Thresholds and Changes in Level

Why this matters

The edge that stops a wheelchair or catches a shuffling foot is usually not a step. It is a half inch of oak saddle at the bathroom door, a carpet strip that rose when the pad compressed, or a new plank floor laid over the old one that left every doorway with a lip. Each one is small enough that nobody in the house notices it until the person who uses a walker trips on it at 2 a.m. These are the cheapest fixes in an accessibility job and the ones most often skipped, because the scope was written around the bathroom and the hallway was never measured.

The numbers, and what they are

The 2010 ADA Standards for Accessible Design do not govern a private single-family home. They are still the best dimensional reference available, because they were built from research on how wheels and feet actually behave at an edge, and an occupational therapist (OT) will recognize them. Treat them as a reference, not a requirement. See related: What the ADA Does and Does Not Cover in a Private Home, which owns the law layer.

A 1:2 bevel rises one unit for every two units of run. A full 1/2 in change beveled at 1:2 needs at least 1 in of horizontal run. If the bottom 1/4 in is a vertical face, the bevel above it carries the remaining 1/4 in over at least 1/2 in of run.

                    bevel 1:2 or flatter
                 ________________ higher floor
                /
               /   remaining rise over 2x its run
   ___________|    up to 1/4 in vertical face
   lower floor
              |<->| run of the beveled part
   total change 1/2 in max; above that, ramp it

What actually happens at an edge

Knowing the mechanism tells you which number matters for which person.

• A manual chair's front casters are small, often 4 to 6 in across on an everyday chair and smaller on a lightweight one. A small wheel meets a vertical face nearly head-on, so a 3/8 in lip that a 24 in drive wheel would roll over stops a caster dead and pitches the rider forward. Experienced users pop the casters up a wheelie over an edge; many older users cannot, and an attendant pushing from behind cannot either without tipping the chair back.
• A power chair has the mass to climb more, and the user often cannot feel the jolt or brace against it. The risk shifts from getting stuck to a hard stop at speed.
• A walker with front wheels or glides catches on any vertical face, and the person's weight is already forward over it. That is the fall you are trying to prevent.
• A shuffling gait, common with Parkinson's disease and after some strokes, lifts the toe a fraction of an inch. For this person the bevel is not enough by itself. A 1:2 bevel still presents a rising surface the toe can catch; a flush floor or a long, shallow transition is what works.

So 1/2 in beveled is a ceiling for a chair, not a target, and it is the wrong target for a shuffling walker. Aim for flush wherever the floor allows it.

Interior doorways and floor-covering transitions

Interior lips come from three sources, and the fix differs.

A raised saddle or threshold strip at a bathroom or bedroom door, often there only to hide a seam. Remove it and replace it with a flush transition or a low reducer. This is usually an hour of work per door.

Stacked flooring. New plank or tile laid over an existing floor raises one room by the new floor's full thickness. Where the room meets an untouched hallway, the change can run 3/8 to 3/4 in. A reducer molding bevels it, but if the change exceeds 1/2 in, the reference treats it as a ramp, and a reducer that steep is a toe-catcher. The honest fixes are to remove the old floor before laying the new one, or to bring the lower floor up with an underlayment so the two meet. Plan the floor heights before the floor goes down; afterward every fix is a compromise.

Carpet. Thick pile and a soft pad make a chair work much harder, and carpet edges creep up as the pad compresses and the stretch relaxes. The reference uses 1/2 in maximum pile with a firm pad or none, and trim fastened along the entire exposed edge. A carpet-to-hard-floor transition that measures fine at install often measures high a year later, because the pad crushes on the walking line and not at the strip.

Exterior doors: why they are high, and what you can do

Exterior thresholds are high for a reason: water. A threshold is part of the door's weather seal, and a sill that sits flush with the porch invites driven rain under the door. That is why the fix is never simply "lower the threshold."

The residential code adds a second constraint. The 2021 IRC, at R311.3.1 as adopted by your jurisdiction, generally limits the drop from the top of the threshold to the exterior landing at a required egress door to 1.5 in, with an exception allowing up to 7.75 in where the door does not swing over the landing. Many older houses have a single tall step down instead, which no threshold product solves.

