What is the International Residential Code, and which edition applies to my house?
Published · Updated · By Sai Nath
The International Residential Code (IRC) is the International Code Council's model code for one- and two-family houses and townhouses up to three stories. It is revised every three years; the 2021 and 2024 editions are both in use. It binds only where a state or city adopts it, often with amendments, so your building department decides.
What is the IRC?
The International Residential Code is a model building code written by the International Code Council (ICC). Section R101.2 sets its scope: detached one- and two-family dwellings and townhouses no more than three stories above grade plane, each with its own means of egress, and their accessory structures. One book covers structure, stairs, guards, decks, energy and the services. The ICC says the IRC is in use or adopted in 49 states, the District of Columbia, Guam, Puerto Rico and the US Virgin Islands, and both current editions can be read free online, read-only, at codes.iccsafe.org.
Which edition: 2021 or 2024?
The ICC revises the IRC every three years. The 2021 and 2024 editions are the ones being adopted now; some places still build to 2018 or older. Most house figures did not change in 2024, but Chapter 3 was renumbered, so the same rule has a different section number in each edition.
| Rule | 2021 IRC | 2024 IRC | Guide |
|---|---|---|---|
| Stairways: risers, treads, headroom, landings | R311.7 | R318.7 | Stairs |
| Handrails | R311.7.8 | R318.7.8 and R320 | Stairs |
| Guards: when, how high, the 4 in sphere | R312.1 | R321.1 | Guards |
| Window fall protection | R312.2 | R321.2 | Guards |
| Decks | R507 | R507 | Decks |
| Live loads (decks 40 psf, guards 200 lb) | Table R301.5 | Table R301.5 | Decks |
| Work exempt from a permit | R105.2 | R105.2 | Below |
What changed on site from 2021 to 2024:
- Landings: new exceptions for a door at the top of an interior stair, a garage top landing, short exterior stairs and three-riser deck stairs (R318.7.6).
- Nosings: the 3/8 in limit on nosing differences now includes the landing at the top, and on open-riser stairs the nosing may project more than 1 1/4 in (R318.7.5.3).
- Handrails: they run from above the nosing of the top landing to above the lowest nosing, and a return may leave no more than a 1/4 in gap to the wall (R320.5).
- Decks: the beam table is read by actual joist span and overhang, and new rules cover ledger flashing and the water-resistive barrier behind it (R507.5, R507.9.1.5 to R507.9.1.8).
Who decides which rules apply to my house?
The IRC has no force until a state, county or city adopts it by law, and most adopt it with amendments. Chapter 1 is written to be filled in by the jurisdiction, and so is Table R301.2: the frost line depth, snow load, wind speed and termite risk for your area come from your building department, not from the ICC. Three states show how far apart places are:
- Oklahoma adopted the 2024 IRC as its statewide minimum code from 14 September 2026, with amendments. One lets the top and bottom riser of each flight differ from the rest by up to 3/4 in (19 mm), where the model code allows 3/8 in.
- Washington adopts the 2021 IRC with state amendments (chapter 51-51 WAC), in force since 16 March 2024.
- North Carolina builds to its own 2018 North Carolina Residential Code, which the state fire marshal's office lists as currently effective. It allows stair risers up to 8 1/4 in, and a flight to rise 12 ft 3 in between landings.
Cities and counties can add amendments where state law lets them. The building department that issues your permit can tell you the edition, the amendments and the local values in Table R301.2. The model code exempts some work from a permit (R105.2), for example a free-standing deck of 200 sq ft or less, no more than 30 in above grade, that doesn't serve the required exit door. Jurisdictions often change that list, so ask before you build.
