Why aren’t passive houses (AKA Passivhaus) mainstream? Why isn’t every new home built in the UK produced to the design specifications of passive houses?
Here I’ll go through what’s bad about passive houses, whether it’s true, and what might be done to fix the problems.
1) Passive Houses are boxy and ugly
Passive houses are designed with “Form Factor” in mind during the design phase. Read about how to calculate the Passive House Form Factor here. The Form Factor is, honestly, how boxy the house is, as it relates to the total surface area of all of the external walls (the Heat Loss Area) divided by the total floor area. A lower number means there’s less surface area for heat to escape. A normal detached house is about 3, which is good.
The rule is: halve the Form Factor and you can halve the insulation thickness to get the same output.
Here’s an example of an apartment block at 1.75:
1.75 is a great form factor – passive house people love that low number, even though it’s an ugly building. Now look at this building:
It’s got more surface area for heat to escape from (so it will require over twice as much insulation thickness as the block of flats).
As such, Passive House designers will hate it, even though it’s aesthetically beautiful.
Although Passive Houses have to obey stringent design specifications to achieve their energy efficiencies, they can still be beautiful, as this one shows:
2) You can’t open the windows in a Passive House
This myth is born from the super-high levels of airtightness that passive houses need in order to retain heat that is lost through draughts in normal homes. Passive houses also use Mechanical Ventilation Heat Recovery Exchangers for ventilation, further fuelling the myth that opening the windows will break them.
Of course you can open the windows in a passive house. Firstly it’s a requirement in all modern homes for windows to be a form of escape in a fire, so they legally have to open. But more than that, sometimes you just want a nice breeze coming in through the house on a hot day.
More importantly, with passive houses the MVHR unit guarantees clean, fresh air in the home without opening the windows – this is great during cold days, when the last thing you want to do is open a window to let cold air in.
3) Passive Houses are more expensive than normal houses
These days the homes we see built to passive house standards are only five to ten per cent more expensive than Building Regulations homes (which are the worst-performing buildings you can legally build, remember).
If a Passive House costs an extra 10% on your budget initially then you’ll make back the savings within about ten years – and you’ll have lived all of that time in supreme comfort. Past ten years and you’re actually saving money from the cost of the house – a great feeling.
4) Passive Houses are airtight, so they’ll get stuffy and moist
The MVHR units in all passive houses guarantee the supply of clean, filtered and warm air (even in winter) at the levels all humans need to be healthy and happy (30 cubic litres an hour). MVHR units remove pollutants, bad smells and moisture from the air automatically. They are super-cheap to run and very quiet, too.
Compare this to normal UK homes which rely on noisy, greasy ventilation fans in the bathroom and kitchen and trickle vents in the window frames. They make air stale and stop moist air from escaping your property, which causes mould and health problems.
Here is the physics behind how Passive House clean air ventilation systems work.
5) No-one can get the MVHR systems to work properly
This is sadly true. Lots of big developers have failed in their flagship Passive House projects to correctly monitor the installation and commissioning of their MVHR units. There are many other examples of MVHR units not working properly.
It is crucial that before any MVHR system is installed it is designed to consider occupancy habits, moisture levels indoors, necessary airflow rates, pressure drops, air resistance and acoustics.
Once it’s designed it is crucial it is installed by HVAC technicians that understand how MVHR units work. The air will leak if they crush the ductwork, use glue to connect the ducting or bend the ducting too much.
Properly installed, an MVHR unit will match its detailed ductwork design and it will work properly. Hundreds of thousands of MVHR units work perfectly on the European continent, so it’s not a problem with the technology, but how it’s installed…
Our team knows how to design, commission and guide the installation of high performance MVHR systems to ensure they are super-quiet, energy efficient and deliver exceptional levels of home comfort and healthy indoor air. Please contact us via the Contact Page to ask a question, or submit your plans for a free MVHR sizing and specification proposal if you have a build project you’d like to investigate MVHR for.
6) There are no builders or architects skilled in Passive Houses in the UK
There are a handful of really good passive house builders and architects in London, a few more in the north and Scotland.
