Go to Mobile Site  Frequently Asked Questions  How are the floor
joist span tables calculated and used?  Floor joist span tables
are tabulated based on allowable deflection limits of L/360.
Floor live loads range from 30 psf for sleeping areas to 40 psf
for other occupancies. Ceiling joist span tables are tabulated
based on allowable deflection limits of L/240.  Typically a user
will know the span and desired spacing for a given application.
The user can select a species, size, and grade for trial use.
Using the Design Values for Joists and Rafters, the user
determines the modulus of elasticity and bending design value of
the species, grade and size of lumber. Bending design values are
already adjusted for load duration and repetitive member factors
in the Design Values Supplement. With this information the user
enters the span table with the given modulus of elasticity and
determines the allowable span for an estimated size and spacing.
If the allowable span is greater than that required for the
application,