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.
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.
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].
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.
Here, watch a video of the floating home Cobb designed being transported to its final destination on Seattle's Lake Union.