How a cut stair stringer is laid out — framing-square steps, throat depth, and why it shears

Lay out a cut stringer with a framing square (rise on one leg, run on the other), keep the throat ≥ 5″ so it can’t shear at the notch corner, plumb-cut the top to the header, and drop the bottom riser by one tread thickness so all risers stay equal.

A 2-by-12 cut (notched) stair stringer drawn at the stair angle. A framing square lays out each step, with the riser height marked on one leg and the tread run on the other. The throat — the wood remaining behind each notch, measured perpendicular to the bottom edge — must stay at least 5 inches, because a cut stringer fails in shear at the inside corner of a notch (the stress riser) before it ever reaches its bending limit. The top of the stringer is a plumb cut bearing against the header, and the bottom riser is dropped by one tread thickness so every finished riser ends up equal. A cut stringer spans about 6 feet of run (SPF) before it needs support. — Source: AWC DCA 6 (cut-stringer span + 5″ throat); 2021 IRC R311.7

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A 2-by-12 cut (notched) stair stringer drawn at the stair angle. A framing square lays out each step, with the riser height marked on one leg and the tread run on the other. The throat — the wood remaining behind each notch, measured perpendicular to the bottom edge — must stay at least 5 inches, because a cut stringer fails in shear at the inside corner of a notch (the stress riser) before it ever reaches its bending limit. The top of the stringer is a plumb cut bearing against the header, and the bottom riser is dropped by one tread thickness so every finished riser ends up equal. A cut stringer spans about 6 feet of run (SPF) before it needs support.

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    <img src="https://remodelcalculators.com/api/figure-embed/stair-stringer-layout" alt="A 2-by-12 cut (notched) stair stringer drawn at the stair angle. A framing square lays out each step, with the riser height marked on one leg and the tread run on the other. The throat — the wood remaining behind each notch, measured perpendicular to the bottom edge — must stay at least 5 inches, because a cut stringer fails in shear at the inside corner of a notch (the stress riser) before it ever reaches its bending limit. The top of the stringer is a plumb cut bearing against the header, and the bottom riser is dropped by one tread thickness so every finished riser ends up equal. A cut stringer spans about 6 feet of run (SPF) before it needs support." width="800" height="480" style="width:100%;height:auto;border:0" loading="lazy">
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    Diagram: <a href="https://remodelcalculators.com/construction-diagrams/stair-stringer-layout" target="_blank" rel="noopener">How a cut stair stringer is laid out — framing-square steps, throat depth, and why it shears</a> — courtesy of <a href="https://remodelcalculators.com" target="_blank" rel="noopener">RemodelCalculators.com</a>
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Code-compliant stair geometry, stringers & materials per 2021 IRC R311.7 / 2024 R318.7. Straight, L, U, winder, spiral & curved. AWC DCA 6 stringer spans. Free.

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