2x12 Stair Tread Span
The minimum recommended size for a deck stair stringer is 2x12 which has a maximum recommended unsupported span of 6 feet.
2x12 stair tread span. 311 7 4 2 minimum tread depth is 10 max. This configuration results in an effective throat depth of approximately 5 inches for a horizontal span of 12 feet and 3 inches. Timberstrand lsl stair stringers and sturdistep stair treads specifier s guide 9010 ember 2015sept 3 1 1 3e timberstrand lsl sairt stringers maximum stringer run 100 psf live load 12 psf dead load simple span stringer run without intermediate support. Width difference is 3 8 based on all treads 311 7 4 3 stair tread nosing must extend out to a maximum of 1 past front of riser unless the tread is 11 or larger just like above 3 8 max.
I mount stair stringers directly to 2x12 rim joists or to a header set directly beneath 2x8 or 2x10 rim joists. Consider 15 risers at 7 inch tall with 10 inch wide treads and stringers cut from spf no. Only a 2x12 rim joist has enough depth to fasten the stringer hardware to it and provide enough height for the last riser figure 12. 3 steps steel stair stringer black 7 1 2 in.
Often this maximum span is dangerously exceeded resulting in overspanned stringers that will deflect and cause the connection at the deck to pull loose and fail. Discrepancy is allowed the reason for the codes. Composite anti slip stair tread 48 in. Includes 1 stair riser price.
The rim joist must be able to support the additional load of the stairs. The calculator will provide you with the number of stairs riser height and tread depth to cut your stringers. Composite anti slip stair tread 48 in.