Deck Joist Span & Cantilever Calculator (IRC R507.6)
Calculate maximum deck joist spans and cantilever overhangs for 2x6, 2x8, 2x10, and 2x12 pressure-treated lumber per IRC Table R507.6 building codes.
Calculated Results
Frequently Asked Questions
What is the maximum allowed span for a 2x8 deck joist?
Under the International Residential Code (IRC Table R507.6), a #2 Southern Pine 2x8 spaced 16 inches on-center can span up to 12 feet 10 inches without cantilever (or 11 feet 10 inches with maximum cantilever).
How far can a deck joist overhang (cantilever) past the support beam?
Under IRC R507.6, the maximum cantilever overhang is strictly limited to one-fourth (1/4) of the actual joist span between supports, but cannot exceed table limits (typically 2 to 3 feet for 2x8/2x10).
Why does composite decking require 12-inch or 16-inch joist spacing?
Composite and PVC decking materials (Trex, TimberTech) have lower structural stiffness than wood. Perpendicular decking requires a maximum of 16" OC, while diagonal 45-degree herringbone decking requires 12" OC to prevent sagging.
What design load does IRC residential deck code require?
Standard residential deck building codes are calculated using a 40 psf (pounds per square foot) live load (occupants, furniture, snow) plus 10 psf dead load (deck materials) with an L/360 deflection criteria.