Span Table
CSI Division 06, Wood, Plastics, and Composites
An engineering reference chart that tells a framer what size and species of lumber, or what engineered lumber product, is required to safely span a given distance while carrying a specified load, used to size headers, floor joists, ceiling joists, and roof rafters.
Why it matters
A beam or joist that looks strong enough by eye can still be badly undersized for its actual span and load. Span tables take the guesswork out of framing by translating building code requirements into a simple lookup: given this span and this load, use at least this size member.
On a real project
A carpenter framing a floor checks a span table to confirm that a floor joist spanning twelve feet, under the load the code requires for that room's use, needs at least a specific depth and spacing, rather than relying on whatever lumber size was used on a previous, different job.
Who this matters most to
A Carpenter references span tables constantly while framing, since the correct lumber size changes with every different span, load, and spacing combination.
Where this goes wrong
A framing crew reuses a joist size from a previous project on a new floor with a longer span, without checking a span table for the new dimensions. The floor ends up with noticeable deflection, bouncing underfoot, because the joists were never actually sized for this particular span.