A long piece of wood or steel supporting part of the structure of a building, typically arranged in parallel series to support a floor or ceiling.
In the picture below, you can see the joists running vertically between each row of pink insulation. The beams are the much larger wood pieces running horizontally, supported by the pillars.
There are 4 main types of joists that you will run across when working in crawlspaces. They are floor joists, ceiling joists and rim joists.
Floor joists are the boards that are used to frame the floor of a structure. The picture above shows floor joists.
Ceiling joists are boards that frame the ceiling of a structure. They are used to attach rafters and other supports to create the roof framing.
Ceiling joists which are supporting rafters and are connected to the walls below:
Ceiling joists in an unfinished attic:
Rim joists are the first and last joists at the ends of a row of joists that make up floor framing. They go around the 4 edges of the framing where the other joists are secured.
