Deck Beams and Joists
Deck beams and joists need to be sized, spaced, and supported properly to support the loads that they are subjected to. The tables in 2021 IRC R507.5 list maximum beam spans for the different wood species members based on various ground snow loads. Table R507.6 helps to determine the maximum joist span, considering live load, wood species, joist spacing, joist size, and whether there’s a cantilever or not. Cantilevers are included but are maxed out at L/4. Joist spacing should be no more than 16″ o/c for decking that runs perpendicular to joists and no more than 12″ o.c. if the decking runs diagonal to them. DCA 6, Table 2 is the comparable section that addresses maximum joist spans and overhangs. These member sizes and spans are developed using established code minimum distributed loads of 40 psf live and 10 psf dead.