Ada County, ID Building Safety: Fire Sprinkler Requirements (2026)

Ada County Code 7-2-5 adopts the 2018 International Residential Code (IRC) with local amendments, and Chapter 3 "Building Planning" of that adoption rewrites the sprinkler sections that would otherwise apply countywide. Section R313.2, titled "One- and two-family dwellings automatic fire systems," is deleted in its entirety, so Ada County imposes no local requirement that a new single-family home or duplex in the unincorporated area include an automatic residential fire sprinkler system. That is a deliberate opt-out: the base 2018 IRC would have required sprinklers in nearly all new houses, and the county struck that section rather than adopting it.

Section R313.1, covering townhouse automatic fire sprinkler systems, is treated differently. The county keeps the base sprinkler requirement for townhouses but rewrites the exception: sprinklers are not required in a townhouse where either two one-hour fire-resistance-rated walls, or a single common two-hour fire-resistance-rated wall (the wall type described in IRC section R302.2.2, item 2), separates the dwelling units. The same exception carries over to additions or alterations on existing townhouses that were built without a sprinkler system, so a remodel does not trigger a retrofit requirement. In practice, a townhouse builder in unincorporated Ada County chooses between installing residential sprinklers or building the heavier fire-rated separation wall between units; there is no such choice for a standalone house or duplex, which simply falls outside R313 altogether. Permit applications go through Ada County Development Services, which reviews plans against these amended IRC chapters before issuing a building permit.