Passivhaus and understanding how and what we should be doing building houses. So thank you so much for today, Jae, thank you so much.


Jae  27:49  

Thank you very much for chatting to me.


Will  27:53  

Thank you so much for listening to the end of this episode of the green element podcast. Do take a moment and share this with your friends and colleagues and rate and review the podcast. Wherever you get your podcasts. I’d love to know what has been your biggest takeaway from this conversation? What are you going to do differently? Please share your thoughts across social media and tag us so we can see them too at g_podcast for links and show notes for this episode, visit our website, greenelement.co.uk/podcast. Thank you again. I hope you will join me on the next episode and together we can help create a better world.


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