Zoning & Size Limits
| Requirement | Mobile, AL | Birmingham, AL |
|---|
| Allowed Zones | Permitted as an accessory use per the UDC Use Table; one ADU | ADUs are not currently permitted in most residential distric |
| 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)) | Not established — no ADU ordinance exists; confirm with Birmingham Planning Division |
| 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 | Not established — no ADU ordinance exists; confirm with Birmingham Planning Division |
| Max Height | 2 stories or the height of the principal dwelling, | Not established for ADUs; accessory structures mus |
| Parking Required | At least 1 off-street parking space for the ADU (Sec. 64-4-2 | No ADU parking standard exists; parking was a top resident c |
| Owner Occupancy | Not required by Sec. 64-4-2; confirm current administrative | Not established — absentee-landlord concerns were raised at |
Setback Requirements
| Setback | Mobile, AL | Birmingham, AL |
|---|
| 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 | Underlying district accessory-structure setbacks apply; ADU-specific standards do not exist yet — confirm with Birmingham Planning Division |
| Side Setback | Same as underlying district side-yard setback (Sec. 64-4-2.B.4(a)) | Confirm with Birmingham Planning Division |
| Front Setback | Same as underlying district front-yard setback (Se | Confirm with Birmingham Planning Division |
Permits & Timeline
| Detail | Mobile, AL | Birmingham, AL |
|---|
| Permit Timeline | Confirm with Build Mobile Permitting & Inspections Division; pre-development meetings available | N/A for ADUs; ordinance still in community-input phase (town halls June-July 2026) |
| Permit Fees | Per the City of Mobile permit fee schedule — confirm current amounts with Build Mobile Permitting & Inspections Division | Confirm with Dept. of Planning, Engineering & Permits |
| Impact Fees | None identified; confirm with Build Mobile Permitting & Insp | None identified; confirm with Dept. of Planning, Engineering |
| Pre-Approved Plans | None | None |
Construction Costs
| Cost | Mobile, AL | Birmingham, AL |
|---|
| Avg Build Cost | $90,000-$175,000 | $90,000-$180,000 |
| Cost Per Sq Ft | $120-$195 | $120-$200 |
| Garage Conversion | $40,000-$90,000 | $40,000-$95,000 |
| Prefab ADU | $70,000-$150,000 | $70,000-$150,000 |
Rental Income Potential
| Rental | Mobile, AL | Birmingham, AL |
|---|
| 1BR Avg Rent | $1,000-$1,200/mo | $1,100-$1,350/mo |
| 2BR Avg Rent | $1,150-$1,450/mo | $1,250-$1,500/mo |
| Short-Term Rentals | Not addressed in the ADU section (Sec. 64-4-2) — confirm sho | Moot for ADUs until an ordinance passes; short-term rental t |
| Est. ROI | 5-8% annual return | 5-8% annual return (hypothetical — ADUs not yet broadly permitted) |
Which City Is Better for ADUs?
Mobile scores 6/10 while Birmingham scores 3/10 on our ADU-friendliness index.
Mobile edges ahead overall. Both cities offer viable ADU development opportunities — the best choice depends on your specific property, budget, and goals.
Finance Your ADU Project
Most ADU projects are funded through HELOCs, construction loans, or cash-out refinancing. Compare rates from top lenders.
Some links on this page are affiliate links. We may earn a commission at no extra cost to you. Learn more
Get Quotes in Your City
Connect with licensed ADU contractors and get free quotes for your project.