Mobile is Alabama's most ADU-friendly major city: the Unified Development Code (adopted July 12, 2022, effective early 2023) contains a dedicated ADU section (Sec. 64-4-2) allowing one ADU per property in the R-A, R-1 and R-2 districts as an accessory use. ADUs may be new construction, conversions of existing accessory structures, or carved from the principal dwelling, capped at 1,000 sq ft or 50% of the main home's floor area (whichever is less) and two stories, with one off-street parking space required. Historic-district ADUs need Architectural Review Board approval; no owner-occupancy requirement appears in the code section.
Zoning & Size Requirements [1][2]
Yes — Mobile allows ADUs. A detached ADU can typically be up to 1,000 sq ft under current Alabama and Mobile zoning rules.
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| Allowed Zones | Permitted as an accessory use per the UDC Use Table; one ADU allowed on a property in R-A, R-1 or R-2 (Sec. 64-4-2.B.2) |
| Max Size (Detached) | 1,000 sq ft gross floor area or 50% of the principal structure's floor area, whichever is less (Sec. 64-4-2.B.3(a)) |
| Max Size (Attached) | Same standard — 1,000 sq ft or 50% of principal structure, whichever is less; may be adapted from a portion of the principal dwelling |
| Max Size (JADU) | No JADU category in Mobile's UDC |
| Max Height | 2 stories or the height of the principal dwelling, whichever is less (Sec. 64-4-2.B.3(b)) |
| Max Units | 1 ADU per property |
Setback Requirements [1][2]
Mobile requires a rear setback of about 64 ft for a detached ADU, and one off-street parking space is required. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | Same as underlying zoning district rear-yard setback, or Historic District Overlay if applicable (Sec. 64-4-2.B.4(a)) — confirm district value with Mobile Planning & Zoning |
| Side Setback | Same as underlying district side-yard setback (Sec. 64-4-2.B.4(a)) |
| Front Setback | Same as underlying district front-yard setback (Sec. 64-4-2.B.4(a)); ADU may not sit in any recorded easement |
| Parking Required | At least 1 off-street parking space for the ADU (Sec. 64-4-2.B.6) |
| Owner Occupancy | Not required by Sec. 64-4-2; confirm current administrative practice with Mobile Planning & Zoning |
| Min Lot Size | No ADU-specific minimum; underlying district lot standards apply and the ADU may not push lot coverage over the district maximum (Sec. 64-4-2.B.3(c)) |
Permit Process & Fees [3][4]
An ADU permit in Mobile typically costs Per the City of Mobile permit fee schedule — confirm current amounts with Build Mobile Permitting & Inspections Division and takes Confirm with Build Mobile Permitting & Inspections Division; pre-development meetings available, through a standard permit review.
| Approval Process | Building permit through Build Mobile's Permitting & Inspections Division (online CSS portal for plans, permits and inspections); ADUs in designated Historic Districts also need Architectural Review Board approval (Sec. 64-4-2.B.5(a)); all ADU structures must meet or be brought up to current Building Code (Sec. 64-4-2.B.5(b)). Contact: 251-208-5895 |
| Review Timeline | Confirm with Build Mobile Permitting & Inspections Division; pre-development meetings available |
| Permit Fees | Per the City of Mobile permit fee schedule — confirm current amounts with Build Mobile Permitting & Inspections Division |
| Impact Fees | None identified; confirm with Build Mobile Permitting & Inspections Division |
| Plan Check | Plan review submitted through the Build Mobile CSS online portal; confirm review times with Build Mobile |
| Pre-Approved Plans | None |
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Construction Costs [5]
Building an ADU in Mobile typically costs $90,000-$175,000 ($120-$195 per sq ft); a garage conversion runs $40,000-$90,000.
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| Average Build Cost | $90,000-$175,000 |
| Cost per Sq Ft | $120-$195 |
| Garage Conversion | $40,000-$90,000 |
| Prefab ADU (Installed) | $70,000-$150,000 |
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
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Rental Income Potential [6]
A 2-bedroom ADU in Mobile rents for around $1,150-$1,450/mo, an estimated 5-8% annual return.
| Avg Rent (1 Bedroom) | $1,000-$1,200/mo |
| Avg Rent (2 Bedroom) | $1,150-$1,450/mo |
| Short-Term Rental | Not addressed in the ADU section (Sec. 64-4-2) — confirm short-term rental rules with Mobile Planning & Zoning before listing |
| Est. Annual ROI | 5-8% annual return |
Explore Prefab ADU Options
Prefab ADUs can save 20-40% vs. traditional construction and cut build time in half.
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Recent Law Changes
What's Changed Recently
- July 12, 2022: City Council unanimously adopted the new Unified Development Code, creating Mobile's first explicit by-right ADU framework (effective early 2023)
- 2025-January 2026: UDC amendments covered parking exemptions, neighborhood meetings, lot definitions and the Historic Avenue Overlay — none altered the ADU section
- April-June 2026: Planning Commission recommended Downtown Development District (Appendix A) amendments; City Council public hearing held June 2, 2026 — technical corrections, not ADU-specific
Tips for Building an ADU in Mobile
- Size your ADU against both caps: on a smaller home, 50% of the principal structure's floor area — not 1,000 sq ft — will be your binding limit
- Check your lot for recorded easements first; ADUs cannot be located in any easement (Sec. 64-4-2.B.4(b))
- In Mobile's historic districts (e.g., Oakleigh, Old Dauphin Way), budget time for Architectural Review Board approval before permitting
- Converting an existing backyard structure is allowed but it must be brought fully up to current Building Code — get a contractor assessment before assuming a cheap conversion
- Book a pre-development meeting with Build Mobile (251-208-5895) to confirm your district's setbacks and coverage math before paying for plans
ADU Builders in Mobile
Looking for an ADU builder in Mobile? ADU projects need a contractor experienced with local zoning, the permit process, and utility connections — not every general contractor has built one. We match Mobile homeowners with experienced local ADU contractors who provide free, no-obligation quotes. Getting at least three bids typically saves 20-40% on the same scope.
Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- Mobile Unified Development Code, Ch. 64 Art. 4 Use Regulations, Sec. 64-4-2 Accessory Dwelling Units Municipal Code — Accessed 2026-07-10
- Mobile's UDC — Map for Mobile (adoption timeline and amendments) city_website — Accessed 2026-07-10
- Permitting & Inspections Division — Build Mobile, City of Mobile city_website — Accessed 2026-07-10
- Mobile UDC Sec. 64-4-2.B.5 Building Standards Municipal Code — Accessed 2026-07-10
- Calculating the Costs of Accessory Dwelling Units — BuildingAnADU (national baseline; AL runs 20-30% below) news_media — Accessed 2026-07-10
- Average Rent in Mobile, AL — RentCafe (July 2, 2026) news_media — Accessed 2026-07-10
Frequently Asked Questions
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