There are also lots and lots of builders and architects in the UK that tell you they know everything about low energy design and that “passive home thing”. They either greenwash the project or they discredit it and tell you they prefer their way of doing it. And that’s why we have 80 years of leaky, cold homes and high energy bills in the UK.
7) Passive Houses don’t suit the UK climate
In winter the MVHR system will keep the internal temperatures of a Passive House to a warm and comfortable 20DegC with ease. In summer, as long as overheating calculations have been made and there’s not too much south-facing glazing, a passive house in the UK summer will stay cool and comfortable.
8) Passive Houses don’t raise the price of the house when it’s re-sold
As the eco movement grows it’s likely that people will start to target homes that have good airtightness, proper insulation and are built solidly – as all passive houses are.
One of the reasons that people don’t buy passive houses in the UK is because the people that build them usually live in them for the rest of their lives.
In the UK we’ve been conditioned to believe that spending thousands of pounds a year on heating and electricity is normal. Passive houses can break this trend.
9) Passive Houses are too complicated to build
Builders and architects might convince you that passive houses are too complicated to build. They require prior design on areas such as insulations levels, airtightness barriers, windproof membranes and windows positioning and potential overheating issues in the summer.
But shouldn’t your architect and builder be considering this anyway? Isn’t that what you want from a professional home builder; an idea that they’ve considered all the potential issues that might arise when you live in the home.
Passive House design provides a natural framework for self-builders throughout the design and build process. The level of detail in the design process follows naturally into the construction period – airtightness strategy is mapped and identified, wall thicknesses and services penetrations are already finalised.
On Grand Designs, most of the projects break the budget when they over-run. With a passive house design you map out all of the dependencies ahead of time, so the construction process is smoother – and cheaper.
You’ve mentioned passive houses in the UK and how it helps with heating and electricity bills over the long run – giving the impression that it is only suitable for buildings in colder climates. What about tropical climates?
That’s an interesting question, Michelle, thank you.
Passive Houses in hot countries – for example, Malaysia – would work in the same fundamental way. High levels of insulation and airtightness would keep cool air inside the home, much like an ice box you might use to store cans of Coca-Cola during a picnic in the park.
An air-source heat pump could be reversed to become an air-conditioning unit delivering cooling air to the home, and an MVHR unit can provide fresh, filtered air into the property with a cooling coil to make sure you have a healthy supply of air. The MVHR system could also monitor moisture levels in the home to ensure it doesn’t get too sticky. You would also need a significant amount of external shading over your windows to ensure the solar gains weren’t too strong.
In a hot country such as Malaysia or China with poor air quality, Passive Houses could be very successful, especially as they filter the air that’s coming into the home so it’s purified and clean.
There are examples of warm-climate passive houses in the south of France. If you would like to visit one please let me know and I will send you the details.
I have built a passive house. It was not expensive and was easy to build. The right architect and there are more of them that can do this are out there.
Pros
My house is incredibly warm. You will not need radiators. In fact I only have downstairs UFH that I hardly turn on.
Cons
It can be hot in summer. I do have MVHR but this will not cool your house in summer. To be fair I do have a lot of south facing windows and solar gain. The house stores the heat. You need to think about the total design of your house. If you live in the south then do think about how your house will fair all season round and get energy calcs. forget about needing fancy wood burners. You will never use it in a passive house. I have the windows open in winter. I live in Surrey
Hi Jane,
It’s good to hear that your Passivhaus build was straightforward and not expensive – it goes to show that a low energy home can be built without a premium.
In the UK the focus during the initial planning of the home can be on the heating season, but as you say, we need to also consider the risk of overheating in summer (especially with the 38 DegC days). This is especially so for a home if there’s lot of south-facing glazing.
The key tactic to preventing summer overheating is also the simplest and cheapest to implement – don’t let the sun hit the windows in the first place! We can do that by fitting external shading, canopies or parasols, or having deeper inset windows into the reveals. Trees also help a lot in shading and cooling the home, and if they’re deciduous you’ll still get the benefit of solar gains in winter when the leaves fall off.
