Transition Profiles and the Accessible Level Change
Why this matters
A transition is the smallest piece on the job and the one people walk across most often. Pick the wrong profile and the floating floor pinned under it buckles, the reducer that fit the samples leaves a sharp lip once the real floor goes down, and on a public job a lip a little over a quarter inch can fail an accessibility inspection and hold up a certificate of occupancy. Which profile goes where is a short list; the limits that apply on public work are shorter still.
The profiles and where each one goes
T-MOLDING REDUCER END CAP
_________ _______ ______
|___ ___| |___ \__ |___ |
floor | | floor high | | \__ low floor | | wall or
======| |====== =====| | ====== ======| | track
track track gap
STAIR NOSE THRESHOLD
______ ______
__|__ ) rounded nose ___/ \___
floor | | sill floor
======| | riser ===== =====
| Profile | Use it where | What it is doing |
|---|---|---|
| T-molding | Two floors at the same height meet, often at a doorway | Covers the gap between them; the stem drops into the gap and clips or glues into a track fastened to the subfloor |
| Reducer | A thicker floor steps down to a thinner one (hardwood to vinyl, tile to sealed concrete) | Bevels the edge of the higher floor down to the lower surface |
| End cap (square nose) | A floor stops against something vertical: a sliding door track, a hearth, a tub apron, a fixed cabinet | Covers the floor's cut edge and the expansion gap without touching the vertical surface |
| Stair nose | A floor ends at a step down or a stair landing | Gives the edge a rounded nose and covers the gap above the riser |
| Threshold (saddle) | An exterior door sill, or under a door between two rooms | Bevels on both sides between the sill or the door bottom and the floor |
Carpet adds its own edge metal: a gripper or Z-bar where carpet stretches to a hard surface, and a carpet reducer or edge trim where glue-down carpet meets a lower floor. Either way the carpet's cut edge is sealed before the trim goes on (see related: Carpet Construction for Installers).
Floating floors: the profile must not pin the floor
A floating floor moves as one panel across its whole area, and the expansion space at its edges is what lets it move. The shelf default for that space is per the maker, commonly about 1/4 to 1/2 inch, hidden by base, shoe or a transition and never pinned by a fastener; the full treatment is in Expansion Space at Walls and Fixed Objects. For transitions that means:
- The track or base fastens to the subfloor in the gap, not through the floating floor.
- The cap rests on the floor's surface and covers the gap; it is not glued or nailed to the floor.
- A T-molding at a doorway is often required by the floor maker where a room run exceeds its maximum length or where rooms meet through a narrow opening. That is a maker rule; the plank maker's instructions say when.
A transition screwed down through a floating floor is a common cause of the peaking failure worked in The Laminate That Peaked at the Kitchen Island.
The accessible level change on public jobs
Who it binds. The 2010 ADA Standards for Accessible Design apply to public accommodations and commercial facilities under Title III of the ADA and to state and local government facilities under Title II. They do not apply to a private single-family home. Many states and localities also enforce accessibility through their building code (commonly ICC A117.1 by way of the IBC as adopted), and a state code can be stricter; where two apply, the job meets both.
The limits, 2010 ADA Standards section 303:
- Up to 1/4 in vertical change: permitted with no edge treatment (303.2).
- More than 1/4 in, up to 1/2 in: beveled, with a slope not steeper than 1:2 (303.3). A 1:2 slope runs 2 units horizontally for every 1 unit of rise.
- More than 1/2 in: ramped, meeting the ramp requirements of 405 or the curb ramp requirements of 406 (303.4). A ramp's running slope is not steeper than 1:12.
Carpet (302.2). Carpet on a floor surface has a pile height of 1/2 in maximum, is securely attached, and has exposed edges fastened along their entire length with trim that meets the level-change rules of 303.
Thresholds at doors (404.2.5). Thresholds are 1/2 in high maximum, with raised thresholds and level changes complying with 302 and 303. An existing or altered threshold up to 3/4 in high is excepted where it has a beveled edge on each side with a slope not steeper than 1:2.
How to measure. Lay a straightedge on the higher surface across the transition and measure the vertical drop to the lower surface at the edge. For a bevel, measure its horizontal run as well; the slope is rise over run.
