Carpeted stairs to wood: what thicker treads do to the first and top step

Taking carpeted stairs to wood changes the height of the first and the top step, and those two are where the job goes wrong. Put a 19 mm wood cap on every tread and the steps in the middle stay as they were, because each one moves up by the same amount. The bottom step gains 19 mm and the top step loses 19 mm, unless the floors at each end rise too.

Your foot learns the height of a stair after a step or two, and it expects the next one to match. Ontario's code allows very little difference. So the order of work is a tape measure, then some subtraction, and only then an order for treads. All of it can be done with the carpet pulled back and a pencil.

Where does the extra height go?

Each cap lifts the tread it sits on. A middle rise is measured from one tread up to the next, and both have moved, so nothing changes. The first rise starts on a floor that hasn't moved. The top rise ends on one.

How much difference does Ontario allow between two steps?

Very little: 5 mm between neighbouring risers and 10 mm between the tallest and shortest in one flight. The City of Markham prints the wording of Article 9.8.4.4 in Builder Tip 54, updated to the 2024 code. Treads get the same two limits for their run.

The rise is measured from nosing to nosing, the front edge of one tread to the front edge of the next. Now take a flight with 190 mm rises and watch what happens. That figure is only an example for the arithmetic, so use your own numbers.

What should you measure once the carpet is back?

Do this before anyone quotes a tread, and write the results on one sheet.

1. Pull the carpet and pad back on the first two and last two steps, and on a stretch of floor at each end.
2. Measure every rise from nosing to nosing, on the same side of the stair. Older houses often have a rise or two that is already off.
3. Measure each run the same way, then the depth of a tread. Markham's tip says a tread's depth can't be more than its run plus 25 mm, which limits how far a new nosing can stick out.
4. Find the real thickness of each finished floor you plan: boards and underlay, or tile, its bed and any membrane.
5. Press on every tread and listen. A tread that moves gets fixed to the stringer before anything covers it.
6. For the first rise, add the cap and subtract the new lower floor. For the top rise, subtract the cap and add the new upper floor. Compare the results with your middle rises, against 5 mm and 10 mm.

How do you fix a first or top rise that comes out wrong?

Change something at the end of the flight that is out, or change the thickness going on the treads. Which one suits your stair depends on what the numbers from your sheet say and on how far along the floors are.

Raise or lower the floor build-up

This is the simplest fix while the floors are still being chosen. Boards with a thicker or thinner underlay, or a different tile bed, can bring a rise back inside the limit. Just check door bottoms and thresholds along the same floor, since those move with it.

Choose a different tread thickness

A thinner cap reduces the problem at both ends. If the floors aren't changing, taking the old treads out and fitting new ones of the same thickness removes it altogether.

Lift the stair on shims

Markham's Builder Tip 7 on stairs over ceramic, porcelain or marble calls the first riser critical, and it describes shimming under the stair or oversizing that riser to allow for the full thickness of the floor. That detail is drawn for a stair going in over a planned floor. On a stair already in place it means opening things up, so it belongs in the quote from the start.

Rebuild the flight

When the rises were already far apart under the carpet, or the floors change by a lot, a new set of stringers can share the total height evenly across every step. Run becomes part of the same decision: Markham's Builder Tip 106 gives a minimum run of 255 mm for permits issued for houses since January 1, 2022, and a stair built before that could have a shorter one.

What else moves when the treads get thicker?

Everything measured from the nosing or the floor. A rail stays where it was while the steps come up under it, so a stair that was close to a limit can go past it.

Sources: Township of Centre Wellington's notice on the stair changes for the handrail, and a hyperlinked copy of the code's January 2025 compendium for guards, clear height and openings. That copy is not a government site, so have your building inspector confirm a figure your job depends on.

Do you need a permit to change a stair in Toronto?

Ask Toronto Building before you start if the framing, the layout or a guard is changing. The City's interior alterations guide tells applicants to detail stairs, landings, guards and handrails in their drawings, and to show how a guard connects. It doesn't draw a line for a stair that is only being re-covered, so get that answer for your own job. Our post on which Toronto renovations need a permit covers the wider question.

Which comes first, the floor or the stairs?

The decision on both comes first, and it's the same decision. After that, the work usually runs in this order:

1. Choose the floor at each end and the tread thickness, then run the arithmetic above.
2. Repair and fasten the old stair, or rebuild it if the numbers call for that.
3. Lay the floors, as in our flooring installation work, which plans stair nosings together with the rooms around them.
4. Fit treads, risers, skirt boards and newels. These are custom carpentry, cut to each step since no two openings measure quite the same.
5. Set the rail and the balusters from the finished nosings, then measure each height again.
6. Paint the risers, stringers and walls last, the way we handle stairwells and railings on a painting job.

Measure one more time after the first tread and the top tread are dry-fitted, before any glue goes on. A rise that's 2 mm off on paper is easy to correct at that point, and it's a rebuilt step once the finish is on.