How to Install Carpet on Stairs
Why this matters
A stair is the hardest-worked carpet in the house and the one place a loose install can put someone on the floor. Every trip down plants a heel on the nose and pushes the carpet toward the edge, so carpet that is not hooked tight in the crotch creeps forward until it rolls under a foot. Stairs are also where workmanship is most visible: a gap at the crotch, a sagging riser or a nose that moves under a thumb reads as a cheap job from the bottom of the flight.
Riser height rules when the floor build-up changes belong to 'Stair Riser and Tread Rules When Flooring Changes Height'. The general strip and cushion method is 'How to Install Tackless Strip and Carpet Cushion'. This card covers what changes on a stair.
Two methods, and how to pick
WATERFALL
| upper
riser strip -> r riser
pins down |
carpet ~~~~~~~~~~~~~~~~~~~~~~~~~~+ crotch
cushion :::::::::::::::::::: t |
tread ======================t===+
nose ( tread strip, pins
|~ toward the riser
| ~ carpet drops straight
| ~ from the nose to the
| ~ crotch below, clear of
| the riser face
lower riser
CAP-AND-BAND (UPHOLSTERED)
carpet ~~~~~~~~~~~~~~~~~~~~~~~~~~+ crotch
cushion :::::::::::::::::::: t |
tread ======================t===+
nose (~
|~ carpet wrapped tight
|~ under the nose, stapled
|~ beneath it, then held
|~ tight down the riser
lower riser
Waterfall. The carpet goes over the nose and falls straight to the crotch of the step below, leaving a small air space in front of the riser. It is faster, suits thicker cut piles that will not bend tightly, and is the common choice on closed stairs. Its weakness: the free-hanging riser section can look loose on a stair with a deep nose overhang.
Cap-and-band, also called upholstered. The carpet is pulled tight under the nose, stapled up underneath it, and held tight down the riser face, so it follows the profile of the stair. It looks tailored and shows the nose shape; it takes longer, wants a carpet that bends tightly without the backing showing at the fold, and needs nose staples that hold.
Pick with the customer, on a sample folded over a real nose. A heavy plush that grins (shows backing at the bend) when folded tight is a waterfall carpet whatever the customer pictured.
Step 1: Measure each step, not the stair
Stairs are rarely uniform. Measure each tread's width at the front and the back and each step's carpet path: run a flexible tape from crotch to crotch along the route the carpet will take, over the nose for the method chosen. Write the numbers on the tread in pencil.
Why each one. A single measurement times the number of steps produces pieces that fit the stair on average and none of its steps exactly. The skirt boards on a site-built stair can wander by more than a trim allowance can absorb.
Step 2: Plan the cut with the pile running down
Cut each step's piece, or a continuous runner, so the pile lays down the stair, toward the nose on the tread and down on the riser, which is what CRI 105, the residential installation standard, calls for in substance. Pile running up the stair catches on heels, wears faster at the nose and reads as a different shade from the landing.
Step 3: Set the strip for a tight crotch
On each tread, set tackless at the back with pins toward the riser. On each riser, set tackless at the bottom with pins pointing down. Set each strip back from the crotch so that, with carpet in place, the folded carpet fills it: the shop gauge is a scrap of the actual carpet folded double, laid in the crotch, with each strip butted to it.
Why that gauge. Two layers of carpet end in each crotch, the piece coming up off the lower step and the piece going down to it. Strips set too close to the crotch leave no room and the carpet bridges over a gap; set too far back, the carpet drops into a groove you can see.
Step 4: Cushion the treads only
Cut cushion to each tread, from the front edge of the tread strip to the nose, wrapped over the nose and stapled underneath it. Do not cushion the risers. Use the cushion the carpet maker allows on stairs, which is often firmer or thinner than its room cushion; see 'Carpet Cushion Types and the Maker's Cushion Spec'.
Why firm on the nose. A thick, soft cushion rounds and softens the nose, so the edge a descending foot reads is no longer where the step actually ends. That is a fall risk, not only a wear problem.
Step 5: Work from the bottom up, stretching over each nose
Each piece covers one riser and the tread above it. Starting at the bottom:
- Bottom edge. Tuck the piece's bottom edge into the crotch onto the riser strip, with a stair tool and hammer. At the floor, either tuck it into the floor carpet's crotch or, on a hard floor, turn the edge under or bind it and staple it.
