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Stair Stringer Layout

How-to Guide Process Updated Jul 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)

Stringer count

  • 36 inch wide stairs: 3 stringers (2 outer + 1 center)
  • 42 inch wide: 4 stringers
  • Wider: proportionally more

Stringer layout procedure

Step 1: Measure total rise and total run

Standing at the proposed stair location:

  • Measure total rise (deck height - 1 1/2 inch for the first tread offset)
  • 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:

  1. Mark the riser cut (vertical) using a framing square
  2. Mark the tread cut (horizontal) using a framing square
  3. 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 to 42 inch width: 3 stringers (2 outer + 1 center)
  • 42 to 48 inch: 3 or 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

References

  • IRC R311.5 (Stairways).
  • IRC R311.7 (Stair construction).
  • IRC R314 (Smoke alarms in stair areas).
  • IRC R507 (Decks).
  • Manufacturer literature: Simpson Strong-Tie stringer hangers.
  • Manuall internal: Deck Building Composite vs PT Lumber, Deck Building Joist Hanger Selection.

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