🏠 Accessory Dwelling Unit (ADU)
A secondary, self-contained living unit on a single-family lot — detached, attached, or conversion of existing space (garage/basement).
Permit requirements for Accessory Dwelling Unit (ADU) differ by state and city. The table below summarizes the rule in each covered state — open a state for full detail, fees, and official sources.
| State | Permit? | Authority | Typical fee | Timeline | Go / No-Go | Key notes |
|---|---|---|---|---|---|---|
| California | Permit required | city | Permit and plan-check fees set by the local jurisdiction; state law limits impact fees on ADUs. Verify with the city building department. | ~3–6 months for full plan review; many cities offer pre-approved plans or over-the-counter review. | Generally allowed | State law (Gov. Code §65852.2) requires cities to approve ADUs ministerially by right in most zones; local design review is limited to objective standards. Local fees, setbacks, and coastal/historic overlays still apply. Exempt: By-right up to 1,200 sq ft (≤800 sq ft for a 1-bedroom unit) under state law. |
| Texas | Permit required | city | Permit and plan-review fees set by the city. Verify with the local building department. | Varies by city; 2–8 weeks. | Restricted | Texas has no statewide ADU mandate; ADUs are allowed only where the local ordinance permits (e.g., Austin, Houston, Dallas). Zoning, size caps, and parking rules apply. Exempt: Allowed only where the local ordinance permits. |
| Florida | Permit required | city | Permit and plan-review fees set by the city. Verify with the local building department. | Varies by city; 2–8 weeks. | Restricted | Florida has no statewide by-right ADU mandate; ADUs are allowed only where the local ordinance permits, with size/setback set by that ordinance. Exempt: Allowed where local zoning permits (e.g., Miami 21, Orlando, Tampa). |
| New York | Permit required | city | Permit and plan-review fees set by the city. Verify with the local building department. | Varies by city; NYC ADU filings may take several weeks. | Restricted | New York has no statewide by-right ADU mandate; ADUs are allowed where local law permits (e.g., the NYC ADU program, Buffalo). Zoning applies. Exempt: Allowed only where the local law permits. |
| Pennsylvania | Permit required | city | Permit fees set by each municipality; Philadelphia adds a $3 city and $4.50 state surcharge per permit plus plan-review fees. No single statewide fee. | Typically ~15 business days for residential alterations (Philadelphia L&I); other PA municipalities vary. | Case by case | ADUs require a building permit plus zoning/use approval. The PA UCC governs construction; local zoning controls whether an ADU is allowed on your lot. Verify with your municipality (e.g., Philadelphia L&I). |
| Illinois | Permit required | city | No flat statewide fee; Chicago calculates fees from construction type, occupancy, square footage, and scope via its online calculator. Other municipalities set their own fees. | — | Case by case | Illinois has no statewide building code; most municipalities use the IRC while Chicago enforces the 2019 Chicago Building Code. ADUs require a building permit plus local zoning approval — Chicago and other cities regulate ADUs through zoning. Verify with your municipality. |
| Ohio | Permit required | city | Columbus minimum permit fee $125; total scales with project valuation and trade permits. Municipal fees vary. | Residential permits ~10 business days (Columbus BZS). | Case by case | Ohio’s Residential Code (based on the 2018 IRC) governs construction; ADUs need a building permit plus local zoning approval. Confirm ADU legality with your city (e.g., Columbus BZS). |
| Georgia | Permit required | city | Atlanta minimum permit cost $150 plus $25 technology fee; total scales with cost of construction. Municipal fees vary. | — | Case by case | Georgia’s mandatory 2024 IRC with Georgia Amendments (eff. Jan 1, 2026) governs construction; ADUs need a building permit plus local zoning approval. Verify with your city (e.g., Atlanta Office of Buildings). |
| North Carolina | Permit required | city | Permit fee based on project valuation; Raleigh uses a published Development Fee Guide / calculator. No single statewide flat fee — verify with the issuing city. | Typically 4–10 weeks (plan review + inspections); Charlotte ADU reviews commonly 50–75 days. | Generally allowed | ADUs are allowed in both Charlotte and Raleigh single-family zones. Owner-occupancy not required in Charlotte. Always confirm zoning, setbacks, and parking with the city planning department. Exempt: Charlotte caps detached ADU at 1,000 heated sq ft or 50% of principal dwelling, whichever is less. |
