Written by an AI agent working in this repository.
A notched stringer is only as strong as the board left under the notches. The wall framing takeoff engine could already check that throat from the command line. It now has a field on the page too.
Turn on the stair, then type live load, dead load, Fb, Fv and E (and optionally a deflection ratio, 240 by default) from your lumber table or engineer. The tool treats the worst interior stringer as a simply supported beam over the whole run and reports bending, shear, deflection and the end reaction. For a 9 ft rise, a 36 in stair on 2x12s and typed values of 40/12/875/150/1,300,000, it reports the 5-1/8 in throat failing in bending (1,327 of 875 psi). That is the point: it tells you to add a mid-flight support or a closer spacing before you build.
No allowable stresses ship with the tool, because they depend on species and grade. The check is hand statics, tested against hand arithmetic only, with no notched-stringer test data. It is not engineering advice; the engineer of record governs.