IRC Stairs, Guards, and Handrails
Summary
The IRC sets the width, riser and tread dimensions, headroom, and landings of residential stairs, requires graspable handrails on stairs with four or more risers, and requires guards at open-sided surfaces more than 30 in. above the floor or grade. Small dimensional errors in a stair show up in inspection and injury claims, so fix riser and tread dimensions and rail details in the early sections.
Cols
Scope
- Cites the 2024 IRC, Sections R318 (means of egress, stairways, and ramps), R320 (handrails), and R321 (guards and window fall protection). Always verify the adopted code edition and local amendments for the project jurisdiction
- Applies to stairs within and serving dwellings, porches, and decks; stairs to nonhabitable attics and crawl spaces are excepted
- Egress doors and landings at doors are in Section R318 and are covered briefly here
- Commercial and multifamily stairs follow the IBC egress provisions
Terminology
- Riser: vertical face of a stair step, or its height
- Tread: horizontal surface of a step, or its depth
- Nosing: front edge of a tread that projects past the riser
- Walkline: line 12 in. from the inside of a turn, along which tread depth is measured on winders
- Winder: tapered tread in a turn
- Landing: platform at the top, bottom, or between flights
- Headroom: clear vertical height above the stair, measured from the nosing line
- Handrail: graspable rail at the side of a stair or ramp
- Guard: barrier at an open-sided walking surface that prevents falling
- Baluster: vertical infill member in a guard
- Spiral stair: stair winding around a central column
- Window opening control device: hardware that limits how far a window opens
Requirements
Stairs
- IRC 2024, Section R318.7.1: clear width at least 36 in. above handrail height; 31-1/2 in. at and below handrail height with a handrail on one side, 27 in. with handrails on both sides
- IRC 2024, Section R318.7.2: headroom at least 6 ft 8 in., measured vertically from the sloped line of the nosings or from the landing surface; a floor opening above may project up to 4-3/4 in. into the headroom
- IRC 2024, Section R318.7.3: a flight has a maximum vertical rise of 12 ft 7 in. between floor levels or landings
- IRC 2024, Section R318.7.5.1: risers at most 7-3/4 in.; variation within a flight at most 3/8 in.; at open risers, openings more than 30 in. above the floor below do not pass a 4 in. sphere
- IRC 2024, Section R318.7.5.2: treads at least 10 in. deep; variation within a flight at most 3/8 in.
- IRC 2024, Section R318.7.5.2.1: winders are at least 10 in. at the walkline and at least 6 in. at any point within the clear width
- IRC 2024, Section R318.7.5.3: nosing radius at most 9/16 in. or bevel at most 1/2 in.; projection 3/4 in. to 1-1/4 in.; no nosing needed where the tread is at least 11 in. deep
- IRC 2024, Section R318.7.6: a landing at the top and bottom of each flight at least as wide as the flight and at least 36 in. deep in a straight run, with exceptions at doors, garages, and exterior stairs of two risers or fewer
- IRC 2024, Section R318.7.7: walking surface slope at most 1:48 (2 percent); 1:20 (5 percent) where a landing must drain
- IRC 2024, Section R318.7.11.1: spiral stairs have a clear width of at least 26 in. at and below the handrail, a walkline radius of at most 24-1/2 in., a tread depth of at least 6-3/4 in. at the walkline, a rise of at most 9-1/2 in., and headroom of at least 6 ft 6 in.
- IRC 2024, Sections R318.7.12 and R318.7.13: alternating tread devices and ship's ladders are not egress elements, except in lofts and similar areas of 200 sq ft or less; clear width at least 20 in.
Egress doors, hallways, and ramps
- IRC 2024, Section R318.2: at least one side-hinged egress door per dwelling unit with a clear width of at least 32 in. and clear height of at least 78 in., openable from inside without a key or special knowledge
- IRC 2024, Section R318.3: a landing or floor on each side of exterior doors, at least as wide as the door and 36 in. deep, sloped at most 1/4 in. per foot; at the required egress door, the floor is no more than 1-1/2 in. below the top of the threshold
- IRC 2024, Section R318.6: hallways at least 3 ft wide
- IRC 2024, Section R318.8: ramps serving the required egress door have a slope of at most 1:12; other ramps at most 1:8; landings are at least 36 in. deep at top, bottom, and turns
Handrails
- IRC 2024, Section R318.7.8: handrails on at least one side of each flight with four or more risers
- IRC 2024, Section R320.2: handrail height is 34 in. to 38 in. measured vertically from the sloped plane of the tread nosings or the ramp surface
- IRC 2024, Section R320.3: handrails project at most 4-1/2 in. into the stair width (6-1/2 in. where nosings or passing flights reduce clearance)
- IRC 2024, Section R320.4: at least 1-1/2 in. between a handrail and an adjacent wall
- IRC 2024, Section R320.5: continuous for the full length of the flight, with ends returning to the wall, guard, or walking surface, with a gap of at most 1/4 in. to the wall
- IRC 2024, Section R320.6: Type I grip is circular with an outside diameter of 1-1/4 in. to 2 in., or non-circular with a perimeter of 4 in. to 6-1/4 in. and a cross section of at most 2-1/4 in.; Type II has a perimeter over 6-1/4 in. with finger recesses
Guards
- IRC 2024, Section R321.1.1: guards are required at open-sided walking surfaces, including stairs, ramps, and landings, where the drop to the floor or grade below is more than 30 in. within 36 in. horizontally of the open edge
- IRC 2024, Section R321.1.2: guards are at least 36 in. high above the walking surface, and at least 34 in. above the nosing line on stairs; where the guard top is also the handrail it is 34 in. to 38 in.
