Deck Joist Cantilever Rules and Limits

The distance your joists can safely cantilever or overhang a drop beam is determined by the size of the joists, the wood type and grade of the lumber and the spacing between joists. Many building departments limit joist cantilevers to 24" maximum. Generally, you should use at least five framing nails to attach the rim joist to the ends of your joists. It's highly recommended to always contact your local code department to ensure all code and safety requirements are being met before building any decking structure.

The American Wood Council states that cantilevers are limited to 1/4 the span of the joists. 

 Joist Spacing (o.c.)    12" 16" 24" 
 Species  Size  Allowable Overhang
 Southern Pine  2x6 1'-0" 1'-1" 1'-4"
 2x8 1'-10"  2'-0"  2'-4"
 2x10  3'-1" 3'-5" 2'-10"
 2x12 4'-6" 4'-2" 3'-4"

 Douglas Fir-Larch,

Hem-Fir,

Spruce-Pine-Fir

 2x6 11" 1'-0" 1'-2"
2x8  1'-8" 1'-10" 2'-2"
2x10  2'-10" 3'-2" 2'-9"
2x12  4'-4" 3'-11"  3'-3"

 Redwood,

Western Cedars,

Poderosa Pine, Red Pine

 2x6 9" 10" 11"
2x8  1'-5"  1'-7" 1'-9"
 2x10 2'-5" 2'-7" 2'-8"
 2x12 3'-7"  3'-9" 3'-1"
 
Maximum allowable overhang cannot exceed 1/4 of the actual main span.