Accessory Structures in Mobile, AL

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 3 specific rules on the books covering different aspects of accessory structures, and some of them might surprise you.

Tiny Homes

Mobile's residential building code amendments formally adopt IRC Appendix AQ, the tiny house standards, giving tiny homes a recognized construction path under the city's code.

Key details: Appendix adopted: AQ - Tiny Houses. Part of: 2021 IRC amendments. Ordinance adopted: November 8, 2022. Default IRC violation fine: $250.

Building a tiny house without a permit or outside Appendix AQ's adopted standards is a Residential Code violation; Sec. 28-52 sets a default fine of $250.00 for IRC violations, rising to $300.00 for occupying without a certificate of occupancy.

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

Shed & Carport Rules

Mobile's UDC sets no separate size or height limit for sheds; accessory structures must stay out of required yards like any building, except for narrow encroachments listed in Table 64-3-5.1, such as an alley-loaded detached garage.

Key details: Shed-specific size cap: None found in UDC. Default rule: Must clear required yard setbacks. Garage exception: Alley-loaded garage: no rear-yard limit. Governing table: Table 64-3-5.1 Encroachments.

Placing a shed or storage building inside a required yard without qualifying for a listed exception under Table 64-3-5.1 is a zoning violation and can draw a stop-work order or removal notice from code enforcement.

ADU Rules

In Mobile's Historic Avenue Overlay, one accessory dwelling unit is allowed by right per single-family lot, capped at 50 percent of the main house's floor area and no taller than the principal dwelling.

Key details: Size cap: 50% of main house's floor area. Height cap: no taller than principal home. Location: behind the principal dwelling. Where it applies: Historic Avenue Overlay lots only.

Building an ADU that's oversized, taller than the main house, sited in front of it, or placed on an ineligible lot is a UDC violation subject to stop-work orders and withheld permits.

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.