Measure the profile, not only the floors. A transition adds its own edges. A T-molding between two level floors still sits on top of them, so each side of its cap is a small level change of its own, and a square-edged cap or a threshold with a blunt edge can exceed 1/4 in vertical even when the floors match exactly. Check each edge of the installed profile against the same 303 limits: a rounded or beveled edge whose rise and run you can measure, or a vertical edge no more than 1/4 in. On a long corridor of thresholds, the profile edges are where an inspector's gauge lands.
Worked example: a lobby that meets three other floors
A tenant fit-out for a small office: the lobby gets porcelain tile whose finished surface sits 1/2 in above the slab (tile plus thinset). Three other floors meet it.
1. Lobby to carpet tile in the offices. Glue-down carpet tile sits about 1/4 in above the slab. Change: 1/2 minus 1/4 is 1/4 in, which is within 303.2 and could be left vertical. But the carpet's exposed edge needs trim fastened along its entire length under 302.2, and a trim's own lip has to meet 303 too. A carpet-to-tile reducer whose top meets the tile at its height and whose edge sits on the carpet covers both.
2. Lobby to luxury vinyl tile in the break room. The LVT is 1/8 in. Change: 1/2 minus 1/8 is 3/8 in, inside the 1/4 to 1/2 in bevel range. At 1:2 the bevel needs a horizontal run of at least 2 times 3/8, or 3/4 in. The reducer on the job has a bevel run of 7/8 in: 3/8 over 7/8 is about 1:2.3, which is gentler than 1:2 and passes. Check the other way: 7/8 in of run at 1:2 would allow up to 7/16 in of rise, and the job has 3/8.
3. Lobby to sealed concrete in the back-of-house corridor. The concrete is the slab surface. Change: 1/2 in. That is still inside 303.3 (the bevel range includes 1/2 in), so a reducer with a run of at least 2 times 1/2, or 1 in, passes.
The change that flips number 3. During layout the crew finds the slab low at the lobby edge and builds the tile setting bed up, so the tile finishes 3/4 in above the corridor. Now the change is over 1/2 in, and no bevel profile is permitted; 303.4 sends it to a ramp. At the 1:12 maximum running slope, 3/4 in of rise needs at least 3/4 times 12, or 9 in, of run: a feathered cement patch on the corridor side or a ramped profile made for the purpose. The level floors at either end serve as the ramp's landings, and at 3/4 in of rise no handrails are required (405.8 triggers them at a rise over 6 in). The alternative is to fix the slab under the tile so the tile finishes at 1/2 in and the reducer works, which is what a flatness check before layout would have caught. See related: Floor Flatness Tolerances by Floor Type.
The record. For each transition, the measured rise, the profile used, its bevel run and the slope, with a photo of a rule standing against the edge. On a public job that sheet answers the inspector's question before it is asked.
Residential jobs: the same numbers as good practice
A house is not covered by the ADA, but a 3/8 in lip is the same trip hazard in a kitchen as in a lobby, and customers planning to age in place ask for low transitions by name. Using the 303 limits as the shop's own default costs nothing extra at selection time. Where a house project is publicly funded or the customer's program requires accessible features, ask what standard the program names.
How the choice goes wrong
- Profile picked from the sample board, not the installed heights. The reducer that matched a 3/4 in solid sample does not match a 1/2 in engineered floor plus underlayment. Measure the installed floors, then order.
- Two floors that were equal on paper and are not after underlayment. A T-molding over a 1/16 in difference rocks and squeaks; a reducer would have sat flat.
- A threshold fastened through a floating floor. It pins the floor at the doorway; the floor peaks or the threshold cracks.
Removing and resetting existing transitions and thresholds is covered in How to Pull and Reset Floor Transitions and Thresholds.
References
- 2010 ADA Standards for Accessible Design, sections 302, 303, 404.2.5 and 405 (U.S. Department of Justice)
- ICC A117.1 and the IBC accessibility chapter, as adopted by your state or locality
- Flooring and transition manufacturers' installation instructions
- See related: How to Pull and Reset Floor Transitions and Thresholds; Expansion Space at Walls and Fixed Objects; Stair Riser and Tread Rules When Flooring Changes Height