Joist Span

The unsupported horizontal distance a floor or ceiling joist must bridge between supports. Maximum allowable span depends on joist species, grade, size, spacing, and load requirements.

Exceeding the allowable span causes bouncy, unsafe floors, so building codes publish span tables that pair each joist size and spacing with a maximum distance. Tighter spacing, deeper joists, and stronger species all extend how far a joist can safely reach.