What headroom is expected over a residential stairway?

Stair headroom is measured from a sloping plane connecting the tread nosings up to the surface above, which is the geometry a person's head actually follows while climbing. Measuring to the ceiling from the floor would give a misleading figure, because on a stair the user rises as they advance, so the clearance that matters is perpendicular to their path rather than vertical from any one point. The commonly applied minimum for residential stairs is six feet eight inches. Inadequate headroom appears most often at basement stairs beneath a landing, a duct or a beam, and it is genuinely hazardous — a strike to the head on a stairway happens while the person is in motion on an unstable surface, so the secondary fall is often worse than the impact.

Residential stair headroom is measured from a plane connecting the tread nosings to the surface above, with six feet eight inches the commonly applied minimum. Measuring from the nosings reflects the path a climber's head actually takes.

Stairway headroom is measured vertically from the sloped plane through the tread nosings to the lowest projection above, with a commonly applied residential minimum of six feet eight inches. Obstructions such as beams, ducts and landings above are frequent causes of deficiency.

Measure From the Nosings, along the slope the climber follows. Floor-to-ceiling is a room measurement, not a stair one.

Look for the obstruction rather than the average. Headroom is usually adequate over most of a flight and deficient at one beam or duct.

• •Measuring vertically from the floor rather than from the nosing plane
• •Confusing habitable room ceiling height with stair headroom
• •Averaging across the flight rather than measuring at the obstruction