The options, roughly in order of how well they work for a chair:

1. Raise the exterior landing to meet the interior floor, sloped away from the door for drainage. This is the real fix and usually means concrete or deck work.
2. A low-profile threshold designed for accessible entries, paired with a sill pan, door sweep and a covered or well-drained landing so the lower sill does not admit water.
3. A threshold ramp, a small wedge on one or both sides. Once the change passes 1/2 in, the reference treats the wedge as a ramp, so the 1:12 slope applies: a 2 in rise wants a wedge 24 in long, not the 4 in to 6 in many off-the-shelf pieces run. See related: Ramp Slope, Rise and Landings.

Shower thresholds follow their own reference, in 608.7. See related: Curbless Showers and Where the Water Goes.

A worked survey: five transitions in one house

A shop is scoping a single-story house for a woman in her late seventies who uses a rollator (a four-wheeled walker with a seat) inside and a transport chair, pushed by her husband, for longer trips. The OT's note says she shuffles when tired. The tech measures every transition on her daily route with a straightedge across the higher floor and a tape at the edge, recording the vertical face and the total change separately.

Reading the table against the person, not just the numbers:

• Hall to bathroom is the priority. It fails the reference on two counts (over 1/2 in, and the whole 5/8 in is a vertical face), it sits on the night route to the toilet, and it is the cheapest fix in the house.
• The kitchen passes the reference: the 1/8 in face is under the 1/4 in allowed, the 7/16 in total is under the 1/2 in ceiling, and the beveled part (7/16 minus 1/8, so 5/16 in) needs at least 5/8 in of run at 1:2. The reducer measured about 3/4 in of run, flatter than 1:2. It passes for her rollator. It is also the change most likely to catch a shuffling toe. Because she shuffles when tired, the tech flags it as the next fix rather than calling it done: a longer, flatter transition piece would cost little.
• The carpet is a 3/8 in vertical face, which fails the 1/4 in no-treatment limit even though the total is under 1/2 in. A beveled trim strip fixes it; so does a re-stretch, because the edge has risen since install.
• The back door is 2 1/2 in total. No threshold product handles that, and a wedge would be roughly a 1:2 slope if squeezed into a few inches. That is the ramp and landing conversation, and it changes the job's scope and probably its permit. It goes on the scope as a separate line.

The summary for the scope: of five transitions, one is clean, three fail or are flagged on the reference, and one is out of a threshold's reach entirely. The two cheapest fixes are the bathroom saddle and the carpet edge, and the saddle sits on her nightly route to the toilet.

What changes the answer

The person's device and gait decide which number governs. The 1/2 in bevel is written around wheels. For a shuffling walker, any rising face is the hazard, and the target becomes flush. For a power chair user with good trunk control, a 1/2 in bevel is routine. Watch them cross it before you decide. See related: The Accessibility Walkthrough With the Person Who Lives There.

A progressive condition moves the target. Someone walking with a cane today may use a rollator next year and a chair after that. Fix to the device they are heading toward when the cost difference is small, which for an interior saddle it almost always is. See related: Designing for a Progressive Condition.

A rental changes who decides. In a rented home, removing a threshold is a modification the landlord may have to permit. See related: Reasonable Modifications for Tenants.

How to verify the work

Measure after the work, not just before. Lay a straightedge across the higher floor so it overhangs the edge, and measure down to the lower floor at three points along the doorway, because floors are rarely flat across a 32 in opening and the worst point is the one that catches. Record the vertical face and total change separately, since the reference treats them differently.

Then have the person cross it with their own device, in both directions, at the pace they actually move, including when tired if that is when they shuffle. A transition that measures 3/8 in and still catches her rollator glide is not fixed. A carpet edge gets re-measured at the first follow-up visit, because it is the transition most likely to have moved.

References

• U.S. Department of Justice, 2010 ADA Standards for Accessible Design, sections 302, 303, 404.2.5 and 608.7 (used here as a dimensional reference, not a requirement for a private home)
• International Residential Code, 2021 edition, R311.3.1 (floor elevation at required egress doors), as adopted by your jurisdiction
• See related: What the ADA Does and Does Not Cover in a Private Home
• See related: Ramp Slope, Rise and Landings
• See related: The Accessibility Walkthrough With the Person Who Lives There