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US Building Codes: The IRC, State by State

US residential building codes are set state by state, each adopting a different edition of the IRC with local amendments — and some states run their own codes entirely. This hub tracks what applies in your state.

Which edition applies, by state

  • Alaska Adopted
    Current
    AHFC Residential Code (2018 IRC)

    statewide minimum for 1-4 unit residential per HB 80/AHFC regulation, effective Jan 1, 2026; previously no statewide 1-2 family code (local enforcement only)

  • Alabama Adopted
    Current
    Alabama Residential Code (2015)

    statewide, effective 10/1/2016; authority transferred to Home Builders Licensure Board Oct 2024, new edition pending (not yet confirmed adopted)

  • Arkansas Adopted
    Current
    Arkansas Residential Code (2021)

    statewide (Arkansas Fire Prevention Code Vol. III), effective Jan 1, 2023

  • Arizona Local
    Current
    local adoption

    local adoption — no mandatory statewide residential code; cities/counties adopt & amend their own IRC edition

  • California Adopted
    Current
    California Residential Code (2025)

    California uses the California Residential Code (2025 CRC, based on IRC 2024), in force since 1 January 2026. Stair geometry matches the IRC, but California requires taller 42-inch (1067 mm) guards.

  • Colorado Local
    Current
    local adoption

    local adoption — no mandatory statewide residential building code; jurisdictions adopt & amend their own IRC edition (statewide energy code board sets minimum IECC only)

  • Connecticut Adopted
    Current
    2022 Connecticut State Building Code (own state code, 2021 IRC portion)

    mandatory statewide, effective Oct 1, 2022

  • Delaware Local
    Current
    local adoption

    local adoption — no mandatory statewide residential code; counties/towns adopt own IRC edition (e.g. Sussex Co. 2021, New Castle 2018)

  • Florida Adopted
    Current
    Florida Building Code, Residential (8th Edition, 2023)

    Florida uses the Florida Building Code, Residential (8th Edition, 2023, based on IRC 2021), effective 31 December 2023. Its amendments target wind and the High-Velocity Hurricane Zone, not stair…

  • Georgia Adopted
    Current
    Georgia State Minimum Standard One- and Two-Family Dwelling Code (IRC 2024 with Georgia…

    Statewide mandatory; new mandatory codes effective January 1, 2026 (2024 IRC with GA amendments)

  • Hawaii Adopted
    Current
    Hawaii State Residential Code (IRC 2021)

    State code based on 2021 IRC, effective March 6, 2022; each of the 4 counties must adopt/amend within 2 years, and the state code becomes the interim county code if a county fails to adopt

  • Iowa Local
    Current
    Iowa State Building Code residential provisions (Iowa Residential Code, based on IRC 2015)

    The Iowa State Building Code residential provisions are based on the 2015 IRC; for new one- and two-family dwellings, adoption is a LOCAL OPTION (Iowa Code Ch. 103A lets jurisdictions adopt other…

  • Idaho Adopted
    Current
    Idaho Residential Code (2020 Edition, based on IRC 2018)

    Statewide, effective January 1, 2021; adopted by state statute via Idaho Building Code Board (DOPL)

  • Illinois Local
    Current
    IRC (edition varies by jurisdiction)

    No single statewide IRC edition; local jurisdictions adopt. Public Act 103-0510 requires a statewide baseline effective 1/1/2025 — local residential codes must be at least as stringent as the IRC…

  • Indiana Adopted
    Current
    Indiana Residential Code (2020 Edition, based on IRC 2018)

    Statewide (Indiana's own state-amended residential code based on 2018 IRC), adopted by the Indiana Fire Prevention and Building Safety Commission

  • Kansas Local
    Current
    IRC (edition varies by jurisdiction)

    No statewide residential code; home-rule local adoption. Commonly adopted edition among major cities (Wichita, Overland Park, Kansas City KS) is the 2018 IRC with local amendments

  • Kentucky Adopted
    Current
    2018 Kentucky Residential Code (3rd Edition)

    Statewide mandatory; 3rd Edition effective Aug 1, 2024. NOTE: named '2018 KRC' but its model base is the 2015 IRC (with KY amendments), not the 2018 IRC.

  • Louisiana Adopted
    Current
    Louisiana State Uniform Construction Code (2021 IRC)

    Statewide mandatory for new one/two-family dwellings; 2021 IRC effective Jan 1, 2023. Enforcement applies to new construction/additions/major alterations.

  • Massachusetts Adopted
    Current
    Massachusetts Residential Code, 10th Edition (780 CMR, Ch. 51) — 2021 IRC

    Statewide mandatory; 10th Edition effective Oct 11, 2024, concurrency period with 9th Edition ended June 30, 2025 (so 10th Ed. is now the sole code).

