Deck Joist Span — 24 Inch On Center
Twenty-four inches on center is the widest spacing in DCA 6 Table 2. Spans drop quickly—and many modern decking products do not allow it at all.
All species at 24″ o.c.
Why 24″ is uncommon on finished decks
Table 2 still publishes 24″ values for sawn lumber joists. Southern Pine 2x8 falls to 9'-8" span; Redwood-group 2x8 falls to 8'-8". That can work for short platforms with thick wood decking rated for 24″, but most composite/PVC warranties cap joist spacing at 16″ (sometimes 12″ on diagonal or commercial). Never pick 24″ from the joist table alone—read the decking span rating first (decking vs joist span).
If you already framed at 24″ and need more span, options inside Table 2 are: step up a joist size, switch to a stronger species group, or add a beam to shorten the clear span. The deck joist span calculator reads the same JSON cells.
Related spacing pages: 12″ o.c., 16″ o.c.. Size deep-dives such as 2x10 deck joist span show all three columns side by side.
FAQ
Can I use 24″ o.c. under composite boards?
Only if the board manufacturer explicitly rates that spacing for your orientation and load. Many do not. The joist table cannot override a product warranty.
Does wider spacing increase overhang?
Sometimes the tabulated LO rises when main span falls—still limited by L/4. See overhang rules.