Accessory Structures in Mobile, AL: What Residents Actually Need to Know

If you live in Mobile or are thinking about moving there, accessory structures are one of those things you probably won't think about until they affect you directly. Mobile has 9 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Carport Rules

Carports in Mobile are accessory structures regulated by the Mobile Unified Development Code (Chapter 64, Zoning) and require a building permit from Build Mobile. Construction must meet Alabama-adopted IRC wind-load requirements for the Gulf Coast hurricane zone, plus the underlying district setbacks, height, and lot-coverage limits.

Key details: Authority: Mobile Unified Development Code, Ch. 64. Setbacks/Height: Per zoning district (Article 2). Building Code: AL-adopted IRC, high-wind coastal design. Permit: Required from Build Mobile. Front Yard: Generally not permitted.

Building a carport without a permit, exceeding district height or lot coverage, encroaching into a required setback, or failing to meet wind-load and floodplain construction standards is a zoning and building violation. Remedies under Chapter 64 and Chapter 11 include stop-work orders, retroactive permitting, removal of non-conforming structures, and fines.

Tiny Homes

Mobile's Unified Development Code (Chapter 64, June 2022) authorizes Accessory Dwelling Units in residential districts on lots permitting a single dwelling. ADUs must be smaller than the primary residence, sit on a permanent foundation, and obtain a building permit. Alabama has no statewide tiny-home preemption; the state-adopted IRC governs minimum dwelling standards.

Key details: Authority: Mobile UDC, Ch. 64 (ADU provisions). ADU Size: ~800-1,000 sq ft or 40% of primary (verify). Foundation: Permanent required. Per Lot: One ADU per residential lot. Parking: 1 off-street space.

Constructing or occupying an unpermitted ADU or tiny home, exceeding the ADU size cap, separating ownership from the principal dwelling, or operating an ADU as a short-term rental in violation of Chapter 64 is a zoning violation. Build Mobile may issue stop-work orders, require retroactive permitting or removal, and assess fines under Chapter 11 and Chapter 64.

ADU Owner Occupancy

The Mobile Unified Development Code (Chapter 64) treats ADUs as accessory uses subordinate to the principal single-family dwelling and prohibits separate sale of the ADU from the main dwelling. The practical effect is an owner-presence expectation: the principal dwelling must remain occupied as a single-family residence, with the ADU used as accessory space. Alabama has not preempted local ADU rules. Variances or zoning changes are pursued through the Mobile Board of Zoning Adjustment or Planning Commission.

Key details: Citywide Mandate: Subordinate-use rule (UDC). Separate Sale: Prohibited. STR Use: Historically prohibited. State Preemption: None (Dillon Rule). Variance Path: Board of Zoning Adjustment.

Operating an accessory dwelling as a fully independent rental in a single-family residential district can be cited as a zoning violation under Chapter 64, with code-enforcement orders requiring cessation of the rental use. Continued violation accrues daily fines under the city's general penalty provisions. Selling the ADU as a separate parcel violates UDC accessory-use provisions and can void title transfers.

ADU Permits

Mobile authorizes accessory dwelling units (ADUs) under the Mobile Unified Development Code (Code of Ordinances Chapter 64), adopted June 7, 2022. ADUs are allowed in residential districts on lots permitting a single dwelling, must sit on a permanent foundation, and require a building permit through Build Mobile (Permitting & Inspections Division). Alabama is a Dillon Rule state with no statewide ADU preemption. Construction follows the Alabama-adopted International Residential Code with Gulf Coast hurricane wind-load amendments.

Key details: Authority: Mobile UDC, Ch. 64 (June 2022). State Preemption: None (Dillon Rule). Permit Office: Build Mobile (251-208-5895). Building Code: AL-adopted IRC (high-wind). Historic Districts: Architectural Review Board COA.

