Handrail Height, Grip, and Extensions (2010 ADA Standards 505)
34 to 38 in is the part everybody knows -- and it is a range, so a rail can be too HIGH. Three others get missed. The clearance behind the grip is 1-1/2 in, which a wall bracket eats without anyone noticing. The grip is a WINDOW: a circular rail is 1-1/4 to 2 in, so a 2-1/2 in rail is too fat to grip and fails as surely as a thin one. And the extensions are ASYMMETRIC -- the top is a flat 12 in horizontal from the first riser nosing, but the bottom runs AT THE SLOPE for one TREAD DEPTH, so it is a function of the stair and on a 13 in tread the assumed 12 in is short.
Formula and source
height 34 in to 38 in to the top of the gripping surface, measured above walking surfaces, stair nosings, and ramp surfaces. Clearance behind the grip 1-1/2 in minimum. Circular grip 1-1/4 in to 2 in outside diameter; non-circular grip perimeter 4 in to 6-1/4 in AND cross-section dimension 2-1/4 in maximum. Extensions: 12 in horizontal at the top of a stair and at both ends of a ramp; at the bottom of a stair, one TREAD DEPTH of horizontal distance at the slope of the flight.
2010 ADA Standards for Accessible Design, 505.4, 505.5, 505.7.1, 505.7.2, 505.10.1, 505.10.2, and 505.10.3. A US federal standard in the public domain, quoted directly.
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