Idaho Ground Snow Load by County and City

Idaho sets no ground snow load at state level, so every figure comes from a county or city building department. Six figures from Idaho counties and cities are set out below, each with the ordinance or code amendment it was printed in. 19 states work this way, which is why a search for one Idaho figure comes back with several different answers from several different pages, all of them correct for the place they were written for. six Idaho figures, running from 15 psf at Twin Falls to 70 lbs per sq ft at Hayden, North of Miles Avenue, every one of them quoted from the document it was printed in. Nationally 235 figures were read across 33 states.

The city or county building department: each jurisdiction sets and publishes its own figure. In its own words: “The design snow loads for roofs shall be determined using factors and methodology contained in the publication, Ground and Roof Snow Loads For Idaho by the University of Idaho, Moscow, ID 1986 and shall be site specific.”

Part of Idaho is a case study area, meaning the published document expressly declines to give those places a figure and sends the designer back to the local building department for one. 16 states carry a rule like this, and it is the commonest reason a search for a single number comes back empty. The rule reads: “1608.2: Ground Snow Loads. Delete entire section and replace with the following: The ground snow loads shall be determined using factors and methodology contained in the publication entitled Ground and Roof Snow Loads for Idaho and the accompanying map entitled Normalized Ground Snow Loads For Idaho by the University of Idaho, Moscow, Idaho, 1986.”

The figure moves with elevation in Idaho, which is the hardest case for a reader: two houses a mile apart and a thousand feet apart take different numbers, and 13 states are keyed this way. The published Idaho figures run from 15 psf to 70 lbs per sq ft.

Idaho Building Code Board, Division of Occupational and Professional Licenses adopts International Residential Code, 2018 Edition (2018 Edition). Idaho adopted it as written. The adopting rule reads: “International Residential Code, 2018 Edition. Parts I, II, III, and IX of the 2018 Edition for one (1)- and two (2)- family dwellings, with the following amendments:”

A ground snow load is a weight per unit area and not a depth, and the two are joined only by the density of the snow on the day, which is why the published documents give the load and leave the depth out. Wet spring snow and dry January snow of the same depth are different weights on the same roof. The city or county building department works in loads for that reason, and so does every figure set out below.

A Idaho figure for an address the documents below do not cover comes from the city or county building department. The document behind it is Rules of Building Safety (Building Code Rules), published by Idaho Building Code Board, read on September 23, 2026. It establishes the point this way: “The rule adopts the specific editions of the building codes prescribed by Idaho Code, and adopted by the Idaho Building Code Board, along with amendments to such building codes as determined by the Board.”

14 of 50: Connecticut, Indiana, Maryland, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New Jersey, North Carolina, Rhode Island, Utah, Vermont, Wisconsin. The other 36 split into 17 that adopt the national code without a snow amendment and 19 that leave every figure to a county or city building department. That is the single most useful fact about this subject and no one state's own website carries it.