Constructing an ADU without a permit violates Code Chapters 11 and 64, triggering stop-work orders from Build Mobile, after-the-fact permit fees, and zoning enforcement under the UDC. Unpermitted electrical, plumbing, or gas work voids homeowner insurance. Historic district violations carry separate Architectural Review Board enforcement. Daily fines accrue under the city's general penalty provisions.

ADU Impact Fees

Mobile does not impose a general residential impact fee on accessory dwelling units. Alabama law does not broadly authorize municipal residential impact fees outside specific statutory grants. ADU costs include standard building, electrical, plumbing, and mechanical permit fees through Build Mobile plus tap/connection fees from the Mobile Area Water and Sewer System (MAWSS) and Alabama Power if a new utility service is required.

Key details: General Impact Fee: None. School Impact Fee: None (Mobile County). Permit Fees: Construction-valuation basis. Water/Sewer: MAWSS tap fees if new service. Electric: Alabama Power service charges.

Failure to pay required permit fees prevents permit issuance. Unpaid MAWSS or Alabama Power connection fees prevent service activation. Building without permits triggers after-the-fact fees and stop-work orders under Code Chapters 11 and 64, plus accruing daily fines under the city's general penalty provisions.

If you are coming from a city with tighter rules, you will find Mobile gives residents more flexibility on adu impact fees.

ADU Rental Restrictions

The Mobile Unified Development Code (Chapter 64) historically prohibits use of an accessory dwelling unit as a short-term rental, and ADUs cannot be sold separately from the principal dwelling. Long-term rental of an ADU as a fully separate tenancy generally requires zoning that permits a two-family dwelling. Short-term rental operations citywide require a city business license under Code Chapter 34 and collection of city, county, and state lodgings taxes. Alabama has not preempted local STR rules.

Key details: ADU STR Use: Historically prohibited (UDC). ADU Long-Term Rental: Subject to subordinate-use rule. STR Business License: Code Ch. 34. State Lodgings Tax: 5% (AL Dept. of Revenue). City/County Lodgings Tax: Mobile + Mobile County add.

Operating an unlicensed STR in Mobile violates Code Chapter 34 (Business Licenses) and the lodgings-tax provisions, with administrative penalties and back-tax liability. Operating an ADU as a short-term rental violates Chapter 64 (UDC), with code-enforcement orders and daily fines under the city's general penalty provisions. The Alabama Department of Revenue pursues separate state lodgings-tax enforcement.

Compared to other cities, Mobile takes a harder line on adu rental restrictions. The enforcement and penalty structure reflects that.

ADU Rules

Mobile allows one ADU per single-family lot under the unified development code. Size is generally limited to 1,000–1,200 square feet or a percentage of the primary dwelling. ADUs must meet building code standards.

Key details: Limit: One ADU per single-family lot. Size: 1,000–1,200 sq ft max. Building Code: Residential standards apply. Permit: Building permit required.

ADUs built without permits or exceeding size limits face code enforcement action.

Shed Rules

Mobile regulates sheds through zoning setbacks and size limits. Small sheds under 120 square feet typically do not require a building permit but must meet setback requirements.

Key details: No Permit: Under 120 sq ft. Setbacks: 3–5 feet from property lines. Location: Rear or side yard. Living Quarters: Not permitted without ADU approval.

Sheds violating setbacks or without required permits may need to be relocated or removed.

Garage Conversions

Mobile allows garage conversions to living space with a building permit. The converted space must meet residential building code and parking requirements must still be met.

Key details: Permit: Building permit required. Code: Residential building code applies. Parking: Must maintain minimum parking. ADU Option: May qualify under UDC.

Unpermitted conversions result in code enforcement action.

The Bottom Line

Mobile's accessory structures rules are a mixed bag. Some areas are strict, others are relaxed, and the details matter. The best approach is to check the specific rule that applies to your situation rather than assuming Mobile is broadly strict or permissive.

All of the above reflects Mobile's municipal code as of our last review. If you need specifics on fines, exemptions, or filing requirements, the detailed ordinance pages linked above have the full breakdown.