Juraj Mikurcik self-builds a gem of straw and wood that demonstrates everything there is to love about Passive House design.
In a recent post we noted that Juraj Mikurcik’s Old Holloway Passivhaus was nominated for a UK Passive House Trust award; here's a closer look. It’s what they call a “self-build” in the UK -- where owners manage the process themselves, from land acquisition to construction. Self-build is not for the faint of heart; read Ben Adam-Smith at House Planning Help if you really want to get scared.
Juraj has been working on his house for years, and moved in last July. As a low energy, super-insulated Passive House design, it doesn’t have much heating, just a small 4kW wood stove, and two bathroom towel warmers connected to the hot water heater. The dog on the chair probably adds as much heat as the warmers do. I certainly wondered if it was enough. Summers can also be a problem due to overheating, but Juraj writes on his blog:
We moved in last July. One of the early observations was the stable internal temperature of around 21°C, irrespective of what was going on outside. There was a spell of hot weather later in July with external temperatures reaching high 20s/ low 30s….In the new house with the large roof overhang and some external blinds we managed to maintain the internal temperature below 23 degrees even during the hottest periods. The thermal mass of the concrete slab undoubtedly helped.
But that was last year; this summer has been incredibly hot in much of Europe, and I asked Juraj how it was working out. He sent me this chart showing interior and exterior temperatures, and writes:
Hi Lloyd, we've been really pleased with how it performed in the recent heatwave. Outside temperatures regularly hit 25-27C (77-81F), but indoors it generally peaked around 22 or 23C (72-74F), with night purges bringing it back down to around 20C (68F) each night. We've been quite meticulous about keeping the windows shut when outside temperature got higher than internal temperature. PHPP predicted 0% overheating over 25C (77F) so it's been great to see that this has been achieved during the heatwave. I feel it's been a combination of careful window design, robust shading strategy, inclusion of useful thermal mass (concrete slab and clay plasters applied to straw and heavy Fermacell boards) and religious night time purge that all helped to keep the house nice & comfy. Seriously, at times it felt like coming in to an air conditioned space when the temperature and humidity was considerably higher outside.
It worked pretty well in winter too:
It’s all very well that the house is comfy in summer but what about when it gets cold out there? How are we going to cope with no radiators? Well, we needn’t have worried. As the season was turning colder, we were getting more and more ‘free’ solar gain from the lower sun, effectively balancing out slightly increased heat losses through the building fabric. It wasn’t until one evening in November when we lit the small wood stove for the first time. On average, we now light the stove for an hour or so every other evening, sometimes less often. As long as the sun is shining, the house maintains the temperature beautifully.
What makes a Passive House design so comfortable is the Mean Radiant Temperature -- the walls and windows are so warm inside that heat is not drawn from the occupant’s body, which is the main reason we feel cold. The walls in Old Holloway are made of straw, prefabricated into ECOCOCON panels. This was the first installation in the UK, a brave move for a self-build project where you have nobody to blame but yourself if something goes wrong.
The video shows the three-day installation (warning: loud piano music).
The walls are finished inside with clay plaster, with a bit of “finely chopped straw in the top coat for a bit of sparkle .” There are many benefits to clay plaster; Juraj notes:
Clay plaster works brilliantly when applied directly to straw, as it allows moisture to permeate back & forth, effectively acting as a moisture buffer. It’s a healthier option compared to cement or gypsum plaster and will add significant thermal mass to the building – we have 7 tonnes of it to put on walls!
The exterior is clad in the material du jour -- Shou Sugi Ban or charred cedar. Juraj did it himself with a blowtorch; this is seriously time-consuming and very impressive.
Data nerds can be impressed with the numbers, but I am impressed with how warm and comfortable and inviting and big this 1,022 square feet of house seems, and the use of natural, healthy materials with low embodied energy. I am envious of Juraj; as an architect, I hated every building I designed (which is probably one reason I quit). I am writing this post in a cabin I designed and want to tear down. I do not think I could live in a house I designed without complaining every second. Juraj tells another story:
But it’s the other qualities of the house that we appreciate the most: the combination of open plan living and more intimate spaces, the sun rays shimmering on the soft clay plaster, the acoustics, the ability to accommodate big parties of friends, the luxury of being able to sit next to the large glazed window without feeling uncomfortable, the magnificent sunrises, the raindrops falling from the crinkly tin roof. We just love watching the world go by, whatever the weather.
This is the true wonder of Passive House design. Data are important, but luxury and comfort are the end result.
As a side note, the mechanicals were designed by Nick Grant and Alan Clarke, seen hard at work here. Nick is known to TreeHugger for his principles of Radical Simplicity, which were practiced on this house.