Anchorage, AK Accessory Structures: ADU Permits (2026)

Anchorage's 2023 ADU reform (AO 2022-107) replaced the previous Title 21.05 framework with one of Alaska's most permissive ADU regimes. Under the updated standards: (1) ADUs are now permitted in all residential and commercial zones that allow a dwelling unit, including R-1, R-2, R-3, R-4, R-4A, B-1A, B-3 and others — substantially broader than the pre-2023 R-2 through R-4 limitation; (2) maximum gross floor area is 900 sq ft or 40 percent of the principal dwelling, whichever is larger, with an absolute cap of 1,200 sq ft; (3) detached, attached, and internal (basement/attic/garage-conversion) configurations are all permitted; (4) the unit must contain independent cooking, sleeping, and sanitation facilities. Building permits flow through the Development Services Department under Title 23 (Anchorage Building Code), which adopts the 2018 IBC/IRC with Alaska amendments addressing snow load (typically 50 psf ground snow in Anchorage Bowl, higher at elevation), frost depth (foundations must extend ~10 ft below grade or use approved frost-protected shallow foundation per IRC R403.3), and ice damming. The Anchorage Fire Code (Title 15, adopting the 2018 IFC) governs egress, smoke/CO alarms, and separation. ADUs must be built to two-family dwelling construction standards per the historical Title 21.05.070 framework. Anchorage launched a Pre-Approved ADU Plans program in March 2026 offering free architectural plan sets to streamline permitting. Hillside Overlay properties face additional review for wildland-urban interface fire risk, slope stability, and viewshed.