Stair Stringer Layout

How-to Guide Process Updated Aug 24, 2026 · Deck Building

Why this matters

A miscalculated stair stringer is the single most-common deck-build error that gets a customer hurt. The riser-to-tread proportions must be consistent and within IRC limits, and the stringer cuts must support the load. A contractor who can lay out and cut stair stringers correctly produces stairs that pass inspection, look professional, and function safely. The skill is geometry + measurement + careful execution.

What IRC requires

IRC governs stair construction:

Riser height

Maximum: 7 3/4 inch
Minimum: 4 inch (effectively)
Consistent within 3/8 inch from rise to rise

Tread depth

Minimum: 10 inch
Consistent within 3/8 inch from tread to tread

Nosing (the front projection of each tread)

3/4 inch to 1 1/4 inch beyond the riser below
Or no nosing if the riser face is angled (sloped riser allowed)

Headroom

6 ft 8 inch minimum clearance above any tread

Width

36 inch minimum for stairs leading to / from required exits

These rules ensure stairs are safe to walk; consistency matters because the user's body adapts to the rhythm of risers and treads.

Stair geometry

For each set of stairs:

Total rise: vertical distance from lower floor to upper floor
Total run: horizontal distance from start to end
Number of risers: total rise divided by acceptable riser height
Number of treads: typically one less than risers (the last "tread" is the upper landing)

Calculation example

For a deck 36 inches above ground:

Total rise = 36 inches
Try riser height 7 inches: 36 / 7 = 5.14 (round up to 6)
6 risers × 6 inches actual riser = 36 inches
5 treads × 10 inch tread = 50 inches total run

So 6 risers at 6 inch each, 5 treads at 10 inch each, total run 50 inches.

Alternative: 7 risers × 5.14 inch each, 6 treads at 11 inch each. Either works; the choice affects the slope.

The stringer

The stringer is the angled support board that holds the treads and (optionally) the risers.

Stringer material

2x12 pressure-treated lumber typical
Cut from a single board for consistency
Minimum 5 inches remaining at the throat (the narrowest point of the cut), per AWC DCA 6, the prescriptive residential wood deck guide

Stringer count

36 inch wide stairs: 3 stringers (2 outer + 1 center)
42 to 48 inch wide: 4 stringers
Wider: proportionally more
Drive the count off stringer spacing, not width alone: the spacing has to stay inside what the tread material can span

Stringer layout procedure

Step 1: Measure total rise and total run

Standing at the proposed stair location:

Measure total rise: finished deck surface down to the finished landing surface. Do not subtract anything here. The tread-thickness adjustment happens at the stringer's bottom cut in Step 5, and taking it twice leaves the bottom riser short by the thickness of a tread
Plan total run (distance the stairs will extend from the deck)

Step 2: Calculate risers and treads

Total rise divided by ~7 = number of risers (round to nearest whole number)
Number of risers minus 1 = number of treads (the upper landing is one)
Actual riser height = total rise divided by number of risers
Choose tread depth (minimum 10 inch)

Step 3: Verify code compliance

Riser height under 7 3/4 inch (maximum)
Tread depth at least 10 inch (minimum)
Consistent risers (within 3/8 inch)

Step 4: Mark the stringer

For each riser-tread pair:

Mark the riser cut (vertical) using a framing square
Mark the tread cut (horizontal) using a framing square
Verify the cuts maintain consistent dimensions

Use stair gauges (small fixtures that clip onto a framing square) to maintain consistent stair dimensions across multiple cuts.

Step 5: Account for the first tread / last tread offset

The first tread (bottom) and last tread (top) often need offset cuts:

Bottom: cut the stringer back by the thickness of the tread material (so the bottom riser is the same as the others)
Top: cut the stringer back so the top tread aligns with the deck surface

Step 6: Cut the stringer

Use circular saw to make the cuts
Finish each cut with a handsaw or jig saw (don't over-cut)
Verify the throat depth (the narrowest part of the stringer)
Cut should leave at least 5 inches at the throat for structural integrity

Step 7: Verify the stringer

Place the stringer at the planned location
Verify each cut matches the layout
Place a level on each tread cut; verify level
Check overall length

Step 8: Make additional stringers from the first

Use the first stringer as a template
Trace cuts onto the other stringers
Cut to match exactly

Step 9: Install stringers

Position stringers at proper spacing
Attach top of stringer to the deck framing (per IRC; typically with stair stringer hangers - Simpson Strong-Tie LSSH series)
Attach bottom of stringer to a footing or concrete pad
Verify all stringers are at the same level

Step 10: Install treads (and risers if used)

Cut treads to length (typically the stair width + slight overhang for the nosing)
Attach treads to stringers
Install risers if used (typical for finished interior or some exterior stairs)

Common stair errors

Inconsistent riser heights

The most-common error. One riser is taller or shorter than the others. Users trip. Inspector fails the stairs.

