Notched stair stringer
Notched stair stringer
(OP)
I am checking the stringer capacity for an existing stair. The stringer is a Trus Joist 1.3E LSL 2x12 (1 1/2"x11 1/4"). The stringer has been notched for steps (7 3/4" rise, 10" run). There are 12 steps which makes the total run 120" and the total rise 93". The pair of stringer are 36" apart. I am using 10psf dead load and the required 40psf live load. This stringer does not work. Is there something that I am missing?





RE: Notched stair stringer
With wood contruction I use stinger spacing of 18" or 24" OC (reduces the tread deflection and stringer stress). Loading I use for stair systems is 100 psf. Dont forget about the hand rail loads and resisting its rotation. Consider nailing and gluing the treads and risers.
RE: Notched stair stringer
RE: Notched stair stringer
RE: Notched stair stringer
RE: Notched stair stringer
Is part of the stringer cut flat on the bottom? Maybe you can pick up a few inches here and there to reduce the actual clear span to make it work for moment (assuming that is what is governing)
RE: Notched stair stringer
RE: Notched stair stringer
You said a Truss Joist which is an "I" member with two flanges and a web. When you notched the member you destroyed the flange and ruined the member. The standard stringer is a 2x12 at 18" o/c for a 36" stair.
RE: Notched stair stringer
My quick check indicates that the net effective member (1 1/2" x 5 1/8") spanning 10 feet fails in both bending and deflection using 100 psf. At 40 psf bending works, but it's a little bouncy. I think most codes allowthe use 40 psf for residential stairs that serve one dwelling, but I prefer 100 psf. 100 psf is required for egress stairs on multi-family residences.
Make sure they didn't over-cut the stair notches!
RE: Notched stair stringer
RE: Notched stair stringer
RE: Notched stair stringer
RE: Notched stair stringer
The inside face of the stringer is accessible as is the bottom edge.
RE: Notched stair stringer
RE: Notched stair stringer
Add 2x4 (or 2x6) to the inside face of stringer.
Add 4x4 posts ((2)-2x4's) at two locations at the underside of stringer.