Knee and Toe Clearance (2010 ADA Standards 306)
What makes a lavatory or work surface usable, and what gets built wrong because an open space looks clear.
Example
You enter
- Height of the underside of the element (in) 26
- Knee depth available at 9 in above the floor (in) 17
- Knee depth available at 27 in above the floor (in) 14
- Toe depth available below 9 in (in) 17
- Clear width under the element (in) 30
You get
- Apron shortfall (in) 1
- Taper allowed (in) 3
- Toe clearance 0
- Width 0
- Required knee depth at 27 (in) 8
Details, formula, and sources
Two stacked zones: TOE from the floor to 9 in, KNEE from 9 to 27 in, both 30 in wide and neither more than 25 in deep. Knee depth is not one number -- 11 in at 9 in above the floor and 8 in at 27 in, tapering no faster than 1 in of depth per 6 in of height, which is exactly what a slanted apron or a hanging bowl violates. And the 27 in figure decides the job: an apron at 26 in has NO knee clearance at all, not shallow clearance, and no depth below can rescue it.
toe clearance = the space from the floor to 9 in, 17 in deep minimum where required and 25 in maximum, 30 in wide minimum. Knee clearance = the space from 9 in to 27 in, 11 in deep minimum at 9 in and 8 in deep minimum at 27 in, permitted to reduce between them at 1 in of depth per 6 in of height, 25 in maximum and 30 in wide minimum. An underside below 27 in provides no knee clearance.
2010 ADA Standards for Accessible Design, 306.2.1 through 306.2.5 and 306.3.1 through 306.3.5. A US federal standard in the public domain, quoted directly.
The 2010 ADA Standards are published in full at no cost at ada.gov and by the US Access Board.
Estimate. AHJ and licensed professional govern.
Field names used by the API: apron_height_in, knee_depth_at_9_in, knee_depth_at_27_in, toe_depth_in, clear_width_in, apron_shortfall_in, taper_allowed_in, toe_deficit_in, width_deficit_in, required_knee_depth_at_27_in
- Toe zone floor to 9 in; 17 in deep minimum where required, 25 in maximum2010 ADA Standards 306.2.1 to 306.2.3
- Knee zone 9 in to 27 in above the finish floor2010 ADA Standards 306.3.1
- Knee depth 11 in minimum at 9 in, 8 in minimum at 27 in2010 ADA Standards 306.3.3
- Taper rate 1 in of depth per 6 in of height, no faster2010 ADA Standards 306.3.4
- Width 30 in minimum for both zones2010 ADA Standards 306.2.5 and 306.3.5
- Maximum depth 25 in under the element, both zones2010 ADA Standards 306.2.2 and 306.3.2