Published
Which building-code editions actually apply to a St. Anthony permit today.
The state decides the edition — and it is not always the newest one
Ask two people which building code applies to a new house in St. Anthony and you will usually hear two answers, because the desks print different lists — that story is already on this site. But underneath both desks sits a single state decision, made by rule: IDAPA 24.39.30, the Idaho Building Code Board’s Rules of Building Safety, which adopts the specific editions of the building codes that Idaho enforces. The rule in force is marked effective 7-1-24, re-read from the state’s published PDF on 11 September 2026. Its adopting sentence runs, in full: “Pursuant to Sections 39-4109 and 39-4109A, Idaho Code, the Board adopts the following international codes with identified amendments.”
Two things in that sentence do a lot of work. The board adopts — not the city, not the county — so the edition is the same on both sides of the city limits line. And it adopts codes “with identified amendments” — the books the county and the city enforce are not the model publishers’ books. They are the Idaho versions, and the amendments are printed in the same rule.
The one that matters to a house is the residential code, and the rule’s own words are worth reading:
“International Residential Code, 2018 Edition. Parts I, II, III, and IX of the 2018 Edition for one (1)- and two (2)- family dwellings…”
— IDAPA 24.39.30, section 600.03, Idaho Building Code Board. Effective 7-1-24. Retrieved 11 September 2026
That is the “Idaho Residential Code” a permit packet refers to: the 2018 IRC, Parts I through III and IX, with the state’s amendments layered on top of it.
Every edition the rule adopts
The rule’s section 600 adopts six bodies of code in one list. Here is that list as one table — which book, which edition, and what Idaho’s rule does to it:
| Code book | Edition in the state rule | What Idaho’s rule does to it |
|---|---|---|
| International Building Code | 2018 (accessibility appendices included) | Amended — occupancy classifications, plumbing-fixture footnotes, relocatable-buildings section and more reworked |
| International Building Code, mass-timber provisions only | 2021 | A defined slice of the newer edition — definitions, sections, tables and standards for tall mass-timber construction — grafted onto the 2018 book |
| International Residential Code | 2018, Parts I, II, III and IX, for one- and two-family dwellings | Heavily amended — see the list below |
| International Existing Building Code | 2018 | Adopted as-is — the rule lists no amendments to it |
| International Energy Conservation Code — commercial provisions | 2018 | Amended — exemptions added for equipment-only buildings, accessory utility structures, well and pump buildings |
| International Energy Conservation Code — residential provisions | 2018 | Amended — definitions, climate-zone requirement rows replaced, a visual-inspection option, and a log-home path |
So the short answer to “which edition applies today?” is: the 2018 family, with one 2021 guest. There is no 2021 IRC in Idaho, no 2024 anything — the only 2021 content in the rule is that mass-timber slice of the IBC, and tall mass-timber is not a house.
The residential amendments a house actually feels
The IRC amendments are where the Idaho version of the code visibly parts company with the model book. Each item below is the rule’s own instruction, section by section:
- Sprinklers in houses: deleted. The rule’s instruction for section R313.2 — the model code’s automatic fire-sprinkler requirement for one- and two-family dwellings — reads, in full, “Delete.” Townhouse sprinklers (R313.1) are amended rather than deleted, with an exception built around rated walls between units.
- Whole-house mechanical ventilation: written in. Section R303.4 is deleted and replaced with a sentence requiring dwelling units to have whole-house mechanical ventilation.
- Footing tables: replaced wholesale. The model code’s minimum footing-width tables are deleted, and the rule substitutes its own Table R403.1 with minimum sizes set from soil bearing value and story count.
- Wall bracing: an alternative route. Section R602.10 is replaced to allow the most current edition of APA System Report SR-102 as an alternate bracing method.
- The permit exemptions: nudged. One exemption’s measurement is amended from 24 inches to four feet, and flag poles are added to the work that needs no permit at all.
- Detached-garage separation: re-tabled. The dwelling-garage separation table is deleted and replaced with the rule’s own.
None of this is secret — it is all in the rule’s section 600.03, pages anyone can read. But almost nobody reads it, which is how a plan drawn straight out of a model-code summary can arrive at a counter already short of what the Idaho version asks for.
