How to Install Hard-Surface Treads and Risers on a Stair

Why this matters

Swapping a carpeted stair for wood treads is one of the best-looking jobs a flooring shop sells and one of the easiest to get dangerously wrong without a single bad cut. People climb stairs by rhythm: after two or three steps the body expects every riser to be the same height, and a riser that is off by more than a small fraction of an inch catches a toe or a heel. Most of the time the odd riser is the top or the bottom one, created not by the stair work but by a floor at one end changing thickness while the other does not. That has to be found with a tape before the old treads come out, not with a foot after the new ones go in.

The code figures and the reasoning behind them belong to 'Stair Riser and Tread Rules When Flooring Changes Height'. This card is the measuring and the install.

Before you start

Start state. You know what floor goes at the top and at the bottom of the flight, and its finished thickness. You have the new treads and riser stock, polyurethane construction adhesive, trim-head screws or finish nails with matching plugs or putty, a tread template gauge, shims, and a saw that can cut flush to a riser.

Hazards. A stair under construction is a fall hazard to the whole household: close it, provide another route, and never leave it overnight with treads missing or loose. Pre-1978 painted skirt boards, stringers and risers that will be cut, scraped or sanded fall under 'EPA Lead RRP Rule for Contractors' and 'Lead-Safe Rules for Floor Work in Pre-1978 Homes' before anyone cuts them. Cutting old treads and new oak makes fine wood dust: cut with dust extraction, and where dust cannot be controlled at the tool, use respiratory protection under a written program per 29 CFR 1910.134 (applied to construction work by 29 CFR 1926.103). Wear eye protection when prying out old treads, which tend to split and throw nails. Read the adhesive's SDS for its vapor and skin warnings, ventilate, and wear the gloves it names.

Step 1: Measure every riser before you touch anything

Measure the rise of every step from the top of one walking surface to the top of the next, at the center and at both sides, and record it. Measure the bottom riser from the finished floor below, and the top riser to what will be the finished floor above, which on a landing currently under carpet means measuring to the subfloor and adding the new floor's thickness. Measure each tread's run nose to nose and its nose overhang.

Why all of them. Old stairs are seldom uniform, and the carpet hid it. If riser 4 is already 1/4 in taller than its neighbors, the shop needs to know that before the job, not after the customer trips on it and the new treads take the blame.

Step 2: Compute the after, not just the before

For each riser, write the after height: the before height, plus what the tread above it gains, minus what the tread below it gains. Middle risers stay the same whenever every tread gains the same thickness, which is why stair problems collect at the ends. The bottom riser changes by what the first tread gains minus what the lower floor gains; the top riser by what the upper floor gains minus what the last tread gains.

Check the after column against the figures the stair rules card carries for the IRC as adopted, in the 2021 edition numbering: no riser over 7-3/4 in (R311.7.5.1), and the tallest riser in the flight no more than 3/8 in taller than the shortest. Where tread depth is under 11 in, the nose overhang stays between 3/4 in and 1-1/4 in (R311.7.5.3). Your jurisdiction's adopted code governs, and an existing stair being refaced may be treated differently from new construction; ask the building department before planning around that.

Step 3: Choose caps or full replacement from the numbers

Caps. The old bullnose is cut off flush with the riser and a retrofit tread of a stated thickness is glued and fastened on top of the old tread. Every tread gains the cap's thickness. Fast, keeps the original structure, and adds a fixed amount to every tread.

Full replacement. The old treads come out entirely and new solid treads sit on the stringers. The tread top can be set where the plan needs it, within reason, by shimming on the stringer cuts. It takes longer, it needs open (cut) stringers to shim on, and a stair with routed, housed stringers cannot have its treads raised this way: that is a carpenter's rebuild.

Step 4: Fit each tread to its own opening

Use a tread template gauge on every step, or scribe each opening: skirt boards on a site-built stair are rarely parallel, and a tread cut square to a 36 in nominal opening leaves a visible gap at one end or will not go in. Cut, dry-fit, and number every tread and riser on its underside. Fit risers first, since each riser's height is set by the treads either side of it.

Step 5: Glue, shim and fasten, bottom up

Install riser 1, then tread 1, then riser 2, and so on. Run a bead of polyurethane construction adhesive on each stringer and on the riser's top edge, set the shims the plan calls for, set the tread, and fasten it into each stringer with trim-head screws or finish nails, countersunk and plugged or filled. Each riser stands on the back of the tread below it. Fasten each riser to the stringers and, where the underside is reachable, screw up through the back of the tread below into the riser's bottom edge.