- IRC 2024, Section R321.1.3: openings do not pass a 4 in. sphere; the triangle formed by the riser, tread, and bottom rail does not pass a 6 in. sphere; guards on the open side of stairs do not pass a 4-3/8 in. sphere
- IRC 2024, Section R321.2.1: in dwelling units, a window with a clear opening bottom less than 24 in. above the floor and more than 72 in. above the grade or surface below either does not pass a 4 in. sphere when fully open or has a window opening control device (ASTM F2090)
Worked examples
Stair layout
Floor-to-floor height is 9 ft 0 in. (108 in.).
| Step | Calculation | Result |
|---|---|---|
| Trial risers | 108 ÷ 14 | 7.71 in., within 7-3/4 in. maximum |
| Number of treads | 14 risers − 1 | 13 treads |
| Run at 10 in. tread | 13 × 10 | 130 in. (10 ft 10 in.) |
| Vertical rise | 108 in. | Under 12 ft 7 in.; no intermediate landing required by rise |
| Headroom check | 6 ft 8 in. minimum | Headroom measured at the nosing line above the stair |
Deck guard
A deck surface is 36 in. above grade.
| Step | Check | Result |
|---|---|---|
| Guard needed | 36 in. is more than 30 in. | Yes |
| Guard height | 36 in. minimum | Rail top at 36 in. or higher |
| Balusters | 4 in. sphere | Spaces under 4 in. clear |
| Stair side | 34 in. above nosing line; 4-3/8 in. sphere | Stair guard with the lower sphere limit |
Window fall protection
An upstairs bedroom window sill is 18 in. above the floor and 14 ft above grade.
| Step | Check | Result |
|---|---|---|
| Sill under 24 in. | 18 in. | Yes |
| Opening above 72 in. from grade | 14 ft | Yes |
| Protection | 4 in. sphere limit or ASTM F2090 device | Required; the device must not shrink the escape opening below the minimum once released |
Coordination
- Structure: stair openings and landings need framing; guard posts at decks and balconies need blocking and edge framing for guard loads
- Millwork and stair details: riser and tread variation limits (3/8 in.) require tight dimension control, including finish floor thickness at the top and bottom
- Lighting: stairs need 1 footcandle at treads and landings and switches at each floor for six or more risers
- Window selection: low sills on upper floors drive window opening control devices
- Decks and exterior stairs: stringers, landings, and attachment use the deck provisions in Chapter 5
Common issues
- Uneven risers: finish floors added at the top or bottom change one riser by more than 3/8 in.
- Shallow landings at doors: a door that swings over a stair needs the landing
- Handrail grip: flat or square rails larger than the permitted perimeters fail
- Balusters spaced for the room but not the triangle: the triangle limit is 6 in., the stair side is 4-3/8 in.
- Open risers on stairs over 30 in.: the 4 in. sphere limit applies
- Window sills low upstairs: both the sill height and height above grade trigger protection
Standards
- ASTM F2090: window opening control devices with emergency escape release
- IRC Section R507.2.2: exterior plastic composite handrails and guards
Sources
- GoCodebook: 2025 California Residential Code, Section R318 means of egress (based on the 2024 IRC), https://gocodebook.com/library/us/ca/ca-residential-code/chapter-3-building-planning/section-r318-means-of-egress
- GoCodebook: 2025 California Residential Code, Section R320 handrails, https://gocodebook.com/library/us/ca/ca-residential-code/chapter-3-building-planning/section-r320-handrails
- GoCodebook: 2025 California Residential Code, Section R321 guards and window fall protection, https://gocodebook.com/library/us/ca/ca-residential-code/chapter-3-building-planning/section-r321-guards-and-window-fall-protection
- Building Code Forum: 2024 IRC guard height discussion, https://www.thebuildingcodeforum.com/forum/goto/post?id=318658