Complete 2026 cost breakdown: construction, permits, financing, and expected rental ROI.
Calculate your Mobile ADU cost →Building an ADU in Mobile costs between $90,000-$175,000 for new construction, with per-square-foot costs averaging $120-$195. These figures include design, permitting, site preparation, and construction. The most affordable option is a garage conversion at $40,000-$90,000, while prefab/modular ADUs fall in between at $70,000-$150,000.
| Cost Category | Estimated Range |
|---|---|
| Architectural Plans | $3,000 – $15,000 |
| Permits & 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 |
| Site Prep & Foundation | $10,000 – $35,000 |
| Framing & Structure | $15,000 – $45,000 |
| Plumbing | $8,000 – $20,000 |
| Electrical | $5,000 – $15,000 |
| HVAC | $3,000 – $8,000 |
| Interior Finishes | $15,000 – $40,000 |
Quotes for the same ADU commonly vary 20–40% between builders. We pass your request to up to 5 local builders serving Mobile, where we have them — free, no obligation.
Get Mobile builder quotes →Permit fees in Mobile are 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.. The review timeline is 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., with 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). Impact fees are None. Ordinance 28-052 and the UDC contain no impact or capacity fee; water and sewer connection charges are billed separately by MAWSS. Pre-approved plans: None.
| 1-Bedroom Rent | $750-$1,100/month |
| 2-Bedroom Rent | $900-$1,300/month |
| Annual Rental Income (est.) | $11,100/year |
| Payback Period (est.) | 11.9 years |
| 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. |
| Overall ROI Estimate | 5-8% annual return |
A typical ADU in Mobile generates approximately $11,100 per year in rental income based on average 1-bedroom rents. At an average construction cost of $132,500, the estimated payback period is 11.9 years — before accounting for the resale value the ADU adds, which an appraiser determines from comparable sales in Mobile and varies by market (often less than build cost).
1. Garage conversions save 40-60% vs new construction since the shell already exists. Average cost in Mobile: $40,000-$90,000.
2. Prefab/modular ADUs offer predictable pricing and faster timelines. Average: $70,000-$150,000.
3. Pre-approved plans — Mobile does not offer a pre-approved/standard ADU plan program yet, so budget for custom architectural plans (typically $3,000-$15,000). See which cities offer pre-approved ADU plans.
4. State grants — California's CalHFA ADU grant (up to $40K) is currently paused; check calhfa.ca.gov/adu for status and your state for active programs.
5. Get multiple bids — ADU contractor pricing varies 20-40% for the same project. We recommend getting at least 3 quotes.
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