Stringer (Stair)
The sloped structural member that supports the treads and risers of a stair.
Quick Answer
A stair stringer is the inclined structural member that supports the treads and risers of a stair. Wood stringers are cut with a sawtooth notch or hold treads in a housed groove, and steel stringers are channels or plates. Estimators count them by the piece, usually as part of a stair package.
The Full Picture
A stringer is the sloped beam of a stair. It carries the treads, risers and the live loads on them down to a floor, a landing or a foundation. A cut stringer has notches sawn along its top edge so the treads sit on the steps. A closed or housed stringer has grooves that capture the tread and riser ends, and a stringer can also be a straight board that treads are fastened to. Steel stairs use channel or plate stringers with welded or bolted treads, which are fabricated and often supplied by a metals shop.
In the building, stringers sit between the upper and lower floor framing, and they bear on a header, ledger, landing or slab. Stair sections and details show the rise, run and number of treads, and the stringer size is often called out there or in the structural notes. A stair needs three or more stringers when treads are wide, and a stair with open sides may have finish stringers, called skirt boards, on the walls. OSHA's stairway rule covers temporary stairs used during construction, and permanent stair geometry comes from the code and drawings.
The unit is each, by stringer and by stair. A stringer is counted by piece with its length. The length is the sloped length, which is the square root of (total rise squared plus total run squared), plus whatever the layout needs for the top and bottom cuts. The stringer material, such as a 2x12 in wood, is picked so the depth left under the notches is enough, and stock length is chosen to fit the sloped length. Steel stringers are priced each, or by weight with the rest of the metals. Stringers are normally part of a stair package that includes treads, risers, rails and finishes.
Typical pricing mistakes are using the plan length instead of the sloped length, forgetting the center stringer on a wide stair, missing the finish stringers, and not noting that wood and steel stairs belong to different trades. Another is leaving out the landing framing and the posts that support the stair at an intermediate level. The estimator should confirm who carries the stair as a unit, since carpentry, metals and millwork trades may all be involved.
Real Examples
Common Misconceptions
People assume: A stringer is the same as a stair tread.
Actually: Stringers are the inclined supports. Treads are the horizontal walking surfaces that sit on them.
People assume: Stringer length equals the horizontal run of the stair.
Actually: It is the sloped length, which is longer, and needs extra for the cuts at each end.
People assume: Two stringers are always enough.
Actually: Wide stairs and heavier treads often need a center stringer, and the details or structural notes say how many.
Does MeltPlan Solve This?
Partially — adjacentStair rise, run and flight counts come from plans and sections, and MeltPlan's takeoff service applies to measuring from them: AI pulls quantities from plans and US-based experienced estimators review and adjust them. Stringer sizing, trade assignment and finish details stay with your estimator.
Get stair counts and dimensions taken off your plans →Frequently Asked Questions
What is a stair stringer?
It is the inclined structural member that supports the treads and risers of a stair, made of notched or housed wood, or steel channel or plate.
How are stair stringers counted?
By the piece, per flight, with the sloped length. They are often included in a stair package with treads, risers and rails.
How do you calculate stringer length?
Take the square root of the total rise squared plus the total run squared, then add for the end cuts and the material needed for the notches.
Who installs stair stringers?
Wood stairs are framed by the carpenter or a stair shop, and steel stairs are supplied and installed by a metals trade, so the trade split should be set in the bid.