More Joists and Stairway Opening

Hmmm...

Joists are nearly all in place. The process is a bit slower than for a square house--lots of angles! The blue blob in the center is the plywood that will go on next.

Notice the opening for the stairs in the central foreground.

I decided to use 3/4 inch tongue-and-groove plywood for the floor instead of oriented strand board (OSB). Although OSB is becoming the industry favorite (around here almost 100% of homes use it for floor, exterior wall, and roof sheathing), it has its drawbacks: When used on the floor, there is enough give when walked on to crack ceramic tile; It is not good for hardwood flooring; and, although it is sealed at the factory to protect it from the weather and moisture, cut edges loose that seal and will absorb moisture and swell. On this house, there will be a lot of cut edges.

Plywood has its drawbacks, too. It is more expensive, though not as much as I thought--about $300-400 for the entire project. The biggest concern is that it can delaminate when exposed to water for a long time. So, I will need to protect it until I get the house up, especially if I don't get the dome up this fall. The plan is to cover it with something waterproof and to heat the basement, even if the dome isn't up. That will help with the moisture from the top as well as from below,