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Matanuska-Susitna Borough, AK Accessory Structures: ADU Rules (2026)

Some Restrictions

Compiled from the official code textEditor Martyn O'NeillLast verified September 2026

ADU rules in Matanuska-Susitna Borough, AK, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.

Key Facts

Max ADUs: Two per lot
Floor area cap: 50% of principal dwelling floor area
Permitted users: Guests, family, or domestic/health care providers
Location options: Inside home, garage apartment, or standalone
Applies to: 3 designated SFR Land Use Districts only

ADU Eligibility Quick-Check

An Accessory Dwelling Unit (ADU) is a smaller, independent living unit on the same lot as a single-family home: converted garages, detached cottages, basement or attic conversions, and attached additions all qualify. Most states have streamlined ADU permitting since 2020, but local rules still control size, height, and setback.

Is your lot zoned single-family or multi-family residential?
Does your lot have at least 1,200 sq ft of buildable space?
Is your existing home owner-occupied (in most states this is not required, but some require it for ADU permits)?
Will the ADU stay under your state's size cap (commonly 850-1,200 sq ft for detached)?
Can you provide one off-street parking space (waived in many states within 0.5 mi of transit)?

If you answered 'yes' to most of these, you likely qualify in Alaska under recent ADU streamlining laws. The Matanuska-Susitna Borough, AK rules below cover local size, height, and setback requirements.

Summary

Homeowners in the borough's Single-Family Residential Land Use Districts, Canoe Lake Subdivision, Chugach View Estates and Wilderness East Subdivision, may add up to two accessory dwelling units for guests, family or care providers, capped at a combined 50 percent of the principal dwelling's floor area, under § 17.75.060(B)(5). An ADU can sit inside the house, in a garage apartment, or as its own structure.

These county ordinances apply to unincorporated areas of Matanuska-Susitna Borough. Incorporated cities within the county may have their own rules that take precedence over county-level regulations.

Two accessory dwelling units designed and used for guests, family members, or persons providing domestic or health services to the residents of the principal structure on the same lot. The total combined floor area of the accessory dwelling units may not exceed 50 percent of the principal dwelling unit floor area. The accessory dwelling unit may be located within the principal dwelling structure, within an accessory structure such as a garage with an apartment, or be a separate accessory structure; and

View official code

Full Breakdown

035, Canoe Lake Subdivision, Chugach View Estates and Wilderness East Subdivision, and not to the borough generally. The ADUs must be designed and used for guests, family members, or persons providing domestic or health services to the residents of the principal structure on the same lot; the code does not list them as independent rental units for the general public under this accessory-use provision. Their combined floor area cannot exceed 50 percent of the principal dwelling unit's floor area. 160.

Violations & Fines

An accessory dwelling unit that exceeds the 50 percent floor-area cap, or that is used by anyone other than guests, family or care providers as § 17.75.060(B)(5) specifies, is a violation of Chapter 17.75. Under § 17.75.190, this is a borough infraction, with penalties running through MSB Chapter 1.45 and a fine capped at $1,000 under § 1.45.080(A).

Frequently Asked Questions

How many accessory dwelling units can I build in a Mat-Su SFR district?

Up to two, under § 17.75.060(B)(5), and only inside the borough's designated Single-Family Residential Land Use Districts, currently Canoe Lake Subdivision, Chugach View Estates and Wilderness East Subdivision. Their combined floor area cannot exceed 50 percent of the principal dwelling.

Can I rent an ADU to anyone in Mat-Su, or just family?

Section 17.75.060(B)(5) lists the permitted-use ADU as being for guests, family members, or persons providing domestic or health services to the principal structure's residents; it is not listed as a use for unrelated, general-public rental.

Can an ADU be a separate building from the house?

Yes. Section 17.75.060(B)(5) allows the accessory dwelling unit to be located within the principal dwelling, within an accessory structure such as a garage apartment, or as a separate freestanding accessory structure on the same lot.

Sources & Official References

[1]Matanuska-Susitna Borough Code (eCode360)

Other rules in Matanuska-Susitna Borough

Noise Ordinances: Quiet HoursSome Restrictions Shed & Carport RulesSome Restrictions Parking Rules: RV & Boat ParkingFew Restrictions Noise Ordinances: Barking DogsSome Restrictions Noise Ordinances: Decibel LimitsSome Restrictions Fence Regulations: Material RestrictionsLight Restrictions Fence Regulations: Fence Permit RequirementsFew Restrictions

All Matanuska-Susitna Borough rules

How Matanuska-Susitna Borough compares: Easiest Cities to Build an ADU·Compare Matanuska-Susitna Borough to another location·View the Alaska accessory structures overview

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