Everything homeowners ask about building an ADU in Mobile — answered with 2026 data.
Yes, ADUs are allowed in 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) in Mobile, AL. The maximum size for a detached ADU is 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)). Attached ADUs can be up to Same standard — 1,000 sq ft or 50% of principal structure, whichever is less; may be adapted from a portion of the principal dwelling. Mobile has an ADU-friendliness score of 6/10. Check our full Mobile ADU rules page for complete zoning details.
ADU construction in Mobile typically costs $90,000-$175,000. The cost per square foot averages $120-$195. Garage conversions are more affordable at $40,000-$90,000, while prefab ADUs cost $70,000-$150,000. Permit fees add Per the City of Mobile permit fee schedule — confirm current amounts with Build Mobile Permitting & Inspections Division to your budget. See our detailed Mobile ADU cost guide.
Detached ADUs in Mobile can be up to 1,000 sq ft gross floor area or 50% of the principal structure's floor area, whichever is less. Attached ADUs are limited to Same standard — 1,000 sq ft or 50% of principal structure, whichever is less; may be adapted from a portion of the principal dwelling. Junior ADUs (JADUs) have a cap of No JADU category in Mobile's UDC. Maximum height is 2 stories or the height of the principal dwelling, whichever is less (Sec. 64-4-2.B.3(b)). You are allowed up to 1 ADU per property on a qualifying lot.
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. Note that garage conversions may be exempt from setback requirements if the existing structure is already within the setback area.
At least 1 off-street parking space for the ADU (Sec. 64-4-2.B.6). Many cities and states have been relaxing ADU parking requirements in recent years. In California, no additional parking is required for ADUs near transit.
Not required by Sec. 64-4-2; confirm current administrative practice with Mobile Planning & Zoning. Note that owner-occupancy rules vary by state law — California and several other states have eliminated this requirement for standard ADUs.
The ADU permit review timeline in Mobile is typically Confirm with Build Mobile Permitting & Inspections Division; pre-development meetings available. Plan check: Plan review submitted through the Build Mobile CSS online portal; confirm review times with Build Mobile. Pre-approved plans availability: None.
Average ADU rental income in Mobile: 1-bedroom units rent for $1,000-$1,200/month, 2-bedroom units for $1,150-$1,450/month. Short-term rentals: Not addressed in the ADU section (Sec. 64-4-2) — confirm short-term rental rules with Mobile Planning & Zoning before listing. Expected ROI: 5-8% annual return.
The minimum lot size for an ADU in Mobile is 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)). This applies to detached ADUs — garage conversions and JADUs may have different or no lot size requirements.
Garage conversions are one of the most popular and affordable ADU options. In Mobile, a garage conversion typically costs $40,000-$90,000. The key advantages are lower cost (no foundation work), potential setback exemptions, and faster permitting. Read our complete garage conversion guide.
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