                               | new riser n+1,
                               | set on the back
  nose overhang                | of tread n
  |<- 1 in ->|                 |
  (============================+====
   new tread n, 1 in oak, glued
   and screwed to each stringer
  -----------+----------------------
             | adhesive bead and the
             | plan's shim on each
             | stringer cut
             |
             | new riser n, set on
             | the back of tread n-1
  ===========+====
   tread n-1

Why glue and fasteners both. Fasteners alone loosen as the wood moves and the stair starts to squeak; adhesive alone has nothing to hold the tread while it cures. A tread bedded in adhesive with full contact on every stringer, and pulled down by fasteners, does not move or talk.

Step 6: Finish the landing nose

Where the landing gets a plank floor, the stair nose is a flush nosing made to match it. Over a floating floor, the nosing is glued and fastened to the subfloor, never to the floating planks, and the floor keeps its own expansion space behind it, per 'Expansion Space at Walls and Fixed Objects'. A nosing fastened through a floating floor pins it and can buckle the landing.

Worked example: hardwood on the landing, tile staying in the hall

The stair. 13 risers, measured at 7-3/8 in each after the carpet came up, within 1/16 in side to side; 12 treads of 1 in particleboard with a 10 in run and a 1 in nose overhang; open stringers under a drywall skirt. Total rise is 13 x 7-3/8 in = 95-7/8 in.

The ends. The hall below keeps its tile. The landing above gets 3/4 in solid hardwood on its subfloor.

Plan A fails. The bottom riser goes to 8-1/8 in: over the 7-3/4 in maximum, and 3/4 in taller than its neighbors against a 3/8 in limit. The caps add 3/4 in to tread 1 and the tile adds nothing, so the whole change lands on one step.

Plan B spreads it. The landing hardwood raises the total rise from 95-7/8 in to 96-5/8 in. Divided by 13, that is about 7.43 in, so the plan sets 12 risers at 7-7/16 in (12 x 7-7/16 = 89-1/4 in) and the last at 96-5/8 minus 89-1/4 = 7-3/8 in. New 1 in oak treads replace the old 1 in treads, so each tread's top moves only by its shim, and tread n has to rise n x 1/16 in: 1/16 in shims under tread 1, 3/4 in under tread 12. Risers are cut to each new opening. Check: tallest 7-7/16 in, under 7-3/4 in; tallest minus shortest is 1/16 in, inside 3/8 in.

What else moved. The nosing line now climbs 3/4 in more over the flight than before, so the wall-mounted handrail sits up to 3/4 in lower above the nosings at the top. Measured at the top nose, it had been 35 in and is now 34-1/4 in, still inside the 34 to 38 in range of IRC R311.7.8.1 as adopted. Had it been 34-1/2 in before, the rail brackets would have moved too.

The install. Treads were templated one by one; tread 9's opening was 3/16 in wider at the back than the front, and its tread was cut to that. Shims were set and marked on the stringers before any adhesive went on, so nobody worked out n/16 in at a glue bead with the clock running.

How to check you got it right

• Measure every riser again, center and both sides, and write the after column beside the plan. On this stair: 1 through 12 at 7-7/16 in, 13 at 7-3/8 in, every reading within 1/16 in of plan.
• Nose overhang: 1 in on every tread, inside 3/4 to 1-1/4 in.
• No movement: stand on each tread at the nose and at each end, and rock: no deflection, no squeak, no gap opening at the riser.
• Landing nose: fastened solid, flush with the landing floor, the floating floor's expansion space open behind it.
• Walk it up and down at normal pace, then have someone who has not worked on it do the same. Nobody should feel a change in rhythm anywhere in the flight.

The measured after column goes in the job record with the before column, since it is the shop's answer if a fall is ever blamed on the stair.

References

• International Residential Code R311.7.5.1, R311.7.5.3 and R311.7.8.1 (2021 edition numbering), as adopted by your jurisdiction; check the current adopted edition with the building department
• 29 CFR 1910.134, respiratory protection (29 CFR 1926.103 applies it to construction)
• See related: Stair Riser and Tread Rules When Flooring Changes Height; Expansion Space at Walls and Fixed Objects; Lead-Safe Rules for Floor Work in Pre-1978 Homes; EPA Lead RRP Rule for Contractors