Dimensional Tolerances in Construction and for Surface Accessibility

1.1.17 Stairs. Measure cast - in - place stairs for both riser height and tread depth of each riser and tread. For stairs 60 in. (1520 mm) or less in width, measure along a line approximately 18 in. (460 mm) from the wall or outside edge of the stair. For stairs with intermediate handrails take additional measurements approximately 15 in. (380 mm) on both sides of the intermediate handrail.

Measuring about 18 inches from the wall or edge of the stair places the measurement about where foot traffic is most likely.

Measure stair riser height as the vertical dimension between tread nosings. If a tread slopes for drainage, use a level or digital inclinometer to extend the line of the upper nosing to allow measurement to the nosing below.

This is consistent with the Life Safety Code method of measurement and reflects the position on a tread that a person's foot is most likely to contact, especially going down a stair. However, requiring the use of a level makes measurement more difficult and/or time consuming. If treads sloped uniformly for drainage, measurement could be made at the riser, from nosing to tread below because the measurement would be the same as using a level to measure from the back of the tread.

For exterior stairs sloped from the riser to the nosing for drainage, measure the slope of each tread using a digital inclinometer placed along a line as indicated in 1.1.17.