St. Louis County, MN Accessory Structures: ADU Rules (2026)
ADU rules in St. Louis County, MN, also called accessory dwelling unit regulations or granny flat ordinances, cover setbacks, owner-occupancy, parking, and permit requirements.
Key Facts
- Shoreland lot 1+ acre: max size/height
- 700 sq ft / 20 ft
- Shoreland lot under 1 acre: max size/height
- 250 sq ft / 14 ft
- Nonshoreland lot: max size
- 1,200 sq ft
- Permit required for all tiers
- Land use permit
- Over the size cap
- Treated as a principal dwelling
Summary
An accessory dwelling in unincorporated St. Louis County always needs a land use permit, and its allowed size and height depend on the lot: up to 700 square feet and 20 feet tall on a shoreland acre or larger, 250 square feet and 14 feet on smaller shoreland lots, or 1,200 square feet in nonshoreland areas.
Section 6.11 Accessory Dwelling Administrative Standards “V” A. Permit Required: General: An accessory dwelling is defined as an accessory structure used as a dwelling unit that may contain sleeping spaces, and kitchen and bathroom facilities, in addition to those provided in the principal dwelling structure and may be allowed with a land use permit. B. Accessory Dwellings in Shoreland Areas One Acre is Size or Greater: An accessory dwelling may be allowed with a land use permit if the following standards are met: 1. One accessory dwelling may be allowed per lot or parcel that is a minimum of one acre in size. 2. Maximum size allowed shall be 700 square feet in floor area. A proposed accessory dwelling that exceeds 700 square feet shall be considered a principal dwelling. 3. Maximum height allowed shall be 20 feet.
Full Breakdown
A defines an accessory dwelling as an accessory structure with sleeping, kitchen and bathroom facilities beyond the principal dwelling, allowed only with a land use permit. Three tiers of standards follow. B, a shoreland parcel of one acre or larger may have one accessory dwelling capped at 700 square feet of floor area and 20 feet in height; exceed 700 square feet and the county treats it as a principal dwelling instead, which triggers a different set of dimensional and dwelling-count rules. 7. D, nonshoreland parcels get the most room: one accessory dwelling up to 1,200 square feet, with no separate height cap stated beyond the general accessory-structure rules, and it may be combined with a garage.
Every tier requires adequate septic capacity that accounts for the principal structure's own demand, compliance with the accessory structure setback for that zone district, and compliance with the district's lot coverage limit. C must also be screened from public waters by natural means.
Violations & Fines
Building or occupying an accessory dwelling without a land use permit, or one that exceeds its tier's size or height cap, is a zoning violation under Article VIII. The Director notifies the owner and sets a correction period under Section 8.2.A; an oversized structure that is not corrected can be treated as an unpermitted principal dwelling, and continued non-compliance is a misdemeanor under Section 8.2.B.
Frequently Asked Questions
How big can an accessory dwelling be on my St. Louis County lake lot?
Can I combine an accessory dwelling with a garage?
What happens if my accessory dwelling is bigger than the code allows?
Sources & Official References
Other rules in St. Louis County
How St. Louis County compares: Easiest Cities to Build an ADU·Compare St. Louis County to another location·View the Minnesota accessory structures overview
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