Floor Structure

There are two main types of floors: raised floors that are wood framed, and floors built on concrete slabs.

Beneath a raised, finished floor there is generally a sub floor, supported by joists and beams, posts, and, in a two-story house, bearing walls. Joists may have solid or diagonal bridging between them to provide extra strength. A slab is just a flat, thick surface of concrete poured on the ground.

If you are installing new flooring or making repairs to existing floors, you may need to know what kind of sub floor you have. A raised sub floor is typically constructed from 1-by-4 or 1-by-6 lumber or 4-by-8-foot plywood panels. With a lumber sub floor, boards are laid diagonally across joists. A plywood sub floor's panels are nailed to the joists, laid with the ends butted together. On a concrete slab, a plywood sub floor is typically laid over wood 2-by-4 sleepers that are fastened to the slab.