Anchorage, AK Accessory Structures: ADU Rules (2026)
ADU rules in Anchorage, AK, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Max size
- 1,200 sq ft absolute cap
- Size formula
- 900 sq ft or 40% of home
- Max height
- 25 ft (30 ft over garage)
- Units per parcel
- One ADU allowed
- Permit needed
- Building or land use permit
Summary
Anchorage caps accessory dwelling units at 1,200 square feet and 25 feet in height, allowed by right in every residential zone.
Size. The gross floor area of the ADU, not including any related garage, shall be up to 900 square feet or 40 percent of the total gross floor area of the principal dwelling unit (excluding the ADU and garages), whichever is greater, and an ADU shall not exceed 1,200 square feet.
(5) Setbacks. ADUs are subject to the same setbacks of the underlying zone except that an ADU may encroach into the side or rear setback abutting an alley. Detached accessory units taller than 15 feet shall adhere to a ten-foot side setback abutting a neighboring R-1 or R-1A lot.
(6) Utilities. To the extent allowed by law and utility tariff, the ADU shall be connected to the water, sewer, gas, and electric utilities of the single-family dwelling unit. However, lots with on-site water or septic systems may have a separate water and/or septic system for the ADU.
(C) Height. ADUs shall be a maximum limit of 25 feet in height, unless located above a garage, in which case the ADU is limited to a maximum of 30 feet in height.
(D) Density. ADUs are not included in the density calculations for a site.
(E) Expiration of approval of an ADU. Approval of an ADU expires when:
(1) The ADU is altered and is no longer in conformance with this Code;
(2) The ADU is abandoned by the landowner through written notification to the municipality on a form provided by the municipality.
(F) Prior illegal use.
(1)
Official source re-checked September 7, 2026: no newer edition of the code had been published (publisher’s edition: rev 5010260; v11 updated 2026-09-01).
Full Breakdown
The Anchorage Municipal Code allows one accessory dwelling unit per parcel in all residential zoning districts under AMC 21.05.070D.1. The ADU's gross floor area is capped at 900 square feet or 40% of the principal dwelling's floor area, whichever is greater, but never more than 1,200 square feet. Height is limited to 25 feet, or 30 feet if the unit sits above a garage. ADUs must meet the underlying zone's setbacks, though they may encroach into a side or rear setback abutting an alley, and detached units taller than 15 feet need a 10-foot side setback next to an R-1 or R-1A lot. Combined lot coverage of the principal home, garage, and ADU can't exceed the district's maximum, and ADUs are built to the same adopted building code as any other structure. A landowner must get a building or land use permit from the Development Services Department before building or establishing one.
Violations & Fines
An unpermitted or oversized ADU is an illegal accessory structure; the building official can require the owner to bring it into conformance within six months of a compliance order, and failure to legalize it triggers civil penalties under AMC 14.60.030.
Frequently Asked Questions
Can I build more than one ADU on my lot?
Do Anchorage ADUs count toward lot density?
Sources & Official References
Other rules in Anchorage
How Anchorage compares: Easiest Cities to Build an ADU·Compare Anchorage to another location·View the Alaska accessory structures overview
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