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Dundon Passivhaus – Prewett Bizley Architects

In the early 90’s a German physicist named Wolfgang Fiest was told by German building industry professionals that they had tried adding more insulation to buildings, but that it hadn’t had any impact on the building performance. This idea offended the physicist’s scientific sensibilities so much that he and a group of other physicists set out to figure out what the building industry was doing wrong and why they couldn’t create better performing buildings.

The team went through the various ways which heat could be lost from a building. The first area to address was heat loses through the walls, roof and floor. To fix this they created a compact design which reduced the amount of walls and roof to a minimum and added a good thick layer of insulation to these. They also ensured that the insulation was continuous right over the roof and under the floor with no weak points or thermal bridges anywhere.

The next problem was draughts. Even a gentle wind can literally suck the heat out of a building through gaps in the building fabric and through penetrations for pipes and wiring. To tackle this they developed systems to make sure the building was completely draught free, carefully sealing each part of the building to the next. After this was done they pressurised the building with a fan to make sure it had no air leaks through the walls, roof and floor. It had lots of opening windows but when they were shut they had to be totally tight.

The next problem was heat lost through ventilation. We all need air but every time you open the window during winter you lose a huge amount of heated air in the process. Luckily there is a clever type of ventilation system called a heat recovery ventilation system which can bring in all filtered fresh air you need while keeping almost all of the heat inside the building.

The final problem was windows. A huge amount of heat is lost through windows. Assuming you have double glazing the weakest part of the window is the frame. Here there was also a solution, high quality timber framed windows with an insulation layer. Because it was Germany they also went for triple glazing. They took care to ensure that most of the glazing was facing the sun and that the windows were installed to be continuous with the insulation layer.

Being physicists, they did the maths beforehand and they wanted it to work economically as well as technically. They worked out that if they could reduce the heating requirements enough they could get to the point where they didn’t need a large central heating system (which is a big ticket item), and could use that money to offset the cost of the windows and insulation.

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Passive House | Markus Merz

As predicted the building performed as the physicists had designed it. The inside temperature was stable at around 20°C all year round even when temperatures outside plummeted to -20°C, and the energy consumption of the building was 90% less than the average.

So the technical outcome was a success but perhaps what wasn’t predicted was how incredibly comfortable the building would be. With fresh filtered and preheated air supplied to every room, and stale air extracted from the bathrooms, the air quality was amazing. So too was the feeling of living in a space where the whole of the interior is 20°C. Normally in winter we constantly feel cold air running off windows creating draughts but in this house you could literally sit with your back against the window when it was snowing outside. Occupants could walk around in shorts in the middle of winter and every room was at the perfect temperature.

It turned out that this was a genuine triple bottom line outcome. Comfort was radically improved, running costs were dramatically reduced and energy consumption was slashed by 90% (incidentally the amount we need to reduce CO² emissions by to avoid the worst effects of climate change)

It took the team a few years to systematise the approach into the tool we now call the Passive House Planning Package but within a relatively short time others had adopted the system and the first few Passivhaus projects were built. The movement gradually gained traction throughout Europe and then the English speaking world. At this point there are now around 30,000 certified Passivhaus projects worldwide with more being certified every day.