- Riser. Waterfall: bring the carpet straight up to the nose. Cap-and-band: pull it tight up the riser and staple it under the nose, staples hidden in the fold.
- Nose and tread. Wrap it over the nose, then set the knee kicker on the tread with its head near the nose and kick toward the riser, pulling the carpet tight over the nose and onto the tread strip.
- Crotch. Drive the carpet into the crotch with the stair tool so it seats on the tread strip and folds down into the crotch, then trim it to leave the tuck the next piece's bottom edge will share.
- Sides. On a closed stair, trim the edges at the skirt boards and tuck. On an open side, turn the edge under and staple it, or have it bound before install.
Why kick toward the riser. Every footstep pushes the carpet the other way, toward the nose. The tread strip's pins lean toward the riser to resist exactly that pull.
Hazard. Working on a stair in use is a fall risk to the crew and the household. Close the stair to the family while work is underway, keep tools and loose strip off the treads below you, and fire the staple gun only with the free hand behind the nose and out of line with the staple. Tackless pins on the treads puncture hands and feet: wear gloves, and do not leave a stair with exposed strip overnight.
Worked example: a closed straight stair
The stair. 13 risers at about 7-1/2 in, 12 treads at a 10 in run with a 1 in nose overhang, closed by skirt boards both sides, 36 in between them on every tread but one when measured front and back. The landing carpet already wraps the landing nose and runs down riser 13 to the crotch at the back of tread 12. So there are 12 pieces, piece n covering riser n and tread n. The customer chose waterfall for a thick cut pile that grinned when folded tight.
Piece size. The flexible tape, crotch to crotch over the nose on a typical step, read 19 in. With 1-1/2 in added at each end for the tuck and trim, each piece is cut 22 in long. Width is 36 in plus 1 in each side, 38 in.
Off the roll. The roll is 12 ft, 144 in wide. Each piece's 22 in length runs along the roll, so the pile lies down the stair, and three pieces sit side by side across the width: 3 x 38 in is 114 in, leaving a 30 in strip. Twelve pieces at three to a row is 4 rows, 4 x 22 in = 88 in of roll. The crew cut a fifth row as spares, since a miscut piece otherwise means waiting on the same dye lot: 5 x 22 in = 110 in of roll, about 9 ft 2 in.
The run. Pieces 1 to 12 went in from the bottom up. On tread 7 the measured width was 36-3/8 in at the back, so its piece was trimmed to that tread, not to the stair. Riser heights were unchanged in the middle of the flight, because every tread gained the same carpet and cushion thickness; the bottom riser, meeting a hardwood hall floor, was checked against 'Stair Riser and Tread Rules When Flooring Changes Height', and the difference fell within it.
What changes the answer
- A continuous runner instead of pieces. One length runs the whole flight, folded at each crotch. It uses less carpet on a narrow stair and has no cross seams, but a mistake on step 9 is a mistake in the whole run, and the length has to include the full crotch-to-crotch path of every step plus the folds. On a stair whose steps measured differently, pieces fit better.
- Winders and pie-shaped steps. Each wedge gets its own piece, cut with the pile running toward that step's nose, which is not parallel to the straight steps' direction. Pattern-matched carpet on winders is a template job, with the shape traced in paper before cutting.
- A runner with exposed wood at the sides. The edges are bound or serged before install, the strip is cut short of the runner's width so no pins show beside it, and the visible wood margin has to come out equal on both sides on every step, which means measuring from each skirt rather than from the runner.
How to check you got it right
- Tight treads: grab the carpet mid-tread and try to slide it toward the nose: it does not move.
- No gaps at the crotch: look down the flight from the top in normal light: no strip, backing or groove showing at any crotch.
- Nose snug: press the nose with a thumb and stand with a heel on it: the carpet does not roll or slide over the edge.
- Pile down: brush each tread toward the nose: it lies smooth on every step, the same shade as its neighbors.
- Edges: clean at every skirt board, no fraying, no staples visible.
A stair that passes all five is tight enough that the household's first hundred trips down will not move it.
References
- CRI 105, the Carpet and Rug Institute's installation standard for residential carpet, on stair installation and pile direction; check the current edition
- The carpet and cushion makers' installation instructions for stairs
- See related: Stair Riser and Tread Rules When Flooring Changes Height; How to Install Tackless Strip and Carpet Cushion; Carpet Cushion Types and the Maker's Cushion Spec