The next Passivhaus strategy to mitigate summer overheating is passive ventilation – opening windows on each side of the home to allow air to flow through and purge the warm air. The problem here is that hot days tend to be very still, so there’s not much wind about, plus it means that the indoor temperature will typically match the outdoor temperature.
Another thing to consider is thermal mass, particularly with basements. The ground tends to be quite cool a metre or two down, so basements will always be cooler in summer than above-ground floors. That can allow respite from the heat on the hottest summer days.
Anyway, I’m really glad to hear you’re enjoying your home, and I agree that fancy wood burners are totally unnecessary in a Passivhaus. I’ve always thought a fire pit in the garden is a good alternative, as you can use it all year round pretty much.
Best wishes,
Patrick
Hello Jane. I would love to talk to you about your passive house build in Camberley. I cannot find any architects in the area who are interested in designing me such a house or any suitable builders.
Hi Jane, Always good to hear of someone building to passiv standards. I have done the same. We have large south facing windows and no problems with summer overheating because I designed in a substantial roof overhang. I am delighted to report that in the middle of summer the sun just reaches the window sills but in winter streams into the south facing rooms and warms them nicely. Enjoy your home. Alison
I have read several times the MVHR unit takes moisture out of the air so mould wont be a problem. I have mould in both bedrooms but cant figure out why.
Any clues would be appreciated.
Hi Matthew, are you in a Passivhaus with an MVHR?
Mould can be caused by excessively high humidity in the air and/or very cold spots in a home due to cold thermal bridges. If the surface temperature of a wall, window or other building element drops below 13 DegC there’s a high likelihood that water vapour will condense on it and over a long period this can cause mould. I would have to know more about your specific home to help more though.
Feel free to email me at Patrick [@] heatspaceandlight.com if you’d like to discuss more or send through photos.
Hi Patrick,
I am currently doing some research for a school project about Passive Houses and Sustainable housing, are there any sources and studies you would recommend me to have a look at? Your points were very interesting and you seem very knowledgeable about this subject matter.
Thank you
Hi William,
It’s great to hear you are keen to know more about Passivhaus – I think that continuing along this path will put you in a great position for your future career. Environmental and societal pressures mean we are only going to be making homes which follow the tenets of Passivhaus more and more in the coming years (airtight, high insulation, good ventilation, thermal bridge-free).
In terms of good reading, please see a link below that considers the “as-built” data from a number of Passivhaus projects now being lived in. This is important, as we need to know that what we’re building really works in reality:
Are the energy savings of the passive house standard reliable? Report
In terms of other reading options, plus the opportunity to visit some Passivhauses, you should sign up to the PHT email newsletter:
https://www.passivhaustrust.org.uk/
I also enjoy the blog “Treehugger” and their email newsletter, and they strongly endorse Passivhaus.
In answer to your question, all Passivhaus consultants and designers attend a two-week course (“CEPH”) audited by the German Institute, and take exams at the end. Typically they have had a few years of working experience, as a builder, engineer or architect beforehand. The best way to learn is by taking on a job in a Passivhaus design agency, so perhaps consider it for your summer months (after the Lockdown, of course).
Passivhaus has unique challenges, mainly in educating on-site construction professionals as to how and why it works, and the additional attention to detail it follows. It costs a little more to build, but the final output is much higher quality than our typical housing stock. The other issue is the handover to the home-owner: they urgently need to understand how the MVHR system works and how, when and why to change the filters.
I hope this helps. Let me know if you need any specific help, or want me to write on anything in particular.
Best wishes and good luck with your course – you’re on the right track for a great career.
Hi Patrick,
I must admit, PassivHaus is a relatively new concept for me, but there seems to be an awful lot to commend it, and I’m looking quite seriously at the possibility of a new-build PassivHaus for our next move. You mention that problems can arise due to lack of experience building and fitting to this specification – are you aware of construction firms with experience in this area in the North West (UK)?
Thanks
Hi Karl,
I’m glad you’re looking at Passivhaus, it’s built on solid building physics principles for a comfortable, energy efficient and healthy home.
