What is under your stair carpet is probably not a staircase

What a carpeted stair is actually made of

Plain utility grade treads, no nosing, and often a stringer at the wall that is nothing more than framing, because none of it was ever going to be looked at.

The nosing is the rounded front edge that a finished tread projects past the riser. A stair built for carpet does not have one, because the carpet wraps the edge and does the job. That single missing detail is the clearest way to tell from a lifted corner which stair you have.

The treads themselves are usually plywood or a soft utility grade. They are structurally fine and cosmetically not a floor. And the wall stringer, the diagonal board that closes the gap between the treads and the plaster, is frequently absent entirely on a carpeted stair.

So the honest answer to can we just sand it is almost always no. There is nothing finished there to sand.

The exception, and how often it actually happens

In the oldest housing here there sometimes is a real finished stair under the carpet, usually oak and occasionally heart pine, and it happens often enough to be worth checking and rarely enough not to plan on.

This is where the age of the stock matters. Our dataset at /data/ puts Philadelphia at 40.0 percent pre-1940, and that pre-1940 band is where original finished stairs turn up under carpet that went down in the 1970s.

When it happens it is the best outcome available, because a sound original stair can be refinished rather than rebuilt, and the difference in scope is large.

It is also the reason we look before quoting rather than after. Building an estimate around hoping for it would be dishonest; refusing to check for it would be lazy.

Where the code stops being a suggestion

Adding finished treads raises every step, and Pennsylvania allows no more than 3/8 inch of variation in riser height within a flight, which is exactly what a retread threatens.

Philadelphia adopts the 2021 International Residential Code as Subcode R of the Building Construction and Occupancy Code, and Pennsylvania amends the model: the maximum riser here is 8 1/4 inches, not the 7 3/4 inches the base IRC sets. Section R311.7.5.1 also limits variation within a flight to 3/8 inch.

That variation limit is what a retread runs into. Every riser rises by the thickness of the new material, except the top and the bottom, which change by a different amount because the floor above and the floor below did not move with them. Two steps out of fourteen change differently, and they are the two people trip on.

So the thickness gets decided before material is ordered, not discovered after it is fitted. It is one of the reasons stair work is priced by the stair rather than by the square foot.

The railing has its own numbers, in their own sections, and they are laid out with citations on our stair code page.

The moment to fix the squeaks

With the carpet off and before new treads go down, the structure is open, and it is the only moment when a squeak can be reached from above without dismantling finished work.

Most stair squeaks are movement between the tread and the stringer, or a riser separated from the back of the tread. Once a finished tread is on, reaching either means removing what was just installed.

So the sequence is carpet off, structure inspected and corrected, then finished material. A crew that skips the middle step delivers a stair that looks right and talks to you every morning.

It costs almost nothing while the stair is open, and it cannot be bought back afterwards. If you take one thing from this article, take that.

How to check your own stair in five minutes

Lift the carpet at one corner of a tread, look for a rounded nosing and a hardwood surface, and then look at the underside of the stair from the basement or a closet.

Choose a tread near the top, at the wall side, where a lifted corner will not show. Carpet is held by tack strips at the back of each tread, and a corner can be eased up with pliers and pressed back down afterwards.

Look at the front edge first. A finished tread has a rounded nosing that projects past the riser below. A carpet grade tread is cut square and flush. Then look at the surface. Oak has an open, visible grain. Plywood shows its layers at the edge, and construction lumber is pale, soft and often marked with knots.

If part of the stair is open underneath, as basement stairs and closet ceilings often are, look there as well. You can see how thick the treads are and how the stair was built, which tells us a good deal before we arrive.

The three jobs it can turn out to be

Depending on what is under the carpet, the work is a refinish of the original stair, new treads and risers over the existing structure, or a rebuilt stair.

If the stair under the carpet is finished hardwood, it is sanded and refinished. That is the smallest of the three jobs and the one people hope for.

If it is carpet grade, the usual answer is new hardwood treads and risers fitted to the existing frame. The structure stays, and what you see is new. Each tread is cut to its own opening, since no two are identical in a house that has settled.

Occasionally the frame itself is the problem: undersized, damaged, or too irregular to take new treads within the limits the code sets. Then the stair is rebuilt, and that is carpentry on a different scale.

What happens to the railing

New treads usually mean the balusters and newel have to come off and go back, which makes it the natural moment to repair or replace the railing.

On many stairs the balusters are set into the treads. Replacing the treads means removing them, and they either go back into the new treads or are replaced. A newel post that has been loose for years can be anchored properly while the stair is open.

This is where the code can enter. Resetting the existing railing is generally repair. Replacing it is new work, and in Philadelphia new work is held to the 2021 residential code: a handrail between 34 and 38 inches above the line of the nosings, and no opening in the guard that passes a 4 inch sphere.

Many original railings do not meet those numbers. That does not make them illegal to keep, and it is worth knowing before deciding whether to put the old railing back or to price a new one with the treads.

Old paint on the stair in a house built before 1978

Stringers, risers and balusters under and beside the carpet are usually painted, and in pre-1978 housing disturbing that paint for pay falls under the federal lead rule.

Pulling carpet exposes paint that has not seen daylight in decades. Removing treads, cutting stringers and sanding risers all disturb it. Under 40 CFR Part 745 that work is done with containment and with dust collected at the tool.

Our dataset at /data/ puts numbers on how often this applies. Approximately 82.8 percent of Philadelphia's housing predates 1978, and across the 635 towns and neighborhoods we cover the figure is approximately 60.5 percent.

For the homeowner it changes little beyond a sealed stairwell for the duration of the work. It is a reason to ask any contractor how they intend to handle it, since a stair is open to two floors and dust travels both ways.