Garage conversion rules in Benton County, WA — sometimes called garage-to-ADU or accessory living unit conversions — govern permits, ceiling height, egress, and parking replacement.
Converting a garage into living space in unincorporated Benton County is a change of occupancy needing a building permit, and if it gains a kitchen and separate entrance it becomes an ADU under HB 1337.
A garage-to-living-space conversion changes the occupancy from IRC Group U to Group R-3, so Benton County's building official requires a building permit and plan review under RCW 19.27 and WAC 51-50/51-51. The new room must meet residential minimums: adequate ceiling height, an emergency egress window in any sleeping room, smoke and carbon-monoxide alarms, insulation to the Washington State Energy Code, and structural verification of the slab and walls. Adding a bathroom or kitchen brings plumbing and electrical permits. When the conversion creates a kitchen and separate entrance on a lot inside a UGA, it becomes an accessory dwelling unit governed by HB 1337 (RCW 36.70A.681).
An unpermitted garage conversion is a code violation that can force after-the-fact permitting or restoration to a garage. Creating a second dwelling unit without ADU approval adds zoning enforcement.
Other ordinances people look up for this city. Green dot = verified primary-source excerpt.
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