How to Build a Floating Home

How to Build a Floating Home

By Allie Weiss / Published by Dwell — May 12, 2015

We spoke with architect Eric Cobb about the process behind building a floating home. For his first floating house project, an elegant dwelling in Seattle built by G. Little Construction, Cobb extensively researched methods of retaining buoyancy. Here, in his own words, he shares his insights and the fundamental differences between building houses on land and houses on water.

The older floating homes are built on giant logs that float. These are the ones that are sagging; over time the buoyancy of the logs is reduced. Divers keep having to go underneath them to place pressure-filled barrels to lift the home.

Architect Eric Cobb was hired to design an 1,800-square-foot floating home for a Seattle couple. It was prefabricated at a shipyard in Port Townsend, Washington, and traveled by tugboat to its final destination, Seattle’s Lake Union.

In the types of floating homes that are built right now, there are [two building options]. All floating homes now are built with concrete floats. In one, the concrete works as a giant floatation device with Styrofoam inside it, where the Styrofoam is floating and the concrete is forming an upside-down bowl over the Styrofoam. The Styrofoam does lose some of its buoyancy over time, and then the only recourse is to put barrels underneath. The other option is that the concrete float ends up floating because it’s displacing water. It’s a bowl filled with a void. This decision impacts how you’re going to build it and the whole process after that. 

The exterior of a floating house in Seattle is clad with fiber cement panels from James Hardie painted in three slightly different hues: Fiery Opal, Navajo Red, and Rich Chestnut by Benjamin Moore.

In the latter scenario, you have to keep water out of the float or it will sink. Unlike a house, where you’re on dry land and you might have damp soil that’s trying to work its way through your concrete foundation, here you have massive amounts of water pressure looking for any crack to power water into your displaced cavity. You have to use water-proofing measues [to prevent this].

Floor-to-ceiling windows in the main living space overlook Lake Union.

You have to watch your weight on water. Add a couple thousand pounds here and it goes down half an inch. The flip side is that a few barrels take care of that. Barrels do move and sometimes they pop out. There’s a bit of ongoing float adjustment for all floating homes.

There’s a fundamental difference between whether the home is built on land or built in water. Building in the water is much more popular, but you can’t use a plumb bob or level because it’s moving all the time. It’s a real challenge to build a house when you can’t use any of the tools we [typically] use for building. If you build on land, however, you have to use gigantic travel mechanisms to transport it. You’re dropping it in the water and keeping your fingers crossed that it’s going to work out like you want. 

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