A Japanese style tiny house that's Passive House

exterior with garden
© David Montigny

We love Passive House or Passivhaus, the incredibly efficient building standard that sets an absolute limit on how much energy one can use per square foot or how much air is allowed to leak. The trouble is, the smaller a building, the harder it is to hit those numbers because there's so much more surface area per square foot of floor.

However, on his website Passive House in Plain English & More, Elrond Burell shows how three very small projects do in fact make the grade and hit the Passive House requirements. One, the Castlemaine Passivhaus in Victoria, Australia, has been seen on TreeHugger before and to be honest, I found it problematic. We give so much coverage to Australian architects who take advantage of the glorious climate; I noted that "if I lived there, I suspect I wouldn't want to be bottled in like this, and prefer Andrew Maynard's approach to green building where you do design for natural ventilation and orientation, and blur the line between inside and outside." I didn't really think this was a good poster child for the Passive House movement. The second is a true Tiny House on a chassis, but I will wait until it's finished to cover.

Mizu angled© David Montigny

The third project, a small office in Bretagne, France for a Passive House consultant, is a stunning little gem. Elrond writes about Project Mizu:

The designer, Thomas Primault of Hinoki, lives in a Japanese style timber house and loves Japanese architecture. So naturally, as his Passivhaus consultancy business started to take off, he designed and built himself an exemplary new Passivhaus office to suit his taste.

Mizu evening© David Montigny

And indeed, it is beautifully proportioned, sitting in a zen garden. Surprisingly, all three projects are built without foam, going for an "ecological construction agenda," albeit with a few twists – Project Mizu has vacuum panels for insulation in the floor, and phase change material (PCM) in the plaster walls to act as thermal mass. This surprised me; I had thought that mass-and-glass was out of fashion, done in by super-insulation like that found in a Passive House.

Mizu interior© David Montigny

In fact, one of the things I love about Passive House is that it doesn't rely on high-tech things like phase change materials in the plaster, but instead a lot of insulation, careful detailing and as Elrond notes, "exceptional attention to detail and quality control during construction." However while PCM may be high-tech, it is simple and lasts forever. Traditionally, in warm climates with big diurnal swings in temperature, thermal mass has been used to keep things cool in the daytime. And hey, it's Easter, so we might as well celebrate Mass.

Temperature© Mizu

This graph shows the remarkable performance of a Passive House – in this case where there was a heat wave with the temperature swinging from 50°F to 86°F between day and night; inside, the temperature (yellow line) moves only 5°F. That's usually attributed to great insulation and high quality windows; perhaps the phase change material is helping too.

Then there is the heating system. The joke in Passive House used to be that you could heat it with a hair dryer; the new joke will be that you can heat it with a tea kettle. Because in fact, that is exactly what they do here, sort of.

teapot© David Montigny/ Heating system hard at work

Mizu is heated by an iron tea kettle that exceeds the heat losses. However, it is a fine balance between heating and internal gains in winter. Overnight and weekends when the kettle is not used, there are also no internal heat gains from people or computers. It was found that in the morning, particularly Monday morning, the internal temperature was as low as 17 degrees celsius [62.6°F] which wasn’t a comfortable a temperature to start the day. The solution was to install a small heating diffuser near the work space connected to the ventilation. This raises the temperature to a comfortable 19 degrees celsius [66.2] whenever needed.

zen garden© David Montigny

17°C is what my house is set at all winter; I would have left it to the tea pot. However like Elrond, I am excited about one feature of all three of these buildings:

It is also interesting, and heartening to me, that all three projects pursued an ecological materials agenda as well as Passivhaus. Where this can be adopted it is a winning combination for health and for the climate. Passivhaus is the starting point for Architecture in the Anthropocene, not the end point.

See them all at Elrond Burrell's website

Tags: France | passive house


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