My main recommendation wouldn’t necessarily be to find a specific Passivhaus builder (although I can recommend some – please email me at patrick [@] heatspaceandlight.com), but to look for a builder that ticks the below:
1. They’re willing to investigate how Passivhaus works, and generally have a good attitude to trying new things
2. They have a history of building homes with good airtightness values (sub 2m3hr/m2 @50Pa for their Air Permeability score – and they will often have certification of this)
3. They can price accordingly for the extra work required, or that you’ll take the extra work on yourself, as most of it is related to diligence rather than labour/materials (eg, airtightness boundary checking/fixing)
4. They’ve completed the Passivhaus Tradespersons course, or are CEPH-qualified
5. They are willing to use good sub-contractors for the heat pump, MVHR, building fabric design, etc
If you email me at patrick [@] heatspaceandlight.com I can help with finding specific contractors that are experienced in Passivhaus that we work with in the north west.
Best wishes,
Patrick
If you use sips they put the house up in a week or so. I used a company in Gloucestershire and had the panels put up and then they returned to pump in the cellulose at pressure.
Hi Patrick,
Not sure if this is still current but I am buying a passiv house in London and about to exchange contracts.
I was wondering as this was all new to me and the house is not listed in the Passive house org database does it need to be for certification. Also, the MVHR is a Zehdner (I think) is that a good make and would it be easy to maintain and repair. Should the system go wrong can it be easily replaced or upgraded?
Hi Blossom,
Yes, I monitor all comments to the website.
If it’s certified recently, it may not be on the database (yet). Gathering the data for certification can take a long time. But alos, developers sometimes label their projects as “Passivhaus” if it’s met the requirements, but not officially certified. The true proof of certification is if it has the Passivhaus plaque on the wall outside the home.
Have you searched for its address + Passivhaus on Google to see if there are any news articles about it? Even now Passivhaus projects are rare enough that they get a lot of attention from the press.
My two areas of interest specifically to buying a Passivhaus would be: does it overheat in summer, and has the MVHR been properly serviced and maintained (filter changes/external grille/cowl cleaning)? Zehnder is a very good brand and likely means it has a quality ductwork system, which is good news.
I will send you a direct email so we can discuss in more detail, and perhaps we can arrange a site visit to review the Passivhaus to see if any areas need improving/maintenance.
Best wishes,
Patrick
If it’s not got on the register yet chances are it’s not going to be unless you yourself go through the process of doing it backwards. Doing if ‘forwards’ is a right old job best done by the ph architect who designed and specd it and who knows the certifiers to use. It’s a paperwork/photo combo that is certainly best done from the beginning by the people who know what the institute in Germany need to sign it off.
Hi Patrick,
Great article; really informative! I’m also impressed that you continue to monitor & respond to comments – helpfully & thoughtfully – more than 5yrs after the post.
There is one major issue I can see with PH designs and would really welcome your thoughts. I know one of the considered benefits is that the house is a very stable temp, around the house & around the year, often with little energy input. However, that’s the opposite of what I look for between rooms, and I surely can’t be alone. In our home, we have workspaces, food storage areas, transit areas & some bedrooms kept moderately cool. However, lounge & rec areas are warmer. Bathrooms & the kitchen are cosy, almost hot. Conversely, I prefer my bedroom cold. Not for everyone perhaps, but there’s considerable evidence for improved sleep quality & duration in a cold (certainly not 20deg) & blacked out room. [NB: I wasn’t convinced at all by either until I tried both seriously, now I wouldn’t go back].
When I’ve raised the question with other specialists the usual answer is either PH isn’t for you then or just ‘open the windows’. That doesn’t really cut it. And I’ve seen many owners of modern homes (inc those built this year) suffering miserably trying to cool themselves in summer. ln heatwaves they’re buying multiple fans & portable aircon. Your comment on building regs being the minimum possible standard probably apply, but I’ve heard the same from a PH owners (maybe their home wasn’t built or designed correctly, I don’t know). I realise a heat exchange unit designed to reverse & deliver cold air are one answer. We’ve got 2 & have been using them reliably since the early 90s. We don’t suffer cooling issues anyway, in the old part of our 200+yo cottage, as it has clay lump walls with a lot of thermal mass and it stays pleasantly cool on the hottest days. The heat exchangers are only in 2 modern extensions. I realise on a new-build you could consider adding a basement, for the reasons you already gave. I’m a big fan (no pun intended) as in my old Victorian terrace even during a heatwave you could guarantee sub-18° temps in the cellar. However, basements are more expensive per m2 than overground space. Even more so in our area, which is clay (as opposed to chalky soil, say). This would require sufficient reinforcement to mitigate stress from water pressure, at greater costs. Anyway, these ramblings do lead up to a question;
Is there any way to efficiently transfer or swap hot/cool air between rooms – without needing external exchange units or just opening windows?
