Threshold Height Limits on an Accessible Route

Door thresholds help manage weather, but they can create a barrier if too high or abrupt. Accessibility standards limit the height and shape of changes in level along an accessible route.

The 1/2-inch threshold limit

Section 404.2.5 of the 2010 ADA Standards generally limits thresholds at doorways on accessible routes to 1/2 inch. The provision allows a vertical change up to 1/4 inch; a change greater than 1/4 inch and up to 1/2 inch must be beveled at no steeper than 1:2. The Standards include a limited exception for existing or altered thresholds up to 3/4 inch high with a bevel on each side no steeper than 1:2; do not apply it automatically to new construction.

Check the complete route

Threshold compliance is one part of an accessible doorway. Clear opening width, maneuvering clearance, door hardware, opening force and the adjoining floor surfaces also matter. A compliant threshold does not make an otherwise inaccessible entrance compliant.

Coordinate weather and access details

• Select a threshold profile that meets height and bevel limits.
• Coordinate sill pan, flashing and exterior drainage without raising the finished transition excessively.
• Measure after flooring and exterior paving are installed, not only at rough framing.
• Check local accessibility and building-code requirements, which may be stricter or apply to different facilities.
• Provide an accessible route to the entrance and through the doorway.

Field sequence: measure, classify, coordinate

Measure the finished transition at the doorway, including the highest point created by the threshold, flooring, sealant, or an adjacent ramp. Record the vertical change rather than relying on a product cut sheet. Under the 2010 ADA Standards, a change up to 1/4 inch may be vertical; a change over 1/4 inch and up to 1/2 inch must be beveled no steeper than 1:2. The ordinary maximum threshold height is 1/2 inch. The Standards also contain an exception for existing or altered thresholds up to 3/4 inch high with a bevel on each side no steeper than 1:2; do not apply that exception automatically to new construction.

Check whether the doorway is part of an accessible route, then compare the work with the applicable adopted building code, project documents, and governing accessibility standard. The ADA Standards set a federal accessibility baseline; state or local code may add requirements. Confirm that the threshold detail works with the door sweep, sill pan, flashing, and drainage plane. A weather-resistant detail still needs a compliant transition and a surface that remains stable and slip resistant.

Consider a retrofit where new tile raises one side of an existing opening. A nominal half-inch threshold can exceed the limit once the tile, mortar, and transition profile are installed. The installer should coordinate finished elevations before setting the frame, then remeasure the completed assembly. If the existing-condition exception may apply, document why the opening qualifies and check both bevels instead of assuming the exception follows the building automatically.

Check the full route on both sides: a compliant threshold does not cure a steep approach, abrupt flooring lip, door maneuvering obstruction, or poor drainage that leaves standing water. Inspect the accessible path in its completed condition, with permanent floor finishes installed and the door operating. Photograph the measurement with a ruler or level, note the measurement point, and resolve a failed condition before turnover rather than hiding it with a loose ramp.

Common errors include measuring the exposed metal alone, overlooking a floor finish installed later, confusing the general 1/2-inch cap with the existing-or-altered exception, and treating a beveled edge as permission for any height. Check each doorway in sequence and record the governing detail. If field conditions force a change, obtain approval from the design professional and accessibility reviewer before altering the sill or frame.

Exceptions and coordination details

A threshold detail should show both the nominal product height and the finished transition after flooring, sealant, and any sill pan are installed. For changes in level, distinguish the doorway threshold rule in §404.2.5 from the general surface-change provisions in §303. The existing-or-altered threshold exception has specific conditions and does not turn a new high threshold into an acceptable design. If a project is an alteration, document the existing condition and consult the design professional about the exception and any readily achievable or technical-infeasibility provisions that may separately matter.

Coordinate the accessible route continuously through the opening. Check the approach and landing slopes, maneuvering clearance, door opening force and hardware, floor finish, and drainage. If a threshold is beveled, make sure the bevel is stable and integrated rather than a loose wedge that can move under traffic. Where the door is part of an accessible means of egress or automatic door system, check the other relevant standard sections too; one compliant dimension does not establish complete doorway compliance.

For a mock inspection, have one person measure while another records the section, finished-floor reference, threshold peak, and both approach elevations. Repeat the reading at any variation along the opening. A bowed sill or uneven tile can make the center compliant while one end exceeds the limit. If measurement is disputed, use a level and straightedge to identify vertical change, photograph the setup, and ask the accessibility reviewer to confirm the interpretation before closeout.

When the planned product cannot meet the required height and water detail at once, elevate the coordination issue early. The architect, door supplier, waterproofing contractor, and accessibility consultant can select an integrated sill/pan assembly. Late field grinding can break a thermal barrier, remove a listed component, compromise the seal, or create an uneven edge. Record the approved detail revision and inspect the completed opening after all floor trades finish.

Exam takeaway

For the 2010 ADA Standards, remember the 1/2-inch maximum and the 1:2 bevel for changes above 1/4 inch. Verify the full doorway and route, not just the threshold.