What this rule is not
Three honest limits, so the page does not promise more than the rule delivers. First, this rule covers the international building-code family above — plumbing, electrical and mechanical editions live in other state rules, and the city’s own application prints that side of the list; the mismatch between the two desks’ printed lists is the story of the two code books. Second, this rule is not zoning — setbacks, uses and the county’s questionnaire are a different law entirely, mapped in the eleven questions the county asks. Third, the rule amending the code is a moving document: the board proposes, the legislature approves, and the PDF on the state’s site is the current word — the copy behind this page is dated 11 September 2026.
Energy is the special case. The 2018 IECC editions in this rule are the same books the energy chapter of state law locks in place — and locks against any local addition: what neither desk can add on top of the energy code is the previous day’s story on this site. And when your packet is finally assembled, the completeness clock that governs the answer is not this rule’s — it is the 2025 statute behind the ten-business-day review law.
Check the edition before anyone draws anything
- Open the rule itself — search “IDAPA 24.39.30” — and read section 600’s list before you read any blog summary, including this one.
- Confirm the effective date printed beside the text you rely on; the copy cited here is the 7-1-24 edition, retrieved 11 September 2026.
- Hand your designer the two words that matter: 2018 IRC, as amended by Idaho — not the plain model book.
- Ask directly how the state’s amendments land on your plan — ventilation, footings, bracing, garage separation are the usual four.
- If a plan or product sheet cites a newer edition’s section number, ask which Idaho rule adopted it — in the 7-1-24 rule, only the mass-timber slice of 2021 is in force.
- Keep the rule’s PDF with your permit file; a printed edition citation settles arguments a memory cannot.
- Then call (208) 656-1745 with the one question your build actually turns on — which edition, which amendment, which desk.
Common questions
What building code edition applies to a new house in St. Anthony?
The International Residential Code, 2018 Edition - Parts I, II, III and IX, for one- and two-family dwellings - as amended by Idaho's building code board rule IDAPA 24.39.30, effective 7-1-24. That model code plus the state's amendments together are the Idaho Residential Code.
Has Idaho adopted the 2021 or 2024 building codes?
No. The board's rule adopts the 2018 IBC, IRC, IEBC and IECC. The only 2021 content in force is a defined set of mass-timber provisions from the 2021 International Building Code, grafted onto the 2018 edition.
Are fire sprinklers required in a new Idaho house?
Not by the residential code Idaho adopts: the rule's instruction for section R313.2 - the model IRC's automatic sprinkler requirement for one- and two-family dwellings - is 'Delete.' Townhouse requirements are amended separately, with an exception tied to rated walls between units.
What is the 'Idaho Residential Code' my permit mentions?
The 2018 International Residential Code with the amendments Idaho's board adopted in IDAPA 24.39.30 - deletions, replacements and additions that change ventilation, footings, bracing, garage separation and more.
Which code applies to a renovation or addition?
The 2018 International Existing Building Code, adopted as-is in the same rule, alongside the 2018 IRC for dwellings. Work on an existing house can fall under either depending on scope.
Where do the plumbing, electrical and mechanical editions come from?
Other state rules, not this one. IDAPA 24.39.30 adopts the international building-code family only; the trade codes your packet lists are adopted separately, and the two desks around St. Anthony print different versions of that side of the list.
Is the energy code in this rule the same everywhere in Idaho?
Yes. The rule adopts the 2018 IECC commercial and residential provisions with the state's amendments, and Idaho Code 39-9701 preempts any local energy requirement that differs from or goes beyond them.
Can the city or the county adopt a newer code edition locally?
Not for these code families. The board adopts the editions by rule under Idaho Code sections 39-4109 and 39-4109A; local governments enforce what the state adopted - and on energy, state law bars them from adding anything beyond it.
Where can I read Idaho's amendments myself?
In the rule itself: IDAPA 24.39.30, published as a PDF at adminrules.idaho.gov - section 600 lists every adopted edition, and sections 600.01 through 600.06 print each amendment, code section by code section.