R507.5

Section R507.5 is titled 'Deck beams' and covers the requirements for deck beam span, plies connection, and cantilevers. A cross-reference to a figure and table which list allowable spans of wood deck beams based on several variables, multiple ply wood beam connection details, allowable length of wood beam cantilevers, and allowance for other types of beam materials is established. The purpose of this section is to prevent structural failure. Table R507.5 provides allowable beam spans based on joists bearing on the beam from one side only, in accordance with footnote b. Where a beam has joists bearing from spans on both sides, the joist span column used must be adjusted accordingly. Figure R507.5 shows that beam spans are to be taken from the center of the post support (which is different than floor joists which measure their spans from face to face of supports).

The model shows a wood deck being built with the highlighted 2-ply beams each being loaded from only one side (cantilevers are highlighted in a separate color). Notice the fasteners connecting the plies of the beams.