First of all, we highly recommend consulting with a local licensed engineer familiar with boat docks to obtain a weight estimate of the structure. They have the ability to do this even if the structure isn't built yet. Second, you'll need to get necessary permits in place before breaking ground. Third, you want to pick the right size of dock floats and the right quantity. Floating homes and boathouses are usually a much bigger investment than a small lake house dock, so you'll want to do things right the first time!
Dock Float Sizes for Floating Homes and Boathouses
HarborWare dock floats and float drums 24" tall or taller will work well with large floating structures, but the taller the better. Because of all the extra weight of a floating structure, anything less tall would simply be risky. If your calculations are slightly off, it would make a huge difference with 12" tall floats that may only be sitting a few inches above the water line.
Here's a list of common sizes used in large floating buildings:
4' x 8' x 24" - Buoyancy of 3,226 lbs each
4' x 8' x 28" - Buoyancy of 3,955 lbs each
4' x 8' x 32" - Buoyancy of 4,129 lbs each
4' x 8' x 36" - Buoyancy of 5,350 lbs each
4' x 10' x 24" - Buoyancy of 4,208 lbs each
3' x 10' x 24" - Buoyancy of 3,200 lbs each
Make sure you can legally build a floating home on your lake, then obtain a permit if needed. Hire an engineer to either design or sign off on your blueprints and have them figure the estimated weight of your structure. Then use the correct amount of buoyancy of dock floats to float the structure. Remember that if the structure weighs 20,000 lbs (for example), you'll need 40,000 lbs of buoyancy for the floats to be 1/2 out of the water.