  • Maryland Adopted
    Current
    Maryland Building Performance Standards (MBPS) — 2021 IRC

    Statewide uniform standard (MBPS, COMAR 09.12.51), 2021 IRC effective May 29, 2023; local jurisdictions required to implement/enforce by May 29, 2024 and may adopt local amendments.

  • Maine Adopted
    Current
    Maine Uniform Building and Energy Code (MUBEC) — 2021 IRC

    Statewide uniform code; updated from 2015 to 2021 I-codes effective ~Apr 7, 2025. Statewide standard, but enforcement is mandatory only in municipalities that enforce MUBEC (small towns under ~4,000…

  • Michigan Adopted
    Current
    IRC (edition contested) — 2021 Michigan Residential Code adopted but implementation…

    Statewide mandatory. 2021 Michigan Residential Code (2021 IRC base) filed May 1, 2025, effective date Aug 29, 2025 and the 2015 scope rule was rescinded effective that date; HOWEVER a July 7, 2025…

  • Minnesota Adopted
    Current
    2020 Minnesota Residential Code (Minn. Rules Ch. 1309) — 2018 IRC

    Statewide mandatory; adopts by reference the 2018 IRC (Ch. 2-10 etc.) as amended, effective Mar 31, 2020.

  • Missouri Local
    Current
    No statewide residential code; local adoption (edition varies, commonly IRC 2015-2018)

    Local adoption only — no mandatory statewide building/residential code; cities and counties adopt their own IRC edition (KC, St. Louis have local amendments)

  • Mississippi Local
    Current
    IRC 2021 (statewide minimum; adoption left to local jurisdictions)

    Local adoption; MS Building Codes Council discretionary statewide minimum = 2021 IRC, published eff. July 1, 2024; cities/counties choose from the 3 most recent council-approved editions

  • Montana Adopted
    Current
    Montana Residential Code (2021 IRC)

    Mandatory statewide; 2021 IRC incorporated by reference via ARM 24.301.154 (initial 2021 adoption eff. 2022; re-adoption eff. Sept 21, 2024)

  • North Carolina Adopted
    Current
    2018 North Carolina Residential Code (NCRC)

    Statewide own-cycle code; 2018 NCRC (based on 2015 IRC) effective Jan 1 2019 and STILL current — the 2024 NC code was delayed/postponed indefinitely (Mar/Apr 2025)

  • North Dakota Local
    Current
    North Dakota State Building Code — 2024 IRC

    Local adoption (opt-in): 2024 IBC/IRC state code effective Jan 1 2026; mandatory for state/local govt buildings & schools, and any city/county/township that chooses to enforce building codes must…

  • Nebraska Local
    Current
    Nebraska State Building Code (2018 IRC)

    State Building Code adopts 2018 IRC; codes largely enforced by local jurisdictions, but since Aug 28, 2021 the state code applies as the default where a locality has not adopted a conforming code…

  • New Hampshire Adopted
    Current
    NH State Building Code — Residential Code for One- and Two-Family Dwellings (2021 IRC)

    Mandatory statewide; 2021 IRC effective July 1, 2024. A 2024 IRC update is scheduled effective July 1, 2026 with a concurrence period (July 1-Dec 31, 2026) during which either the 2021 or 2024 edition…

  • New Jersey Adopted
    Current
    NJ Uniform Construction Code — One- and Two-Family Dwelling Subcode (2021 IRC, New Jersey…

    Mandatory statewide via UCC (N.J.A.C. 5:23-3.21); 2021 IRC NJ Edition subcode effective March 2023

  • New Mexico Adopted
    Current
    New Mexico Residential Code 2021 (NMRC)

    Statewide; 2021 NMRC (14.7.3 NMAC) in effect (phased 2023–2024)

  • Nevada Local
    Current
    No single statewide residential code; local adoption (edition varies, IRC 2018-2024)

    Local adoption — permits issued/enforced by city & county building depts (e.g. Clark Co./Las Vegas 2018 IRC, Washoe Co. 2024 IRC). State Public Works adopted 2024 IRC only for state-owned projects

  • New York Adopted
    Current
    Residential Code of New York State (own code) — 2025 RCNYS (2024 IRC) being phased in;…

    Statewide own code; 2025 RCNYS adopted (Notice of Adoption 2025-07-24, derivative of 2024 IRC), replacing 2020 RCNYS (2018 IRC); effective date not firmly confirmed. NYC runs its own construction…

  • Ohio Adopted
    Current
    2019 Residential Code of Ohio (RCO)

    Statewide code (2019 RCO, based on 2018 IRC, effective Jul 1 2019; amended eff. Mar 1 2024); enforcement of 1–3 family dwellings is at local jurisdiction option

  • Oklahoma Adopted
    Current
    Oklahoma Residential Code — 2018 IRC

    Statewide minimum code set by OUBCC; 2018 IRC (amended, eff. Sep 14 2022) in effect until Sep 14 2026, when 2024 IRC takes over. Adopted/enforced by local jurisdictions.

