Deck Stairs Code & Construction — IRC R311.7
Lay out deck stairs that pass inspection: legal rise and run, stringer sizing, tread material, landings, handrails, and guards — plus what each choice costs.
Stairs are where most deck inspections fail, because the code is precise and unforgiving: a riser 1/2 inch too tall, a tread an inch too shallow, or a missing handrail all stop the inspection. The geometry is fixed by IRC 2021 R311.7 and the guards/handrails by R312, and getting them right on paper before you cut a single stringer saves the most expensive rework on the whole project. This guide covers the exact code numbers, how to lay out stringers, tread material trade-offs with 2026 pricing, and the handrail/guard rules that catch DIYers.
The non-negotiable stair geometry (IRC R311.7)
Every residential stair — including exterior deck stairs — must hit these limits. They are not suggestions; inspectors carry a tape and a level.
| Dimension | Code limit (IRC R311.7) |
|---|---|
| Maximum riser height | 7¾" |
| Minimum tread depth | 10" (nosing to nosing) |
| Minimum stair width | 36" (above the handrail) |
| Max variation between risers | 3/8" across the whole flight |
| Max variation between treads | 3/8" across the whole flight |
| Minimum headroom | 6'-8" |
| Nosing (closed risers) | ¾" to 1¼" projection |
How to lay out the stringers
- Measure total rise — finished deck surface down to the finished landing surface (include the landing pad thickness). Default deck height is around 36".
- Divide total rise by 7.5" and round to the nearest whole number — that's your riser count. Example: 36" ÷ 7.5 = 4.8 → 5 risers.
- Divide total rise by the riser count for actual riser height. 36" ÷ 5 = 7.2" per riser — under the 7¾" max. ✓
- Treads = risers minus 1 (the deck surface is the top 'tread'). 5 risers → 4 treads.
- Run = tread count × tread depth. At 10.5" run each, 4 × 10.5 = 42" total horizontal run.
Cut stringers from 2×12 — it's the recommended size because a notched 2×10 leaves too little material behind the cut (code wants ~5" of uncut stringer depth). A 2×12 keeps enough throat after the notches.
Tread material — cost vs maintenance
Treads take the most wear and the most weather of any deck surface. 2026-Q1 retail per linear foot of tread:
| Tread material | Price / lf | Notes |
|---|---|---|
| Pressure-treated 2× | $2.95 | Cheapest; needs annual stain on the treads |
| Composite (Trex / TimberTech) | $6.50 | No maintenance; match deck surface; tighter stringer spacing |
| Hardwood (Ipe / Cumaru) | $8.95 | Premium; pre-drill every screw; 25+ yr life |
Composite treads usually require 12" o.c. stringer spacing (vs 16" for wood) because of how composite deflects under a point load at the tread edge — check your brand's stair spec, it overrides the lumber default.
Open vs closed risers
A closed riser has a board behind each tread (kick-back). An open riser leaves the gap visible from below — popular for a modern look. The code rule:
- Open risers are allowed ONLY if a 4" sphere cannot pass through the opening (IRC R311.7.5.1).
- In practice that means risers over ~4" tall need either a closed riser board or a partial back-stop.
- Closed risers are the residential default and the safe choice for kids and pets.
Landings — the step everyone forgets
IRC R311.7.6 requires a landing at the bottom of the stairs at least as deep as the stair is wide (minimum 36"). The landing must be a firm, level surface — bare soil doesn't qualify.
- A concrete pad, paver pad, or compacted gravel pad all satisfy the requirement.
- Maximum vertical rise for a single flight before a landing is required: 12 feet (R311.7.3).
- The landing can't slope more than 2% (¼" per foot) for drainage.
Handrails and guards (IRC R311.7.8 + R312)
Handrail
- Required on at least one side when the flight has 4 or more risers.
- Height: 34" to 38" measured vertically from the tread nosing.
- Must be graspable — a 1¼" to 2" round profile, or an equivalent Type II graspable shape. A flat 2×4 on edge is NOT a code handrail.
- Must be continuous the full length of the flight and return to a post or wall at the ends.
Guards on the stairs
- Required where the stair is more than 30" above grade (R312.1.1).
- Stair guard height: minimum 34" (lower than the 36" deck guard, measured from the nosing).
- Openings: a 4⅜" sphere must not pass through the guard infill on the stairs.
- The triangular opening at the tread/riser/bottom-rail must not pass a 6" sphere.
What a deck stair flight costs
A typical 36"-rise, 42"-wide flight (5 risers, 4 treads, three 2×12 stringers) runs roughly:
- PT lumber, site-built: ~$120–$220 in materials
- Composite treads on PT stringers: ~$280–$450 in materials
- Add a landing pad: $90–$300 depending on gravel vs concrete
- Contractor labor for a short flight: $400–$900 installed
Frequently asked questions
What is the maximum riser height for deck stairs?
7¾ inches per IRC R311.7.5.1. Every riser in the flight must also be within 3/8 inch of every other riser. Most builders target 7 to 7.5 inches so there's margin and the steps feel comfortable. Divide your total rise by 7.5 and round to a whole number to find the riser count.
What is the minimum tread depth on deck stairs?
10 inches measured nosing-to-nosing per IRC R311.7.5.2. Deeper treads (10.5–11 inches) are more comfortable for descending. Tread depth times the number of treads gives your total horizontal run, which determines how far the stairs project from the deck.
Do deck stairs need a handrail?
Yes, on at least one side whenever the flight has 4 or more risers (IRC R311.7.8). The handrail must be 34–38 inches above the tread nosings, graspable (1¼–2 inch round or equivalent), and continuous for the full flight. A flat 2×4 laid on edge is not code-compliant because it isn't graspable.
What size lumber for stair stringers?
2×12 is the recommended and most common size. When you notch a stringer for the rise and run, the code wants roughly 5 inches of uncut material left behind the deepest notch. A 2×10 doesn't leave enough throat once notched, so 2×12 is the safe default. Solid (cleated) stringers avoid notching entirely.
Can deck stairs have open risers?
Yes, but only if a 4-inch sphere cannot pass through the open space between treads (IRC R311.7.5.1). For typical riser heights that means you need a partial riser back-stop or you must close the risers. Open risers look modern but are restricted for child and pet safety.
How tall does a deck stair guard need to be?
A minimum of 34 inches measured from the tread nosings (IRC R312), which is different from the 36-inch deck-level guard. Guard infill on stairs must block a 4⅜-inch sphere, and the triangular gap at the tread/riser/bottom-rail must block a 6-inch sphere. Stairs need a guard whenever they're more than 30 inches above grade.
Do deck stairs need a landing at the bottom?
Yes. IRC R311.7.6 requires a landing at the foot of the stairs at least as deep as the stair width (minimum 36 inches), on a firm and level surface — concrete, pavers, or compacted gravel. Bare soil doesn't qualify, and a single flight can't exceed 12 feet of vertical rise without an intermediate landing.
How many stringers do I need?
Spacing depends on tread material. Pressure-treated treads allow up to 16 inches on center between stringers; composite treads usually require 12 inches on center because of edge deflection under point loads. A 36–42 inch wide stair typically uses three stringers; wider stairs add a fourth. DeckMath's stair-stringer calculator spaces them for you.
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