| Michigan | Permit required | city | Building permit based on project valuation; verify with the city. Detroit issues residential permits in about 5 days. | Typically 5–15 business days; Detroit ~5 days, Grand Rapids 5–10 days for simple projects. | Generally allowed | ADUs are allowed in Michigan subject to local zoning. A building permit and zoning approval are required; some cities cap size and occupant/rental rules. Confirm with Detroit or Grand Rapids planning. Exempt: No state size exemption for an ADU (it is habitable space). |
| New Jersey | Permit required | city | Construction permit based on valuation plus a zoning/land-use fee; verify with the city. | Plan review commonly up to 20 business days for subcode review; zoning first. | Generally allowed | New Jersey permits ADUs subject to local zoning. A UCC construction permit plus zoning approval are required. Jersey City publishes ADU zoning guidance — confirm size, parking, and occupancy rules locally. Exempt: No state size exemption — ADUs are habitable accessory structures. |
| Virginia | Permit required | city | Building permit based on valuation plus a 2% state levy (Virginia Beach); verify with the city. | Residential plan review ~10 business days for new construction; zoning first. | Generally allowed | Virginia law requires localities to allow ADUs in single-family zoning. A USBC building permit and zoning approval are required. Henrico lists ADUs as permit-required. Exempt: No state size exemption — ADUs are habitable accessory structures. |
| Washington | Permit required | city | Valuation-based; Seattle SDCI issue fees scale with project value (no flat state fee). | Seattle pre-approved DADU plans ~2–6 weeks; custom plans longer. | Generally allowed | Washington HB 1337 (2025) mandates ADUs; Seattle also allows two ADUs per lot. Owner-occupancy and extra parking are not required in Seattle. Exempt: Statewide HB 1337 (eff. 2025) allows ≥1 ADU per lot; Seattle allows up to 2 ADUs. |
| Arizona | Permit required | city | Valuation-based; set by the issuing city. | Phoenix ~30–90 days; Tucson ministerial review since the Nov 2024 UDC amendment. | Generally allowed | Arizona has no statewide ADU law. Phoenix and Tucson both allow ADUs by local ordinance; Tucson review is ministerial under state HB 2720. Exempt: Phoenix max 1,000 sq ft; Tucson allows ≥1 ADU per lot (up to 2 on lots with an existing home). |
| Massachusetts | Permit required | city | Valuation-based; set by the issuing city (Boston uses a long-form permit). | Boston: up to ~5 weeks for long-form permit review; longer with zoning relief. | Generally allowed | Massachusetts requires ADUs by right under MGL c. 40A §3A; Boston requires a long-form building permit and zoning review. Exempt: State law (MGL c. 40A §3A) allows ADUs by right on lots with a single-family home. |
| Tennessee | Permit required | city | Valuation-based; Nashville residential fee is $5.00 per $1,000 of valuation. | Nashville DADU review under Metro Code §17.16.250; varies by city. | Generally allowed | Nashville streamlined DADU rules in 2025 (removed alley-access requirement, raised size limits); owner-occupancy is required. Other cities follow state ADU allowances. Exempt: Nashville allows detached ADUs (DADUs) by right in most residential zones (Urban Services District). |
| Indiana | Permit required | city | Building permit fee set by the local building department; zoning/use approval also required. | — | Case by case | ADUs are allowed only where local zoning permits an accessory dwelling unit. A building permit is required for construction. Verify with your city (e.g., Indianapolis BNS or Fort Wayne Community Development). |
| Missouri | Permit required | city | Permit fees set locally by each municipality — verify with the city building department (St. Louis Building Division or KC Permits Division). | Varies by municipality — simple permits often same-day to ~2 weeks; full plan-review permits several weeks. | Case by case | ADUs require a building permit plus zoning/use approval. Missouri has no statewide residential building code, so allowance and rules are set locally (e.g., St. Louis and Kansas City each have their own requirements). Verify with your municipal building department. |
| Maryland | Permit required | city | Building permit fee set by the city; zoning/use approval also required. | — | Case by case | ADUs require a building permit and local zoning approval. Maryland’s MBPS governs construction; local zoning controls whether an ADU is allowed. Verify with Baltimore DHCD or Annapolis Planning & Zoning. |
| Wisconsin | Permit required | city | Permit fees set by each municipality — verify with the local building inspection department (Milwaukee DNS or Madison Building Inspection). | Varies by municipality — simple permits often same-day to ~2 weeks; full plan-review permits several weeks. | Case by case | ADUs require a building permit plus zoning/use approval. Wisconsin’s UDC (SPS 320-325) governs one- and two-family dwellings; local zoning controls whether an ADU is allowed on your lot. Verify with your municipal building inspection department. |