What is a floor joist?

Floor joists are horizontal supports used to frame open spaces in your home.  

Joists work with the floor structure to strengthen the subfloor shearing, which makes it possible for it to act as a horizontal diaphragm. Typically, the beams are put in place after the crawl space or basement has been constructed.  

In order to hold up the floor above, joists must span between load-bearing walls or beams, which transfer their weight to vertical elements, and they must be parallel and evenly spaced apart.