Chestnut Farm Is a Modern Prefab That Doesn't Look Like a Trailer

Jun 10, 2024

But to meet the zoning rules, it is designed to be a "caravan" or mobile home.

Richard Chivers via Bowerbird

Seen from afar, English zoning regulations can seem somewhat eccentric. The property that Chestnut Farm is parked on is not zoned to permit a house but did have existing planning rights for two "caravans," defined as "a structure that is designed for human residence and can be transported by road," much like trailer or mobile homes in North America. Remarkably, there is a Caravan Sites Act 1968, which was actually written to protect people who lived in caravans from being evicted by greedy developers, something that happens every day in North America.

Richard Chivers via Bowerbird

What is so wonderful about how PAD Studio designed these caravans is that it is a good model for building lots of houses, whether they have to be caravans or trailers or not.

Richard Chivers via Bowerbird

Let's start at the bottom. The house sits on helical piles—my favorite foundation. No concrete is necessary: The piles are screwed into the ground and when the house has to be moved or is at the end of its useful life, they can be unscrewed, leaving no trace. When I spec'd out my dream house, it was on helical piles. No worries about radon or moisture, and easy detailing; you can build a floor the same way you build a wall or ceiling.

Richard Chivers via Bowerbird

Richard Chivers via Bowerbird

Above grade, the house is built of Structural Insulated Panels (SIPs), a sandwich of foam and wood panel, usually Oriented Strand Board (OSB). The architect tells Treehugger these SIPS are "a combination of locally sourced timber frame and sheathing board with a high insulated rigid board." They wrote earlier that "a SIPs construction method was chosen for its speed of assembly, the airtight quality of the build and because it could be assembled off-site."

Richard Chivers via Bowerbird

Pad Studio

The plan seemed a bit eccentric at first, with the two separate modules connected by a glass walkway when normally these might be mashed together into a "double-wide." But there is a real logic behind this:

Richard Chivers via Bowerbird

The levels of insulation, airtightness, and type of ventilation are all Passivhaus-ish, but PAD Studio tells Treehugger: "We never use the term as whilst we adhere to the principles and push the regulations to the best achievable our clients did not want to do the full testing and certification which would certify it as a Passivhaus."

This is to their credit. There are so many "Passivhaus inspired" or "it's Passivhaus but we didn't want to spend the money on certification." It's not Passivhaus if it's not certified, so this is the straightforward and honest way to deal with it.

Richard Chivers via Bowerbird

Chestnut Farm hits a particular chord for me personally. Twenty years ago I convinced one of Canada's biggest modular builders to let me hire the most talented architects to design modular homes to high standards of energy efficiency. I believed that offsite construction had a lower environmental impact and delivered better buildings in less time. I even wanted them "built on stilts" or helical piles. I wanted to build lots of Chestnut Farms but turned out to be a better writer than I was a prefab salesman, so here I am today.

Richard Chivers via Bowerbird

Pad Studio designed Chestnut Farm for a particular situation, where it legally had to meet the criteria for caravans. But it demonstrates all the virtues of offsite construction, with the bonus of being concrete-free and treading lightly on the land. It's the way we should consider building everywhere.