It seems that if a building’s at a steady 20° & I wanted the kitchen/bathroom at 25° – but bedroom at 15° – then some form of efficient exchanger between rooms should be able to achieve that? Or perhaps, by designing the house with heat zones. I’m assuming while the external shell on a PH is relatively airtight, internally it’s intended to be freeflowing. I’m really interested to know the design implications & possible solutions.
Final thoughts, I’m already assuming it would make sense upfront to consider siting bedrooms (or any room desired to be cooler) lower in the structure; towards the north & glazed accordingly. Ditto, maybe an upside-down design to take advantage of heat rising (also to improve daytime views). I notice on the continent (eg. DE) they make use of much larger roof overhangs, along with recessed windows. I’m assuming this is to take advantage of solar gain in the winter months, while protecting from direct sunlight in the hottest months. I’ve never quite understood why we don’t do this in the UK? Again, thanks for your article – I’m hoping you may be able to shed some light if you have time to reply. Best regards, Ollie
Hi Olly,
Thanks for your input, I appreciate the considered response. I still monitor the website as we are an MVHR design, supply and commissioning company, and we also conduct investigative and compliance pressure testing for homes and commercial buildings.
1) Thermal comfort in Passivhaus homes: although a Passivhaus is designed to offer a constant 21DegC air temperature all year round, this air temperature can differ between rooms depending on (as you’ve highlighted) the orientation of the room (north-facing rooms are cooler), smaller windows (less solar gain) and size of heating emitters, if any. A bathroom will often have a towel radiator to be warmer than the other rooms such as bedrooms, which may have no heating emitter. So a Passivhaus can have a range of temperatures depending on where you are (and if you have a basement, it will be cooler)
2) In summer, pretty much all homes overheat unless there is significant external shading. High thermal mass will help, as will the ability to vent out the hot daytime air in the evenings.
3) I can’t think of an efficient way to swap heat/coolth between rooms – good initial design of the home by an architect or building physics designer should consider rooms from the start – a downstairs bedroom is a great idea in summer, for example.
4) So in conclusion, yes: your bedroom should be downstairs, north facing with small windows and deep reveals / overhangs. It will be nice and cool and you’ll sleep well with a warm blanket.
Why doesn’t the UK have deep reveals and overhangs to prevent summer overheating? Because we used to have mild summers – but now we’re seeing our summers become hotter and hotter, we’re starting to take on a more continental philosophy. I predict it won’t be too much longer before our apartment buildings are designed with courtyards to allow passive stack and cross-flow ventilation.
Hope this helps.
Best wishes,
Patrick
Hi,
I am interested in a passive house in suburban Melbourne, Australia.
It doesn’t get as cold here and summers are warmer. Probably prefer to open windows outside of winter for cross ventilation.
Any insights, advice, warnings or referrals?
Thanks
Hi Immy,
Australia sounds like a dream compared to the UK.
A Passivhaus is about following five tenets of good building physics design and ensuring the home is built correctly and that evidence is recorded to show the builder has followed the design. Theoretically every home should be a Passivhaus in spirit, but the problem is that modern homes often have a performance gap between design and finish.
You can definitely make a Passivhaus work in Australia, and there’s no issue with opening windows in summer – in fact, it’s encouraged. The benefit of Passivhaus / MVHR is that if in summer there’s an outside pollution event (eg, high pollen) you can close the windows and doors tightly and still have good ventilation.
I don’t know anyone in Australia yet unfortunately, but there will be some Passivhaus technicians around, and we could look at designing the MVHR system for you at least.
Best wishes and good luck,
Patrick