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.