The house numbers people ask about
| What | Figure | 2021 IRC | 2024 IRC |
|---|---|---|---|
| Stair riser | 7 3/4 in (196 mm) at most | R311.7.5.1 | R318.7.5.1 |
| Stair tread | 10 in (254 mm) at least | R311.7.5.2 | R318.7.5.2 |
| Headroom over a stair | 6 ft 8 in (2032 mm) | R311.7.2 | R318.7.2 |
| Handrail | 34 to 38 in (864 to 965 mm) high, on flights of four or more risers | R311.7.8 | R318.7.8, R320.2 |
| When a guard is needed | More than 30 in (762 mm) above the floor or grade within 36 in (914 mm) of the edge | R312.1.1 | R321.1.1 |
| Guard height | 36 in (914 mm); 34 in (864 mm) on stairs | R312.1.2 | R321.1.2 |
| Openings in a guard | No 4 in (102 mm) sphere through; 4 3/8 in (111 mm) on stair sides | R312.1.3 | R321.1.3 |
| Deck footing depth | At least 12 in (305 mm) below undisturbed ground | R507.3.2 | R507.3.2 |
| Deck joist span | Southern pine 2x10 at 16 in centres: 14 ft 0 in (4267 mm) | Table R507.6 | Table R507.6 |
| Deck ledger | 2x8 at least | R507.9.1.1 | R507.9.1.1 |
How to use these pages
Each topic page gives the figure, its section in both editions, a worked example and what MeisterCalc does with it. The figures are the model code's: check the edition and the amendments with your local building department, and build to your permit drawings. Neither these pages nor the app make work pass inspection.
MeisterCalc works in feet, inches and sixteenths (Settings ▸ Units ▸ Default units ▸ Imperial (ft/in)). Stairs and Concrete are free; Baluster Spacing, Stud Counter and Running Measurements come with Pro. The free stair calculator checks a stair against the IRC riser, tread and headroom, and the free concrete calculator gives cubic yards and 40, 60 or 80 lb bags.
United States rules, topic by topic
- What are the IRC stair rules for risers, treads and headroom?
- What is the baluster spacing code for decks and stairs?
- What does the building code say about deck joist spans, posts and footings?
Sources
Checked on 2 November 2026. These pages explain the rules; the code itself, your plans and your council, building consent authority, building control body or certifier decide what a job needs.
- ICC, The International Residential Code: what the IRC covers, the three-year cycle, in use or adopted in 49 states, DC, Guam, Puerto Rico and the US Virgin Islands (checked 1 November 2026)
- 2024 IRC, Chapter 1 Scope and Administration (ICC): R101.2 scope; R105.2 work exempt from permit, item 10 decks (the same in the 2021 IRC) (checked 1 November 2026)
- 2021 IRC, Chapter 3 Building Planning (ICC): Table R301.2 values filled in by the jurisdiction, Table R301.5, R311.7 stairways, R312 guards (checked 1 November 2026)
- 2024 IRC, Chapter 3 Building Planning (ICC): R318.7 stairways, R320 handrails, R321 guards: the 2024 numbering (checked 1 November 2026)
- 2024 IRC, Chapter 5 Floors (ICC): R507 decks, compared line by line with the 2021 edition (checked 1 November 2026)
- Oklahoma Uniform Building Code Commission, IRC 2024 permanent rule (PDF): 2024 IRC as the statewide minimum code from 14 September 2026; amendment to R318.7.5.1 (top and bottom riser may vary by 3/4 in) (checked 2 November 2026)
- Washington, WAC 51-51-003: adopts the 2021 IRC; history note gives effective 16 March 2024 (checked 1 November 2026)
- NC Office of State Fire Marshal, codes current and past: the 2018 North Carolina Residential Code is currently effective (checked 1 November 2026)
- NC Office of State Fire Marshal, interpretation of 2018 NCRC R311.7.5.1, 17 August 2023 (PDF): quotes R311.7.5.1 (risers up to 8 1/4 in) and R311.7.6 (12 ft 3 in between landings) (checked 1 November 2026)
Do the maths in MeisterCalc
MeisterCalc does the arithmetic behind these rules on an Android phone, with no signal needed: Stairs, Concrete and Check Square are free, and the other calculators come with Pro. It runs on Android 7.0 or later.