Stair headroom and the three clear widths

Headroom is measured vertically from the sloped line adjoining the tread nosings, so it is an envelope parallel to the stair, not a single measurement. Clear width is three different numbers depending on how many handrails are installed.

Left, a stair section showing the sloped line joining the tread nosings, with a shaded 6 foot 8 inch clearance envelope drawn parallel to it and dimensioned at both the bottom and top of the flight to show the clearance is constant along the stair rather than measured at one point. Right, three stair sections showing clear width: 36 inches above handrail height with no rails, 31 and a half inches at or below one handrail, and 27 inches with handrails on both sides. — Source: 2021 IRC R311.7.1, R311.7.2 (2024 IRC R318.7.1, R318.7.2)

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Left, a stair section showing the sloped line joining the tread nosings, with a shaded 6 foot 8 inch clearance envelope drawn parallel to it and dimensioned at both the bottom and top of the flight to show the clearance is constant along the stair rather than measured at one point. Right, three stair sections showing clear width: 36 inches above handrail height with no rails, 31 and a half inches at or below one handrail, and 27 inches with handrails on both sides.

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    <img src="https://remodelcalculators.com/api/figure-embed/stair-headroom-width" alt="Left, a stair section showing the sloped line joining the tread nosings, with a shaded 6 foot 8 inch clearance envelope drawn parallel to it and dimensioned at both the bottom and top of the flight to show the clearance is constant along the stair rather than measured at one point. Right, three stair sections showing clear width: 36 inches above handrail height with no rails, 31 and a half inches at or below one handrail, and 27 inches with handrails on both sides." width="800" height="540" style="width:100%;height:auto;border:0" loading="lazy">
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    Diagram: <a href="https://remodelcalculators.com/construction-diagrams/stair-headroom-width" target="_blank" rel="noopener">Stair headroom and the three clear widths</a> — courtesy of <a href="https://remodelcalculators.com" target="_blank" rel="noopener">RemodelCalculators.com</a>
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