The 2010 ADA Standards and ICC A117.1 – Accessible and Usable Buildings and Facilities contain similar requirements regarding changes in level within an accessible route. When thresholds are provided in a door opening, the maximum allowable threshold height is 1/2 inch, with the exception of existing or altered thresholds which are permitted to be 3/4-inch maximum in height (refer to the standards for additional criteria).* These limitations on threshold height apply to manually-operated doors and automatic doors.
In addition to the maximum allowable height, the accessibility standards establish the maximum slope for changes in level. A change in level of up to 1/4-inch is allowed to be vertical:
A change in level of 1/4 inch to 1/2 inch must be beveled with a slope not greater than 1:2:
For changes in level greater than 1/2-inch, a ramp with a slope no greater than 1:12 must be used (with exceptions for some existing locations – see below):
In existing buildings where space is an issue, the accessibility standards allow a steeper slope for ramps. If the rise is 3 inches or less, the slope shall not be steeper than 1:8. When the rise is 6 inches or less, the slope may be a maximum of 1:10. A ramp with a slope greater than 1:8 is not allowed.
Although the accessibility standards require walking surfaces to be slip-resistant, the standards do not include prescriptive requirements to establish whether thresholds and ramps used in doorways are required to be treated for slip-resistance. Most thresholds and ramps are grooved to provide some level of slip-resistance, and many manufacturers have optional finishes which create even more friction. These treatments may be helpful for particularly wide thresholds or ramps, or those that would otherwise be smooth and could pose a hazard to building occupants.
The accessibility standards include additional requirements for ramps and sloped walkways, beyond what is addressed here with regard to changes of level within a doorway. The US Access Board publishes an online guide which explains the requirements of the 2010 ADA standards. Chapter 3 is titled Floor and Ground Surfaces, and covers surface characteristics, flooring, openings, and changes in level. Chapter 4 addresses Accessible Routes, including a section on Entrances, Doors, and Gates which contains the requirements for thresholds. The online guide can be accessed here, and the complete requirements can be found in the ADA standards (downloadable here).
* In order to be considered an existing threshold, the installation would have to pre-date the adoption of a code or standard which limited the threshold to 1/2 inch.
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The topic of ADA threshold compliance is an interesting one. We recently had an issue come up in which a consultant refused to accept that the thresholds supplied for the job were ADA compliant, and because the consultant wouldn’t sign off on it, the general contractor was refusing to pay the subcontractor who had provided the frames and thresholds.
The reason this is an issue is that there is a gray area in the standards about vertical rises that show up somewhere other than the edge of the sill. The consultant in this case was insisting that the sill was not compliant because it used two vertical rises (one of 1/4″, one of slightly less than 1/4″) to reach its maximum height instead of a single vertical rise followed by a 1:2 slope. Although my reading of the standards would say that this is a perfectly acceptable way of doing things, it is not explicitly called out as permissible, and the consultant was insisting that it wasn’t. The standards also fail to explicitly call it out as forbidden, and the online guide you reference is also somewhat ambiguous as to whether or not multiple vertical rises are permitted.
I wound up talking to someone at the US Access Board, and was told that the only way to have the ambiguity addressed in a binding fashion would be to find a state or local government building which has a threshold that utilizes multiple vertical rises in an opening that is required to be ADA compliant…and then file a lawsuit that states that it ISN’T compliant. This would force the DOJ (which enforces the standards) to render a ruling on whether or not such sills are compliant with the standard, a ruling that nobody really wants to make without being forced to do so.
All three of the sill manufacturers that I looked at (Endura, Columbia, and AFCO) offer one or more sill lines with this type of profile (including almost all of the Endura ADA line), so I know there have to be hundreds of thousands, probably even millions of them out in the field, but this is the first time I’ve heard of this being an issue. All that to say that the standards have a bit of ambiguity about them on this particular point, so if supplying sills for a job that is being inspected by a consultant for ADA compliance, it might be worth doing some research about the consultant in question.
Thanks for sharing your insight, Tim! An alternative to filing a lawsuit would be to see what the International Code Council has to say about multiple vertical rises. While it doesn’t officially impact the ADA requirements, the two standards are almost the same so it would give us some precedent to help establish the intent of the standards. I’ll put it on my to-do list.