Passivhaus in the Woods Is Totally TreeHugger

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Updated March 23, 2019

It's compact, simple and mostly wood. It's also amazingly airtight for energy efficiency.

The cover of the latest issue of my favourite Passivhaus magazine made me smile, and architect Juraj Mikurcic wondered what I would make of it:

Juraj built his own wonderful Passivhaus and works with Architype, my favourite UK Passivhaus architecture firm, who designed what I still think is one of the world's greenest buildings; Matt Hayes of Architype tells David Smith of Passive House+ how Fishleys Passivhaus fits into the environment.

The owners wanted it to feel like a retreat in the woods as they both love woodland very much, so it has no relationship with the road. We tested views from all around the site and it was well-sheltered by the woods.

© Matthew Ling Photography for Passive House +

It certainly is a TreeHugger. Matt continues:

The house is seamlessly bedded into the woods and the route through the woods from the road is impressive, I think. As you get closer to the house, you see the striking red door set against the green of the woods.

© Matthew Ling Photography for Passive House +

There is a lot that is TreeHugger in the planning of the house too. The owners both work from home now, but want to be able to age in place, so the studies can convert into bedrooms and there is a wet room with concealed knockout doors that can convert into a fully accessible bathroom. And then there is one feature this TreeHugger loved:

One final stipulation from Liz was to avoid the trend for open-plan living. She wanted the kitchen to be separate from the living space, ensuring noise, smells and mess were hidden away.

© Matthew Ling Photography for Passive House +

The owners also made it as "efficient and flexible as possible." They probably got an earful from one of the Passivhaus consultants on the job, Nick Grant of Elemental Solutions. Nick makes a very persuasive pitch for simplicity of design, and you can see a bit of that in the Fishleys Passivhaus. Alan Clarke did the mechanical and electrical, as he did for Ben Adam-Smith's house.

© Matthew Ling Photography for Passive House +

A lot of people are building with prefabricated panels these days, but builder Mike Whitfield wasn't having it. He tells David Smith:

It’s more expensive to use prefabricated as long as you have the expertise to do it efficiently yourself. [But] if you have carpenters stumbling around on their first passive house, a factory product might be easier.

© Passive House +

Passive House+ always has a box with the cost of running the joint, and this is pretty low. Today this is US $45 and thanks to Brexit, it may soon be 45 US cents. But people don't build Passivhaus for the savings. Owner Mike Hill says:

We’re very happy here. Last summer, when the temperatures were so high, we had a nice comfortable working temperature all day.... We’re also passionate about ecology, growing our own food and taking care of the environment, so the passive-house lifestyle suits us.

Designers Archtype have built buildings out of such healthy and natural materials that I have called them almost edible, and they have done that again here; the insulation is Warmcel cellulose, with Steico sheathing and clad in Douglas fir. Instead of a high-tech membrane, the interior moisture and air control is done with SMARTPLY PROPASSIV, an oriented strand board (OSB):

The integrated vapour control layer and air barrier properties eliminate the need for additional Air and Vapour Control Layout (AVCL) membranes. The coating also provides a smooth durable surface for superior bonding of airtight tape at panel joints.

The stuff obviously works; the air tightness came out at 0.13 ACH at 50 pascals, which is ridiculously low,"and one of the best results ever published by this magazine — especially impressive given the complex shape of the house."

The wall is almost entirely plastic-free. There are ten inches of EPS foam under the ground floor slab, but that's a good place for foam, where it can't burn or shed flame retardants and the alternatives cost the earth.

In the end it is a lovely house, TreeHugger in its design, planning, and construction. Thanks to Passive House+ for sharing it with TreeHugger; lots more to read about it on their site and even more if you subscribe.