Built on Stilts: A Small House Built With Concrete-Free Foundations

There other ways to build without sitting on a concrete iceberg.

Cabin Cantilevered

Matias Bervejillo

The "concrete iceberg" in homes is made up of the footings and foundations that are usually hidden beneath the surface. But as a recent study showed, it can represent 35% of the upfront carbon in a building. It's one of the reasons we show so many structures that we say are built on stilts; it uses much less concrete. This new cabin under construction is built on steel stilts and uses no concrete at all.

Leah Martin is the founding principal of Seattle architecture firm Allied 8, which works "from the belief that great design is engaging, more inclusive, less wasteful, beautiful and creates a place where people thrive." The firm designed Orcas House for her intergenerational family.

"Determining the site of the home was the first step; the goal was to remove no healthy trees and find the views through the forest. However, finding a site to build on such a lot is a challenge. There’s hardly enough level surface to create a foundation platform, plus the terroir is primarily moss and solid bedrock. Leah’s solution to this was to indeed not create a foundation; instead, the Orcas House connects to the earth in only six locations, sitting upon a steel moment frame instead. This allows the house to gently hover above the site, and cantilever over one end."
steel frame cantilevering out over hill
steel frame cantilevering out over hill.

Allied 8

The firm said concrete is responsible for 8% of global carbon emissions, which is on its own a good reason not to use it, but there are many other good reasons to build on stilts. It noted, "The preciousness of the land and the surrounding forest informed the shape of the house and the surgical foundation system–among the mature trees, using concrete in this home made little sense to the designers."

Wood I-Joists installed between steel beams
Wood I-Joists installed between steel beams.

Allied 8

There is a bit of déjà vu happening for me while reading this because I did the same thing for my family cabin for the same reasons. My terroir is the solid rock of the Canadian Shield, on a site with many beautiful trees that I wanted to preserve, so a long, thin cabin is inserted between them, on wooden stilts sitting on round concrete piers.

steel frame being installed


The steel moment frame is a more elegant solution, avoiding all the built-up wood beams and diagonal bracing that I had to install to hold it up. It has fewer posts, and is probably lighter. They are also able to avoid even the little bit of concrete I had poured into sonotubes because the steel can be used below grade; it is stronger because it is continuous.

We complain often that steel also has significant upfront carbon emissions and making it from iron ore is responsible for greater global carbon emissions than concrete, but Martin ensured they used 100% recycled U.S.-made steel. Surprisingly, they noted, "the alternative construction added only about 10% to the foundation cost." I would have thought it would actually cost less, as it is so minimal.

view toward end

Matias Bervejillo

If I have one criticism of this cabin, it is the kitchen design with that long run along one wall right in the living area. I can never understand how one can have a multigenerational home where you can't put up some kind of baby gate to keep children and dogs out of the cooking area. I put ours at the end. But then, I have been griping about this kind of kitchen forever.

looking back from end


Other than that, it is a lovely interior and the way the lofts were constructed down the middle where it is high enough to stand makes it an interesting ceiling.

Looking at kitchen from living


The most admirable feature of this cabin is the restraint, and the treading lightly on the land.

The firm stated: "There was a commitment to keep the home small in order to keep the forest intact but there were practicalities like storage, mechanical rooms, and extra sleep space for kids and friends so a loft space was designed in the trusses to accommodate these uses. Every window is operable, and the forest aroma fills the site in the summer as the douglas firs warm up–allowing ventilation and site-specific freshness into the home."

Section showing structure
Interesting section showing structure.


It seems these days that all the little cabins are getting knocked down for monster second homes with air conditioning systems. It's a pleasure to see a 1,300-square-foot one with lofts in the rafters and stilts under the floors, where you can actually enjoy the smell as well as the view.

Allied8 also did a church conversion that we admired.

View Article Sources
  1. "Decarbonization challenge for steel." McKinsey and Company.