Deck stair layout
Every stringer on a stair must be identical, and the way to guarantee that is to cut one, check it against the actual grade, and use it as a template for the rest. The layout itself is two numbers repeated down a board.
The two numbers
Riser height and tread depth. Both come from the total rise and run:
- Risers = ⌈total rise ÷ 7.75⌉, because 7¾″ is the code maximum.
- Riser height = total rise ÷ risers. All risers equal, including the bottom one.
- Treads = risers − 1, because the top tread is the deck surface.
- Tread depth = total run ÷ treads.
For a 36″ rise: 5 risers at 7.2″ each, 4 treads. With a 44″ run, each tread is 11″.
Marking the stringer
Use a framing square with stair gauges set at the riser height and tread depth. On a 2×12:
- Set one gauge at 7.2″ on the tongue and one at 11″ on the blade.
- Place the square so the tongue is vertical and the blade horizontal, with the corner at the top edge of the board.
- Mark both legs. That is the first riser cut and the first tread.
- Step the square down the board, marking each pair, until you have all the notches.
- Cut to the marks, stopping the cut at the inside corner — over-cutting weakens the stringer at exactly the point that carries the load.
The first mark has to allow for tread thickness
The step down from the deck surface to the first tread is a riser, and the tread sits on top of the notch. So the top notch is dropped by the thickness of the tread material — usually 1″ for a 5/4 board — or the first riser will be one tread thickness short.
This is the single most common stringer error, and it produces exactly the defect the code cares about: a first riser that differs from the others.
Notch depth limit
IRC R502.10 limits notching of solid sawn stringers to one-quarter of the depth. On a 2×12 at 11¼″, that is about 2.8″. The notch cut for a riser is not a notch in that sense — it is the profile of the stair — but the remaining depth under the notch is limited by the same logic, and a stringer with less than 3½″ left under the seat should not be used.
If the geometry does not leave enough, the answer is a deeper board (2×12 is the practical maximum), a shallower riser, or a landing that splits the flight.
Cut one, fit it, then copy
Set the first stringer in place against the deck and the grade before cutting the others. Check:
- The top of the stringer meets the deck frame without a gap.
- The bottom sits on grade or on a landing, not floating.
- All risers measure the same, including the bottom one.
- All treads measure the same.
Grade is never exactly where the drawings say. Adjust the bottom of the stringer — cut it shorter or add a small pad — and then template the rest from the fitted stringer. Cutting three from the same marks before checking one is how a stair ends up with a short bottom riser.
Spacing and attachment
Three stringers for a 36″ wide stair, four above 48″. Attach them to the deck frame with a hanger or a bolted ledger, not with screws through the rim. The bottom of each stringer needs a bearing surface: a concrete pad, a treated board on grade, or a stake-driven ground anchor.
Where this guide hands off to a calculator
- It does not size the stringer — see the stringer calculator.
- It does not cover winders, spirals or curved stairs, which are laid out differently.
- It does not cover the handrail, which has its own height and mounting rules.
- It does not replace the code dimensions in deck stair code.
Questions people actually ask
How do I lay out stair stringers?
Divide the total rise by the number of risers to get the riser height, divide the run by the tread count to get the tread depth, then step a framing square down the board at those two settings.
Why is my bottom step shorter than the rest?
Because the top notch was not dropped by the tread thickness, or because the grade is higher than assumed. Always fit one stringer to the actual grade before cutting the others.
How many stringers for a 36 inch wide stair?
Three. Two is acceptable up to about 30 inches; four is usual above 48 inches, and some jurisdictions require them at 16-inch centres regardless.
Can I cut stringers out of a 2x10?
Only on a shallow stair. The notch removes depth, and a 2×10 at 9¼ inches leaves too little material under a typical 7-inch riser. Use a 2×12.