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US Residential Building-Code Adoption by State

Research for the Bones inference engines (framing / electrical / plumbing / HVAC). Companion dataset: data/jurisdictions-adoption.json.

Disclaimer: Drafting aid, not engineering. Typical/approximate values — verify with the local authority having jurisdiction (AHJ). Researched 2026-08-13; adoption status changes constantly.

1. How US residential codes work (the 60-second model)

There is no national building code in the US. A private nonprofit, the International Code Council (ICC), publishes model codes on a 3-year cycle — for houses, the International Residential Code (IRC) (editions: 2015, 2018, 2021, 2024). Model codes have no legal force until a state or local government adopts them, almost always with amendments (UpCodes state pages, passim).

Adoption patterns fall into three buckets:

  1. Statewide-mandatory (majority of states): a state agency, board, or the legislature adopts one IRC edition + a state amendment package. Some forbid local amendment entirely (CT — "adopted at the state level and cannot be amended locally" per UpCodes CT; also IN, VA, NJ, OR); others let locals amend upward (CA, WA, GA, MD).
  2. Statewide code, local-option enforcement: the state defines the code but towns choose to (or are too small to) enforce it — Maine (enforcement mandatory only in municipalities >4,000 pop., UpCodes ME), Minnesota (residential enforcement optional outside the Twin Cities metro), Montana (1–2 family permits only in "certified" local jurisdictions), West Virginia (county opt-in), North Dakota, Iowa, Tennessee (local opt-out by 2/3 vote).
  3. Local adoption (~14 jurisdictions in our dataset): no statewide residential code — each city/county picks its own edition and amendments. Texas (IRC "as it existed on May 1, 2012" is the statutory municipal baseline; cities adopt newer editions by ordinance; unincorporated areas largely unregulated — Tex. Loc. Gov't Code §214.212), Missouri, Colorado ("home rule" cities/counties, UpCodes CO), Kansas ("home rule state; the responsibility for adoption and enforcement… lies with local jurisdictions", UpCodes KS), plus AZ, AK, DE, IL (until the 2025 statewide backstop), MS (opt-in/opt-out), NV, SD, VT, WV, WY.

Two states are special: Wisconsin uses its own state-written Uniform Dwelling Code (SPS 320–325) rather than the IRC (UpCodes WI) — different table numbering, different bracing rules. Florida publishes the standalone Florida Building Code — Residential (8th ed. 2023, 2021 IRC base, eff. 2023-12-31, FBC-R 8th) with hurricane provisions woven throughout and extra-strict HVHZ rules in Miami-Dade and Broward.

2. Does framing practice change by state or by zip code?

Both, in different ways — and this is the key architectural insight for Bones:

2a. The rulebook (code edition + amendments) is mostly chosen at the state level

37 of 51 jurisdictions in our dataset have a statewide-adopted residential code. So "which IRC edition and which amendment package" is primarily a state-level lookup. The 14 local-adoption states (TX, MO, CO, KS, AZ, AK, DE, IL, MS, NV, SD, VT, WV, WY) need a city/county-level lookup — but even there, jurisdictions pick from the same small menu of IRC editions (2012–2024), so a representative default per state (with a "verify locally" flag) is a sound fallback.

Prescriptive framing between IRC editions 2015→2024 is evolutionary, not revolutionary: span tables shifted slightly with updated lumber design values (notably the 2013 Southern Pine downgrades), wall-bracing and deck provisions got refined, and wind maps moved to newer ASCE 7 editions. A framing inference engine keyed to "generic modern IRC" is a reasonable approximation across editions — flag, don't fork, per edition.

2b. The numbers you plug into the rulebook vary by county/city — sometimes by zip

Every IRC-family code has a Table R301.2(1) "Climatic and Geographic Design Criteria" that the local jurisdiction fills in. These locally-determined values are what actually change framing outputs within a state:

  • Ground snow load (Psf) — drives rafter/ridge sizing. Varies enormously within states (CO front range ~30 psf vs mountain towns 75–150+; UT and MT publish their own elevation-based snow studies replacing map values).
  • Ultimate design wind speed (Mph) — drives wall bracing, sheathing nailing, uplift connectors. Coastal counties in FL/TX/LA/NC/SC sit in 140–180 mph zones with wind-borne-debris opening protection; inland ~105–115 mph. Texas coastal counties additionally have the TDI/TWIA windstorm certification regime (2024-IRC-based standard eff. 2026-04-01, UpCodes TX).
  • Seismic Design Category — SDC D0–E (much of CA, western WA/OR, Wasatch Front UT, Charleston SC, New Madrid MO/TN/AR) restricts prescriptive framing and forces engineered lateral design; SDC A–B (most of the east/midwest) doesn't.
  • Frost line depth (In) — sets footing depth: ~12 in in the Gulf South, 30–42 in mid-Atlantic/midwest, 48–60+ in MN/ND/ME/AK. County or municipal amendment territory.
  • Weathering, termite exposure, ice-barrier underlayment, flood zones — same table, same local variation.

So: adoption is (mostly) state; loads are local. A zip/county resolver for climatic values matters more for framing correctness than tracking every local amendment. FEMA's Building Code Adoption Tracking (BCAT) tracks this at the community level (fema.gov blocks automated fetch; portal: fema.gov/emergency-managers/risk-management/building-science/bcat).