Fix: re-layout from scratch; cut new stringers.

Tread depth too shallow

Tread depth less than 10 inches violates code AND is uncomfortable / dangerous.

Fix: re-design with more treads or wider stairs.

Riser too tall

Riser over 7 3/4 inches violates code.

Fix: add more risers; reduce per-riser height.

Stringer throat too narrow

The cut removes too much material at the throat; structural failure.

Fix: redesign with smaller cuts or use a thicker / wider stringer.

First tread not offset for tread thickness

The bottom riser is taller than the rest because the tread thickness wasn't accounted for.

Fix: adjust the first-tread cut at the bottom of the stringer.

Stringer attachment inadequate

Stringer not properly attached to deck or footing; eventual structural failure.

Fix: use proper hardware (LSSH stringer hangers); attach to proper footing.

Number of stringers

For typical deck stairs:

36 inch width: 3 stringers (2 outer + 1 center)
42 to 48 inch: 4 stringers
Wider: proportionally more
For composite treads: may need closer stringer spacing per manufacturer

Treads (the part the foot lands on)

Material

2x12 pressure-treated lumber: typical PT stairs
Composite tread: specific manufacturer products
Custom: hardwood, exotic

Attachment

Two fasteners per stringer per tread
Galvanized or stainless steel deck screws
Pre-drill to prevent splitting

Nosing

Tread extends 3/4 to 1 1/4 inch beyond the riser
Provides better foot landing
Some prefer flush (no nosing) for modern aesthetic

Risers (the vertical board between treads)

Required or optional

IRC allows open risers in some applications
Open risers must not allow a 4 inch sphere to pass through
For most exterior decks: open is acceptable

When to install closed risers

Open risers are acceptable on most exterior deck stairs, but several situations turn closed risers from a style choice into the right call.

Close them when:

Accessibility requirements apply. Where a stair has to meet accessibility criteria, open risers are not permitted and the nosing profile is regulated so a toe cannot catch on the way up. Confirm the applicable requirement before you lay out the stair, not after.
Small children or pets use the stair. Small feet slip through an open riser, and children carry things that fall through. It also reads as safer to a nervous user, which matters more than it sounds.
The stair is tall. A long run high off grade feels open and unsteady to many people. Closing the risers changes how the stair is used more than any handrail upgrade.
The space under the stair is used. Seating, a walkway, storage, or a patio underneath means every dropped item, every bit of dirt swept off a tread, and most of the rain hitting the stair ends up down there. Closed risers stop it.
The stair connects to a finished or formal entry where an open stair looks unfinished next to the rest of the work.

Leave them open when:

The stair sees snow and ice. Open risers let snow fall through instead of packing onto the treads, and they drain and dry faster. In a hard-winter climate this is a genuine safety argument for open.
The stair is in a wet, shaded, or leaf-heavy location where debris would otherwise sit trapped in the corner between riser and tread and hold moisture against the lumber.
The design intent is modern and none of the conditions above apply.

If you close them:

Use pressure-treated stock or the deck board manufacturer's matching riser product, not interior trim.
Fasten the riser to the stringers. It is not a structural member and the treads should not be carrying it.
Set the riser back slightly behind the tread nosing so the nosing still projects and water runs off the tread rather than down the riser face.
Leave the tread-to-riser joint able to drain rather than sealing it tight. A sealed joint on an exterior stair holds water and rots the tread from underneath.
Keep the code limits in mind whichever way you go: consistent riser heights, minimum tread depth, and on an open stair the opening cannot pass the sphere the code specifies.

References

IRC R311.7 (Stairways: riser, tread, headroom, width, handrails).
IRC R312 (Guards).
IRC R507 (Decks).
AWC DCA 6, Prescriptive Residential Wood Deck Construction Guide (stringer throat, stringer spacing).
Manufacturer literature: Simpson Strong-Tie stringer hangers.
Manuall internal: Deck Building Composite vs PT Lumber, Deck Building Joist Hanger Selection.