Mobile does not allow ADUs by right on most residential lots. The Unified Development Code adopted July 12, 2022 (Ord. 64-017-2022) defines an ADU in Article 8 and lists it in the parking table (1 space), but the adopted Use Table (Sec. 64-2-24.1) has no ADU row and the R-A and R-1 districts are capped at one dwelling per lot; the draft ADU section (old Sec. 64-4-2, 1,000 sq ft cap) was dropped before adoption. Two real paths exist: an R-2 lot can add a second unit by right as a two-family dwelling within R-2 density (20 units/acre Urban, 10 Suburban), and inside the Downtown Development District ADUs are permitted by right in the T-3, T-4, T-5.1 and SD-WH transects. Anywhere else, ask Planning & Zoning (251-208-5895) for a similar-use determination before you design; the 2023 fair-housing plan recommends legalising ADUs by right within 2-3 years, but no ordinance had been filed as of September 2026.
Zoning & Size Requirements [1][2][3][4][5][6][7][8]
Sometimes — Mobile allows ADUs, but not by right on a typical lot. The adopted UDC (Ord. 64-017-2022) lists no Accessory Dwelling Unit in its Use Table and caps R-A and R-1 lots at one dwelling, so outside downtown an ADU needs a Planning Director similar-use determination or a Board of Zoning Adjustment variance. R-2 lots can add a second unit by right as a two-family dwelling, and the Downtown Development District allows ADUs by right in T-3, T-4, T-5.1 and SD-WH.
| Allowed Zones | Not listed in the UDC Use Table (Sec. 64-2-24.1); R-A and R-1 permit 1 dwelling per lot. By right only inside the Downtown Development District in T-3, T-4, T-5.1 and SD-WH (Appendix A use table). In R-2 a second unit is allowed as a Two-Family dwelling. Elsewhere an unlisted use needs a Planning Director determination (Sec. 64-2-24) or a BZA variance |
| Max Size (Detached) | No ADU size cap is codified (the 1,000 sq ft / 50% draft rule was not adopted). A second unit must fit the district lot coverage: R-1 Urban 50%, R-1 Suburban 35%, R-2 Urban 50%, R-2 Suburban 40%, R-A 35% (Secs. 64-2-4 to 64-2-6) |
| Max Size (Attached) | No ADU-specific cap; an attached second unit in R-2 counts as a Two-Family dwelling and must meet R-2 lot area (4,000 sq ft per unit Urban, 8,000 sq ft Suburban) and coverage limits (Sec. 64-2-6) |
| Max Size (JADU) | No JADU category in Mobile's UDC |
| Max Height | District height limit: 35 ft in R-A, R-1 and R-2 (Secs. 64-2-4 to 64-2-6). Downtown, outbuildings are limited to 2 stories in T-3 and T-4 and to the principal building's height elsewhere (Appendix A) |
| Max Units | R-A and R-1: 1 dwelling per lot (density row, Secs. 64-2-4 and 64-2-5). R-2: 20 units/acre Urban or 10 units/acre Suburban (Sec. 64-2-6), so a second unit fits on most R-2 lots |
Setback Requirements [1][2][3][4][5][6][7][8]
Mobile requires a rear setback of about 5 ft for a detached ADU, and parking requirements vary by unit size or location. Owner-occupancy is not required — you can rent it out without living on the property.
