Katherine Martinko is an expert in sustainable living. She holds a degree in English Literature and History from the University of Toronto.

While researching the corrugated hemp panel that went into the marvelous MONC eyewear shop in London, I followed the trail to Margent Farm, described as being "just outside Pidley, a small village in Cambridgeshire between Huntingdon and Ely" in the United Kingdom. There, on a hemp farm owned by former film director Steve Barron, the hemp panel is used to clad Flat House, designed by Paloma Gormley of Practice Architecture.

The panel itself is fascinating, but what is behind it is a marvel. The building has a simple form thanks to planning rules that preserve the shape of the pole barn it replaced. But it's likely that Gormley might have designed it this way even had there been no restrictions because inside and out, it is a model of simplicity and restraint.

In a long interview with Rob Wilson of Architects' Journal, Gormley explains: "The design is driven both by the choice of material and the construction rationale. Our starting point was the raw materials from the farm. The body of the house is entirely made of materials that have been grown."

I have often written that when you look at the world through the lens of embodied carbon, everything changes. And indeed, this house changes the way one looks at how houses can be built or, in a sense, grown. Gormley has designed a house that she describes as "radically low in embodied carbon."

The most notable feature of the interior is the exposed hempcrete—a mix of hemp shiv (the chopped up, woody core of the plant) and lime. She tells Architects' Journal that the hemp was grown locally. There is also a half-inch thick sheet of Panelvent sheathing with high racking strength to stiffen up the structure, but that also is vapor permeable for "breathing wall" construction. Then there is a 5.5-inch thick layer of STEICO wood fiber insulation.

However, if that is not enough, it is all prefabbed. Gormley explains: "The building is composed from a panellised system that we designed with a mind to scalability. Hemp construction is limited by the seasons, because you can’t cast hempcrete out of doors in the winter. The panels are factory-made and dried off-site so construction can take place at speed and year-round." The panels were lifted into place in two days.

As we have noted, the walls are designed to breathe. This contradicts much of what I have written in the last few years since I fell in love with Passive House and wrote articles with titles like "Should We Be Building Like Grandma's House or Like Passive House?" I have become a devotee of the Passive House, but the Flat House is very much a Grandma's house, built out of local, natural materials with walls that breathe.

There are many who might argue that point. In particular, Juraj Mikurcik, located 150 miles away in Hertfordshire, who built a Passivhaus out of prefabricated straw bale, wood, and clay. But then this is even simpler, described by Gormley as "a low-tech approach and bio-based materials can be combined with off-site construction to create a scalable low-impact, beautiful architecture" where "the orchestration of natural materials creates a building that regulates humidity, temperature and air quality without the need for ducting or equipment."

Certainly, from an embodied carbon point of view, this might well be as low as we have seen. From an operating carbon point of view, it gets its energy from a biomass boiler. Some would argue this "fast" carbon emitted by burning biomass still has a negative impact. It's all very complicated.

What isn't complicated is the design of the interior. Gormley describes it as sharing the methodology of Tudor construction, where one infills between the structural elements; you see the wood, and the hempcrete is set back, with only a thin coat of clay paint. The hempcrete absorbs sound, and "the absence of reverberation creates an acoustic intimacy and sense of being held by the space."

Whenever I have written about insulations, readers have always asked, "Why don't you ever talk about hempcrete?" In fact, we have, but it has been hard to get in the U.S. where growing industrial hemp only became legal in 2018 and is not yet in the building codes. It is one of those natural materials that fall in my category of building with sunshine. The whole house was grown rather than built.

But another factor is that the few hempcrete buildings I have seen in North America have that sort of hippie aesthetic we have always avoided here on Treehugger. The Flat House pushes all the aesthetic buttons as well as the environmental ones. There is much to learn from this.

Plans and lots more to read at Architects' Journal.

Wilson, Rob. "From farm to form: Flat House by Practice Architecture." Architects' Journal, 22 Jun. 2020.

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