What is a joist?
A joist, in construction, architecture and engineering, can be defined as one of the horizontal supporting members that run from wall to wall, wall to beam, or beam to beam to support a ceiling, roof structure, or sub-floor. An easy way identify them is to go up in your attic and look at your insulation….your joists are what insulation sits between and what your sheetrock is attached to. Joists are typically constructed of wood, steel, or concrete depending on the type of construction (residential or commercial). An actual floor joist is only used on a two story structure and homes that have pier and beam foundations. If you have a one story home or building, you would refer to that particular joist as a ceiling joist or rafter because there is no floor to support, just a ceiling.
If you are considering remodeling your home, I would definitely consult with an Architect, Builder or qualified design professional to determine the proper joist size you will require in order to properly support the structure of your new room addition or home renovation project.”–Danny Garcia, owner of Rhino Design Build in San Antonio, Texas.
Ceiling and floor joists can be 2×4, 2×6, 2×8, 2×10 and 2×12. The longer the span of a floor joist, the thicker it needs to be. I-joists can also be used as a flooring system to help carry the load if you are adding a second story room addition.