Washington

Statewide summary — confirm with your building department before designing

No value on this row was changed by this audit, but the ground snow load on it is untenable as a single number. Washington is explicit that these are not state level quantities: WAC 51-51-0301 adopts IRC Section R301.2 with the direction that the additional criteria are to be established by the local jurisdiction and set out in its own Table R301.2, so there is no statewide answer by design. Ground snow load varies past the point where any scalar helps. A King County jurisdiction adopted 25 psf, matching the stored figure, while the City of Spokane adopted 39 psf and the Cascade communities carry several times that. A value that fits the Puget Sound lowlands is well below what Spokane requires, and a value that fits Spokane still misses the mountains while over building the lowlands, so no single number is defensible. Seismic design category D is confirmed and is the correct conservative envelope. The USGS ASCE 7-16 design maps service at Site Class D and Risk Category II returns 0.933 g at Seattle, 0.903 g at Tacoma, 0.939 g at Olympia, 1.011 g at Aberdeen, 0.734 g at Bellingham and 0.647 g at Vancouver, all category D, and a King County jurisdiction adopted D sub two outright. Eastern Washington is genuinely lower, at 0.318 g in Spokane, which the City of Spokane adopted as category C, and 0.446 g at Yakima, category C. Because D over covers eastern Washington rather than falling short of it, D remains the right single value even though the state is split. Wind speed of 110 mph is confirmed against two adopted tables, the City of Spokane and a King County jurisdiction, both of which adopted 110 mph. Frost depth of 24 inches matches Spokane's adopted 24 inches and over builds the King County jurisdiction's adopted 18 inches, so it errs safe. Termite risk of slight corresponds to the IRC slight to moderate band and matches Spokane's adopted value. Winter design temperature is unestablished; the adopted figures found range from 10 F at Spokane to 26 F in King County. Confirm your own lot with the local building official. Sources: https://app.leg.wa.gov/wac/default.aspx?cite=51-51-0301, https://my.spokanecity.org/smc/?Section=17F.040.105 and https://earthquake.usgs.gov/ws/building-codes/ 2026 snow-load pass. Washington publishes no statewide ground snow load and the delegation is explicit in the adopted rule, so snow_load_min_psf and snow_load_max_psf are both left null and ground snow load is corrected from 25 to null. The governing text was read from the official certified WAC PDF rather than a summary. WAC 51-51-0301, certified 3/27/2024, states that buildings shall be constructed in accordance with the provisions of this code as limited by the provisions of this section, that additional criteria shall be established by the local jurisdiction and set forth in Table R301.2, and that the local jurisdiction shall designate the salt water coastal areas within their jurisdiction. There is no statewide answer by design. The stored 25 psf came from one King County jurisdiction and is not a state figure; the City of Spokane adopted 39 psf and the Cascade communities carry several times that, so no scalar is defensible and null is the honest entry. Two further checks were run to make sure nothing statewide was being missed. First, the commercial side: chapter 51-50 WAC contains sections 1602, 1604, 1605, 1607, 1609, 1613 and 1615 but no section 1608, which is the IBC snow load section, so Washington has not amended ground snow load determination for commercial buildings either, and a full-text scan of chapter 51-50 WAC turns up a single occurrence of the word snow, in an unrelated attic ventilation provision. Second, the widely used SEAW White Paper Number 8, Guidelines for Determining Snow Loads in Washington State, is not adopted by any Washington instrument. It was proposed for adoption into IBC Section 1608.2 in SBCC proposal 24-GP1-063 filed September 12, 2024, but the December 2024 revision R2 of that same proposal drops the white paper entirely and asks only for substantiating data where the site elevation and the mapped elevation differ by more than the greater of 10 percent of site elevation and 300 feet. So even the pending proposal would not give Washington a state snow load source. That proposal belongs to the 2024 code adoption cycle, which as of this pass is still at the CR-102 proposed-rule stage with CR-103 adoption dates listed as to be determined, meaning the 2021-based codes adopted effective March 2024 remain the codes in force and the delegation in WAC 51-51-0301 stands. Because SEAW White Paper Number 8 is a professional-association document that no state instrument adopts by reference, it was not used as the source of any number here, and neither was the ASCE Hazard Tool. The four pre-existing values are unchanged by this pass: seismic design category D, wind speed 110 mph and frost depth 24 inches all remain as previously verified, and the reasoning for each is preserved above.