| Rear Setback | District rear yard applies to any dwelling: R-1 Urban 5 ft, R-1 Suburban 8 ft, R-2 Urban 5 ft, R-2 Suburban 8 ft, R-A 10 ft (Secs. 64-2-4 to 64-2-6); Historic District Overlay (Art. 14) can override. No accessory-dwelling setback reduction is codified |
| Side Setback | District side yard: 5 ft in R-1 and R-2 (Urban and Suburban), 10 ft in R-A (Secs. 64-2-4 to 64-2-6) |
| Front Setback | District front yard: 5 ft in R-1 Urban and R-2 Urban, 25 ft in R-1 Suburban, R-2 Suburban and R-A (Secs. 64-2-4 to 64-2-6) |
| Parking Required | 1 space per Accessory Dwelling Unit (Table 64-3-12.1), on top of 2 per single-family dwelling; no minimum parking inside the Downtown Development District or Spring Hill Overlay (Sec. 64-3-12) |
| Owner Occupancy | No owner-occupancy rule exists in the UDC for ADUs or two-family dwellings; any condition would come from a BZA variance or Director determination |
| Min Lot Size | District minimums: R-1 Urban 6,000 sq ft, R-1 Suburban 7,200 sq ft, R-2 Urban 4,000 sq ft per dwelling unit, R-2 Suburban 8,000 sq ft, R-A 1 acre (Secs. 64-2-4 to 64-2-6) |
Permit Process & Fees [9][10][11]
An ADU permit in Mobile goes through a standard permit review. Review time: not published. Build Mobile posts no target review time for residential plans; the residential checklist says to contact Permitting (251-208-7198) once all reviews are complete to schedule permit issuance. Permit fees: Ordinance 28-052 (eff. Jan. 2023): new construction pays $5.50 per $1,000 of valuation to $50,000, then $4.50 per $1,000, with valuation set at $86/sq ft for 1-2 family work; an 800 sq ft unit values at $68,800 for a permit fee of about $360. First residential plan review is free.
| Approval Process | Zoning first: ask Planning & Zoning (251-208-5895) whether your lot is R-2 or in the DDD, or request a similar-use determination / BZA variance for R-1. Then a residential building permit through Build Mobile's online CSS portal (2021 IRC, 2020 NEC, 2015 IECC); Historic District lots need an Architectural Review Board Certificate of Appropriateness and DDD lots a Consolidated Review Committee letter before permit |
| Review Timeline | Not published. Build Mobile posts no target review time for residential plans; the residential checklist says to contact Permitting (251-208-7198) once all reviews are complete to schedule permit issuance. |
| Permit Fees | Ordinance 28-052 (eff. Jan. 2023): new construction pays $5.50 per $1,000 of valuation to $50,000, then $4.50 per $1,000, with valuation set at $86/sq ft for 1-2 family work; an 800 sq ft unit values at $68,800 for a permit fee of about $360. First residential plan review is free. |
| Impact Fees | None. Ordinance 28-052 and the UDC contain no impact or capacity fee; water and sewer connection charges are billed separately by MAWSS |
| Plan Check | Residential plan review through the CSS portal: no fee on first submittal, then $51, $101, $201 and $501 for the 1st-4th resubmittals; a $51 plan review fee applies in flood zones or for plans over 4,000 sq ft (Residential Plan Review Checklist, Jan. 2023) |
| Pre-Approved Plans | None |
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Construction Costs [12]
Building an ADU in Mobile typically costs $90,000-$175,000 ($120-$195 per sq ft); a garage conversion runs $40,000-$90,000.
See what this means for your lot — ask Mobile ADU builders for a quote →
| 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 |
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Rental Income Potential [13]
A 2-bedroom ADU in Mobile rents for around $900-$1,300/mo, an estimated 5-8% annual return.
