Hawaii

Statewide summary — confirm with your building department before designing

Seismic design category is corrected from B to D. The Hawaii State Residential Code assigns seismic design category by island and district for Site Class D: Kauai is B, Oahu and Molokai and Lanai are D0, Maui is D1, the North Kohala and South Kohala and Hamakua and North Hilo districts of Hawaii County are D2, and every other Hawaii County district including Kona, Kau, Puna and South Hilo is E. USGS ASCE 7-16 values agree: Honolulu and Kahului and Hilo compute to category D and Kailua-Kona computes to E, while Lihue is B. The stored B was correct only for Kauai, roughly five percent of the state population. D is the value that covers Oahu, Maui, Molokai and Lanai, about eighty five percent of residents, but it understates the Big Island, where much of Hawaii County is E and requires engineered seismic design. Termite risk is corrected from slight to very heavy. Formosan subterranean termite is established across the inhabited islands and Hawaii code requires layered protection, a soil treatment or physical barrier combined with a resistant framing material. The 130 mph wind speed is the ASCE 7 ultimate design wind speed for Risk Category II in the Hawaii State Building Code; Risk Category III is 145 mph and Risk Category IV is 153 mph, and individual counties map higher speeds in exposed terrain. Ground snow load of 0 psf, frost depth of 0 inches and a winter design temperature of 60 F describe inhabited coastal lowlands only and are wrong for upcountry Maui, Waimea, Volcano and any high elevation site. Confirm every value with your county building department before design. 2026 snow-load pass. The question of whether Hawaii code says anything at all about snow, rather than zero being assumed, was checked directly and the answer is that it does. Hawaii adopts the 2018 IBC as the Hawaii State Building Code and the 2018 IRC as the Hawaii State Residential Code under HRS chapter 107, with county adoption. Section 1608.2 of the adopted IBC ends with an explicit sentence that snow loads are zero for Hawaii, except in mountainous regions as approved by the building official. That is a real state-adopted statement and not an inference, so snow_load_min_psf is set to 0 on the strength of it, and the existing ground snow load of 0 psf is confirmed rather than merely retained. snow_load_max_psf is left null deliberately, because the same sentence declines to give a number for the mountains and hands it to the building official; this is the same pattern as a case-study zone. Mauna Kea at 13,803 feet and Mauna Loa at 13,681 feet both hold snow, and any structure there, including the Mauna Kea observatories, needs a value the state code does not supply. Two supporting checks. The Hawaii State Residential Code amendments contain zero occurrences of the word snow across the whole document; Hawaii amends R301.2 heavily for wind, adding island-by-island effective basic wind speed figures for each county, but says nothing about snow, so the unamended IRC Table R301.2 applies and the county fills the ground snow load cell in. The Hawaii State Building Code amendments mention ground snow load exactly once, in the construction-documents provision requiring pg to be shown on the drawings for conventional light-frame construction, which imposes a disclosure duty and not a value; the state does not amend IBC Section 1608. The adopted 2018 IBC text was read from a government printing of the identical model section, the City of Seattle 2018 Seattle Building Code Chapter 16, since Hawaii publishes its amendments but not its own printing of the model text. Note that these are ground snow loads, not roof snow loads. No value on this row was changed by this pass; seismic design category D, wind speed 130 mph, ground snow load 0 psf and frost depth 0 inches all stand, and the caveats recorded above, especially that much of Hawaii County computes to seismic category E and that the 0 psf and 0 inch figures describe inhabited lowlands rather than high-elevation sites, remain in force.