Idaho

Statewide summary — confirm with your building department before designing

No value on this row was changed by this audit, but ground snow load is not usable as a single number. The stored 30 psf sits between Boise, which adopts a 20 psf ground snow load, and Idaho Falls, which computes 47 psf at its elevation; central Idaho mountain communities design for well over 100 psf. Any Idaho project should use the University of Idaho ground snow load study values as adopted by the local jurisdiction. Seismic design category C is a defensible typical value: Boise adopts C and Coeur d Alene computes to C, but Idaho Falls adopts D, and Pocatello, Rexburg, McCall and the Challis area in the central Idaho seismic belt all compute to D for Site Class D and Risk Category II. Eastern and central Idaho projects should confirm locally. Frost depth of 36 inches is conservative relative to the two largest cities, since Boise adopts 24 inches and Idaho Falls 30 inches, and may still be shallow at high elevation. The 110 mph wind speed is on the ASCE 7 ultimate scale; Idaho Falls publishes 115 mph ultimate and 90 mph nominal for the same location, which shows how far apart the two conventions are. Termite risk of slight corresponds to the compound slight to moderate band of the IRC map, which is the band Boise adopts. SNOW LOAD AUDIT 2026-08-12 (physical design data pass). Minimum and maximum both left NULL, because Idaho publishes no statewide ground snow load. This is a proven absence, read out of the adopted instrument, not an assumption. Idaho does have a mandatory statewide code, and this audit read it. The Idaho Building Code Board adopts building codes through IDAPA 24.39.30, Rules of Building Safety, which is the successor to the older IDAPA 07.03.01 citation. Under Idaho Code 39-4109 and 39-4109A the Board adopts the 2021 International Building Code with a short list of Idaho amendments, the mass timber provisions of the 2021 IBC, and the 2018 International Residential Code, Parts I, II, III and IX, for one and two family dwellings, again with a short list of Idaho amendments. The word snow does not appear anywhere in that rule. The Idaho amendments to the IRC change the scope exception in R101.2, change a permit exemption threshold and add flag poles in R105.2, delete Section R301.2.1.2 on protection of openings, and replace Table R302.1(1) on exterior walls. Not one of them fills in Table R301.2(1), the climatic and geographic design criteria table, and none of them sets a ground snow load, a wind speed, a seismic design category or a frost line depth. Under the code Idaho has adopted, those cells are for the authority having jurisdiction to fill in. Idaho Code 39-4107 (powers and duties), 39-4109 (application of codes) and 39-4116 were also read in full and contain no snow load provision. Silent-failure check: the official PDF from adminrules.idaho.gov has a healthy text layer, over five hundred lines of extractable text including the full amendment lists and a rendered fire-separation table, so the nil result for the word snow is a genuine absence rather than a broken extraction. On the University of Idaho study. Ground Snow Loads for Idaho, 2015 Edition, hosted by the University of Idaho Library, is the reference Idaho jurisdictions commonly use, and it is the natural counterpart to Utah's USU study. It is not in the same legal position. This audit looked specifically for an adoption by reference and found none: it is not cited in IDAPA 24.39.30 and not cited in Idaho Code Title 39 Chapter 41. Unlike Utah, where the statute names its university study and its web address, Idaho leaves the choice to the local building official. The study is therefore a university publication and not a state-adopted source, and no number was taken from it. The four existing values were not changed and none of them can be sourced to an Idaho state instrument. Ground snow load 30 psf, ultimate wind speed 110 mph, seismic design category C and frost depth 36 inches all remain as previously recorded, with the local counterexamples already noted above still standing: Boise adopts a 20 psf ground snow load and a 24 inch frost depth and seismic category C, Idaho Falls computes 47 psf and adopts 30 inches and category D, and the central Idaho mountain communities design well above 100 psf. Look up the adopted design criteria of your jurisdiction; Idaho gives you nothing statewide to fall back on for snow.