| Avg Rent (1 Bedroom) | $750-$1,100/mo |
| Avg Rent (2 Bedroom) | $900-$1,300/mo |
| Short-Term Rental | Short-Term Rentals (stays under 180 consecutive days) are a Conditional Use in R-A, R-1, R-2, R-3 and R-B, so a City Council Conditional Use Permit is required before listing any unit (Use Table Sec. 64-2-24.1; Art. |
| Est. Annual ROI | 5-8% annual return |
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Recent Law Changes
What's Changed Recently
- September 20, 2026: entry re-verified against the adopted UDC articles on cityofmobile.gov/udc — the ADU section (draft Sec. 64-4-2) never made it into the adopted code; status changed from by-right to discretionary
- June 3, 2025: City Council amended UDC Articles 3, 5 and 8 and adopted the Historic Avenue Overlay (Art. 15); no ADU change
- March 2025-April 2026: amendments to downtown parking exemptions, neighborhood meetings (64-5-4), PUDs (64-5-8, 64-5-8.1) and Lot of Record (64-8-2); DDD reformatting adopted early 2026 and further DDD amendments heard June 2, 2026 — none touch ADUs
- November 8, 2022: Ordinance 28-052 set the current building permit fee schedule (effective January 2023)
- July 12, 2022: Ordinance 64-017-2022 adopted the Unified Development Code, effective 2023
Tips for Building an ADU in Mobile
- Check your zoning district before anything else: an R-2 lot can take a second unit by right as a two-family dwelling, an R-1 lot cannot without a Director determination or BZA variance
- Inside the Downtown Development District (T-3, T-4, T-5.1, SD-WH) an ADU is a by-right use with no parking minimum, but your plans go through the Consolidated Review Committee first
- Historic districts such as Oakleigh and Old Dauphin Way add an Architectural Review Board Certificate of Appropriateness before the building permit; Article 14 dimensional rules can override the district setbacks
- Budget the permit from the valuation table: a 1,000 sq ft unit values at $86,000 under Ordinance 28-052, so expect roughly $440 in combined building-trade permit fees plus MAWSS connection charges
- Cost basis: the cost ranges are national industry guide figures adjusted for Alabama's lower labor and material costs; no Mobile-specific 2026 builder survey was available, so get three local bids before committing
- Cost basis (2026-09-20 re-verification): short term allowed: Short-Term Rentals (stays under 180 consecutive days) are a Conditional Use in R-A, R-1, R-2, R-3 and R-B, so a City Council Conditional Use Permit is required before listing any unit (Use Table Sec. 64-2-24.1; Art. 8 definition)
ADU Builders in Mobile
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Sources & References
All data on this page is sourced from official government records and verified market data. View our full methodology.
- City of Mobile — Unified Development Code (Ordinance 64-017-2022) article index, current versions city_website — Accessed 2026-09-20
- Mobile UDC Article 2 Zoning Districts (as amended May 17, 2022) — Secs. 64-2-4 to 64-2-6 R-A/R-1/R-2 tables; Sec. 64-2-24.1 Use Table Municipal Code — Accessed 2026-09-20
- Mobile UDC Article 4 Use Regulations as adopted July 12, 2022 (no ADU section; Sec. 64-4-2 is Home Occupations) Municipal Code — Accessed 2026-09-20
- Mobile UDC Article 8 Definitions (amended June 3, 2025) — Accessory Dwelling Unit and Short-Term Rental definitions Municipal Code — Accessed 2026-09-20
- Mobile UDC Article 3 Development Standards (adopted June 3, 2025) — Table 64-3-12.1 Minimum Parking Spaces Municipal Code — Accessed 2026-09-20
- Mobile UDC Appendix A Downtown Development District (amended May 17, 2022) — use table and outbuilding standards Municipal Code — Accessed 2026-09-20
- Map for Mobile — UDC adoption timeline and approved amendments March 2025-April 2026 city_website — Accessed 2026-09-20
- City of Mobile Analysis of Impediments to Fair Housing Choice (May 2023) — Impediment 6.1, allow ADUs by right city_website — Accessed 2026-09-20
- Ordinance 28-052 Building Codes Permit Fee Schedule (adopted November 8, 2022) — Article Seven B and Table 1 Municipal Code — Accessed 2026-09-20
- Build Mobile Residential Plan Review Checklist (revised January 2023) city_website — Accessed 2026-09-20
- Build Mobile — Forms, Applications and Codes city_website — Accessed 2026-09-20
- Calculating the Costs of Accessory Dwelling Units — BuildingAnADU (national baseline; Alabama runs 20-30% below) industry — Accessed 2026-09-20
- HUD FY2026 Small Area Fair Market Rents — Mobile, AL MSA (City of Mobile ZIP codes 36602-36695) government — Accessed 2026-09-20
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