  • Oregon Adopted
    Current
    2023 Oregon Residential Specialty Code (ORSC)

    Statewide (no local amendments); 2023 ORSC based on 2021 IRC, effective Oct 1 2023, mandatory Apr 1 2024

  • Pennsylvania Adopted
    Current
    Pennsylvania Uniform Construction Code (UCC) — 2021 IRC

    statewide UCC; effective Jan 1, 2026 for permit applications (prior permits: 2018 IRC)

  • Rhode Island Adopted
    Current
    RI One- and Two-Family Dwelling Code SBC-2-2021

    statewide; effective Feb 1, 2022 (own named SBC-2 code, directly based on IRC)

  • South Carolina Adopted
    Current
    South Carolina Residential Code (2018)

    statewide; effective Jan 1, 2020 (2024 IRC in adoption/comment process, not yet effective)

  • South Dakota Local
    Current
    local adoption — no statewide residential (IRC) code

    local adoption; state has no mandatory statewide one/two-family dwelling code (edition varies by jurisdiction)

  • Tennessee Adopted
    Current
    Tennessee Residential Code (2018)

    statewide minimum; some local jurisdictions adopt newer (e.g. Nashville 2024, Wilson Co. 2021) or counties may opt out

  • Texas Adopted
    Current
    IRC 2012 statewide minimum; actual edition set by local jurisdiction (commonly newer)

    statewide floor only (HB 738, eff. 2022 sets 2012 IRC as municipal minimum); cities/counties adopt & amend, often 2015–2021

  • Utah Adopted
    Current
    Utah State Construction Code — 2021 IRC

    statewide; effective Jul 1, 2023 (2024 IRC not confirmed adopted; could not fully rule out a 2025 update)

  • Virginia Adopted
    Current
    2021 Virginia Residential Code (part of Virginia USBC)

    Mandatory statewide (USBC). Effective Jan 18, 2024; 2021 provisions mandatory for all new permits from Jan 18, 2025

  • Vermont Local
    Current
    No statewide residential building code for owner-occupied 1-2 family dwellings (only RBES…

    No statewide IRC-based residential code; VT Fire & Building Safety Code exempts owner-occupied single-family homes. Only statewide requirement for new residential is the Residential Building Energy…

  • Washington Adopted
    Current
    2021 Washington State Residential Code (WSRC)

    Mandatory statewide (WAC 51-51), with WA amendments. Effective March 15, 2024

  • Wisconsin Adopted
    Current
    Wisconsin Uniform Dwelling Code (UDC), SPS 320-325

    Mandatory statewide for new 1- & 2-family dwellings; administered by DSPS; code text updated monthly (current per WI Administrative Register)

  • West Virginia Adopted
    Current
    West Virginia Residential Code (2018 IRC based)

    State Building Code adopted by WV State Fire Commission; effective Aug 1, 2022. Statewide standard but enforcement requires local adoption by municipalities/counties

  • Wyoming Local
    Current
    IRC (edition not confirmed statewide) - local adoption

    local adoption

  • District of Columbia Adopted
    Current
    2017 DC Residential Code (part of 2017 DC Construction Codes)

    Mandatory (single jurisdiction). 2017 DC Construction Codes (based on 2015 I-codes) effective May 29, 2020; modernization to newer editions underway but not yet adopted as of 2026

Adoption timing changes on government timelines — entries marked Verify are being confirmed with the relevant authority.

Rules by topic

The parts of the code a chippie actually sets out — each one in plain English, with the numbers and a calculator.

Stairs

Footings & slabs

Room heights

Ramps

Wet areas

How the code works here

There is no single US building code. The rule most homes are built to is the International Residential Code (IRC) — the “I-codes” written by the ICC. But the IRC is a model code. On its own it has no force. It is just a template.

A code only becomes law when your state and/or your town adopts it — and they almost always change parts of it first. Those changes are called amendments. So the book you actually build to is the IRC as your state and town wrote it, not the plain ICC text.

Which edition is in force?

It’s a patchwork. Different places are on different editions. Many towns are still on IRC 2018 or 2015, while others have moved to 2021 or 2024. And some places don’t use the IRC at all:

  • California runs its own California Residential Code (CRC).
  • Wisconsin has its own state code.
  • New York City and Chicago run their own codes too.

The base numbers have stayed steady across the 2015–2024 editions, so the figures on the stair page below are a solid starting point. But they are a starting point, not the final word.

The first job on every job

Before you set out a single step, confirm two things for the exact spot you’re building:

  1. Which edition of the IRC (or local code) your state and town have adopted.
  2. What amendments they’ve added on top.

Your local building department is the one who signs off, so their adopted-and-amended edition is the number that counts — not the plain ICC book, and not what the next county does.

By state