2c. Recommended two-layer model for Bones

  1. Layer 1 — jurisdiction/adoption (state key, this dataset): IRC base edition, amendment flavor, special regimes (HVHZ, WUI, energy code, windstorm).
  2. Layer 2 — site design values (county/lat-long key, separate dataset): snow, wind, seismic, frost, termite. Source from ASCE 7 Hazard Tool / ATC hazard maps and state amendment tables, not from the adoption layer.

3. State-by-state highlights (verified 2026-08-13)

Editions below were confirmed against UpCodes adoption records (which mirror ICC Digital Codes) and state sources; full detail incl. effective dates is in the JSON.

On the 2024 IRC already (6): GA (eff. 2026-01-01, skipped 2021 — UpCodes GA), NY (2025 RCNYS eff. 2025-12-31 — UpCodes NY), CA (2025 CRC, Title 24 Part 2.5, eff. 2026-01-01 — CA BSC; CRC base is the 2024 IRC), IA (eff. 2025-09-10), ND (eff. 2026-01-01), NH (eff. 2026-07-01). MD boards began adopting 2024 editions Nov 2025 (MBPS-wide status: verify). MS designated the 2024 IRC (eff. 2025-01-01) for opt-in jurisdictions.

On the 2021 IRC (largest cohort): AR, CT, FL (FBC-R 8th), LA, ME (MUBEC eff. 2025-04-07), MD (MBPS eff. 2023-05-29), MA (780 CMR 10th ed. eff. 2024-10-11), MI (2021 MRC eff. 2025-08-29 — recent!), MT, NJ, NM, OR (2023 ORSC), PA (eff. 2026-01-01 — just switched from 2018), RI (eff. 2025-12-01), SC, UT, VA, WA, and CO/HI as representative bases.

On the 2018 IRC: AK (AHFC), ID (2020 Idaho code), IN (2020 Indiana code), MN (2020 MN code), NE, OK (eff. 2022-09-14), TN, WV, and AZ/DE/KS/MO/WY as representative local bases.

Still on the 2015 IRC: AL (2015 Alabama Residential Code, eff. 2016 — UpCodes AL), KY (the "2018 Kentucky Residential Code" is named 2018 but based on the 2015 IRC — trap!), NC (2018 NCRC = 2015 IRC base; the 2024 NCRC (2021 base) has been postponed repeatedly by session law — UpCodes NC), DC (2017 DC Codes = 2015 I-codes, eff. 2020).

No IRC at all: WI (state-written UDC), VT (no state residential code for detached 1–2 family; only RBES energy standards statewide).

Special regimes an inference engine should know about

  • FL HVHZ (Miami-Dade/Broward): impact protection, enhanced uplift, product approval.
  • CA Chapter 7A / WUI: ignition-resistant exterior assemblies in Fire Hazard Severity Zones; CO stood up a Wildfire Resiliency Code Board (2025) for mapped WUI areas.
  • TX coastal windstorm (TDI/TWIA) and industrialized housing (2021 IRC, eff. 2024-07-01) run on their own IRC editions independent of city codes.
  • Energy codes often ride a different edition than the building code (e.g., WA's state-written energy code; IL statewide energy + plumbing codes despite local building adoption; TN's reduced energy requirements).
  • NYC has its own construction codes, separate from the NYS Uniform Code.

4. What is approximate in the dataset (read before trusting)

  • Local-adoption states: ircBase is a representative metro value, not a guarantee (flagged in each note). TX/CO/MO especially — the same house design may face 2015 IRC in one suburb and 2024 in the next.
  • Alabama: UpCodes still shows the 2015 base as current; the Energy & Residential Codes Board has been reviewing newer editions — verify.
  • Hawaii: state adopted 2018 (and recorded a 2021 adoption in 2022), but county codes control and lag; Honolulu practices on the 2018 base.
  • Maryland: MBPS 2021 confirmed; a 2024 MBPS update appeared imminent (plumbing board already on 2024 IRC, eff. 2025-11-24).
  • North Carolina: the 2024 NCRC (2021 base) is adopted-but-postponed; legislative delays (S.L. 2024-57, S.L. 2025-2) make its effective date volatile.
  • Illinois: the 2025 statewide backstop exists (CDB) but CDB's designated editions weren't verifiable from the page — 2021 assumed.
  • Effective-date cliffs around now: PA (2026-01-01), GA (2026-01-01), NH (2026-07-01), NY (2025-12-31), ND (2026-01-01), NJ (2024-base subcode expected 2026-08-17). Projects permitted under transition provisions may legally use the prior edition.
  • Enforcement ≠ adoption: many "state" rows (ME, MN, MT, IA, ND, TN, OK, AL) have thin-to-zero rural enforcement; the code still nominally applies.

5. Sources

Primary/authoritative consulted: Texas Loc. Gov't Code §214.212 (texas.public.law mirror; statutes.capitol.texas.gov is JS-only), California BSC, Oregon BCD adopted codes, WA State Building Code Council, Illinois CDB, Ohio Admin. Code 4101:8, MN DLI codes. Per-state adoption records: UpCodes state pages and adoption viewers (full URL list in the JSON sources array) — UpCodes mirrors official adoption filings incl. links to ICC Digital Codes and state registers (e.g., Michigan Register No. 10-2025 for the 2021 MRC, eff. 2025-08-29). ICC's own adoption map (iccsafe.org/advocacy/code-adoption-map/) and FEMA BCAT block automated access; they are the canonical cross-checks for a human reviewer.