Alabama is fully permittable for modular via the AMHC program; ADUs are city-by-city, with Huntsville and Birmingham now allowing them.
Building approval
Alabama Manufactured Housing Commission (AMHC)
Program
AMHC modular program (2021 IBC) — Third-party label, state-reviewed
ADU law
Local (Huntsville 2024, Birmingham)
ADU summary
No statewide ADU law; Huntsville (R-1) and Birmingham have opened up.
Site / structural drivers
Gulf-Coast hurricane wind + flood; inland heat/tornado
Verdict
Permittable — ADUs are local
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The Alabama Manufactured Housing Commission (AMHC) serves as the state agency enforcing the manufactured building (modular) program construction standards. Modular plan submittals must comply with the 2021 IBC (effective April 1, 2023), and modular installers must complete an AMHC course and certification. With the program's approval, your local jurisdiction permits the site work — foundation, utilities, zoning.
It depends on your city — there's no statewide law. Huntsville amended its zoning in June 2024 to allow ADUs in R-1, R-1A, and R-1B districts (detached units typically up to 800 sq ft, with no owner-occupancy requirement). Birmingham permits ADUs up to 1,200 sq ft or 50% of the main home, though not yet in all residential districts, and is working on a clearer ordinance. Confirm your specific city/county.
Wind and flood. Mobile and Baldwin counties carry high coastal design wind speeds, and FEMA flood zones require elevating to base flood (typically pilings). These are factory-order decisions — the unit must be engineered to the coastal wind and elevated, or it won't be insurable. PSL Modular configures both for coastal Alabama.
General information, current as of 2026 — not legal advice. Confirm specifics with your local jurisdiction.
Inland (Birmingham, Huntsville, Montgomery) the drivers are tornado/high wind and summer heat — a robust structure and an efficient thermal envelope. There's effectively no snow. Seismic is generally low. PSL Modular sets the envelope from your site.
Yes on both. Huntsville's aerospace/defense boom drives strong housing and ADU demand (and its 2024 zoning change helps), while the Gulf Coast is a rental market that rewards fast, coastal-rated construction. The AMHC-approved unit clears the building; your work is local zoning and (on the coast) wind/flood.