The same ADU that takes six months to permit in California may take two months in Texas, or be flatly prohibited in a municipality that hasn’t updated its zoning code since 1987. ADU permitting is one of the most state-and-city-specific processes in residential construction.
This guide covers what homeowners need to know before starting the permit process, state by state, in the markets where ADU construction is most active.
What counts as an ADU
An accessory dwelling unit is a secondary housing unit on a single-family or multifamily lot. Types recognized under most state codes:
| Type | Description | Common trigger |
|---|---|---|
| Detached ADU | Separate structure (garage conversion, new build) | Most common |
| Attached ADU | Addition to primary residence | Second most common |
| Junior ADU (JADU) | Conversion within existing house (≤500 sq ft) | California-specific but spreading |
| Above-garage ADU | New unit above an existing attached garage | Common in high-density suburbs |
California
Permitting framework: AB 2221 (2023) and SB 9 require local governments to approve qualifying ADU applications within 60 days. JADU permits are ministerial (no discretionary review) for units within existing footprints.
Size limits: Detached ADUs up to 1,200 sq ft. JADUs ≤ 500 sq ft.
Owner-occupancy requirement: Eliminated for ADUs through 2025 under AB 2221. Check current status, the ban may be reinstated.
Setbacks: Under state law, ADUs within existing structures must be allowed regardless of setback. New construction ADUs have a standard 4-foot rear and side setback under AB 2221.
Typical timeline: LADBS (Los Angeles) runs 3–8 months for full permit. DBI (San Francisco) 3–6 months. Smaller jurisdictions can be faster.
Cost range: $180,000–$350,000 for new detached construction in coastal metros. Garage conversions: $95,000–$175,000 in LA market. $60,000–$120,000 in Sacramento and Inland Empire.
Texas
Permitting framework: Texas preempts local ADU bans on a limited basis; most permitting decisions remain at the municipal level. No statewide ADU-specific legislation comparable to California.
Austin: City Council passed ADU-friendly ordinances in 2023 allowing ADUs by right in most residential zones. Impervious cover limits are the most common constraint.
Dallas/Fort Worth: ADUs permitted in most single-family zones; size limits vary by zoning category.
Houston: No traditional zoning code; deed restrictions and floodplain requirements govern. Harris County’s 500-year floodplain map is the critical overlay.
Typical timeline: Austin 6–12 weeks. Dallas/Fort Worth 8–16 weeks. Houston depends entirely on MUD district.
Cost range: $80,000–$160,000 for detached new build. $50,000–$95,000 for garage conversion.
Washington State
Permitting framework: SB 5235 (2023) requires cities of 10,000+ to allow at least one ADU per single-family lot. Seattle’s DADU (detached accessory dwelling unit) permit process was streamlined in 2019.
Seattle specifics: ADUs allowed by right on most residential lots. Maximum 1,000 sq ft (DADU) or 1,000 sq ft (attached). Separate water and sewer connections required for detached DADUs.
Washington State Energy Code (WSEC): Applies to all ADU construction. WSEC is among the most demanding energy codes in the US, triple-pane windows, balanced ventilation, continuous exterior insulation are common requirements.
Typical timeline: Seattle DCI 3–6 months. Smaller Washington cities 6–14 weeks.
Cost range: $200,000–$380,000 for new detached in Seattle. $100,000–$175,000 for garage conversion with engineering for WSEC compliance.
Oregon
Permitting framework: HB 2001 (2019) and HB 2916 (2021) require cities to allow middle housing and streamline ADU permitting. Portland allows ADUs by right in R2 through R20 zones.
Portland specifics: Detached ADUs up to 800 sq ft or 75% of primary home size (whichever is smaller). System Development Charges (SDCs) for utilities were a major cost barrier; Portland waived SDCs for ADUs until 2024.
Oregon Energy Code: Applies to all ADU construction. All-electric requirements in some jurisdictions under Oregon’s building code path toward electrification.
Typical timeline: Portland Bureau of Development Services (BDS) 2–4 months for simple ADUs.
Cost range: $150,000–$280,000 for new detached in Portland. $80,000–$140,000 for garage conversion.
Colorado
Permitting framework: No statewide ADU mandate as of 2026, but Denver, Boulder, and other major cities allow ADUs by right in most residential zones.
Denver specifics: ADUs allowed in urban single-unit residential zones. Maximum 864 sq ft (detached). Owner-occupancy required. Alley-accessed lots have additional design standards.
Altitude considerations: All ADUs in Denver must account for 5,280-foot altitude in HVAC design. Combustion appliances require altitude-derated BTU specifications.
Typical timeline: Denver Community Planning and Development 8–14 weeks.
Cost range: $120,000–$220,000 for new detached. $65,000–$110,000 for garage conversion.
Florida
Permitting framework: Preemption laws have complicated local ADU ordinances. Florida SB 1604 (2023) requires local governments to allow ADUs in single-family zones, with owner-occupancy restrictions limited to new construction.
Miami-Dade: Impact fees are significant. Hurricane-rated construction standards (Miami-Dade Product Control approval for all windows and doors) apply to all ADU construction.
Orlando: ADUs permitted in most residential zones. Impervious surface coverage is the primary constraint in many subdivisions.
Wind zones: All Florida ADU construction must meet Florida Building Code wind zone requirements, which vary by county and are most stringent in coastal areas.
Typical timeline: 12–20 weeks in major Florida metros including review and wind engineer approval.
Cost range: $90,000–$170,000 for new detached in Tampa/Orlando. $130,000–$220,000 in Miami-Dade with hurricane-rated construction.
What every ADU permit application needs
Regardless of state, most permit applications require:
- Site plan showing setbacks, lot coverage, and impervious area
- Foundation plan, detached ADUs need engineered foundations in most jurisdictions
- Floor plan and exterior elevations
- Structural calculations for new construction
- Energy compliance documentation (Title 24 in CA, WSEC in WA, IECC elsewhere)
- Utility connection plan, water, sewer, electrical
- Egress window dimensions if any sleeping areas below grade
Owner-occupancy rules by state (2026)
| State | Owner-occupancy required? |
|---|---|
| California | No (prohibited through 2025 per AB 2221) |
| Oregon | No (eliminated by HB 2001) |
| Washington | No (SB 5235 bars owner-occupancy requirements) |
| Colorado (Denver) | Yes, owner must occupy primary or ADU |
| Texas (Austin) | No |
| Florida | Varies by municipality |
| Illinois | Varies by municipality |
Always verify current rules, state legislatures and city councils update these regularly.
The permit process, start to finish
- Zoning check, Confirm ADU is permitted on your specific parcel (lot size, zone, deed restrictions)
- Utility capacity check, Water and sewer capacity for a second unit
- Design, Hire a designer or architect familiar with local ADU requirements
- Permit submission, Application, plans, fees
- Plan check, Building department reviews for code compliance (1–12 weeks depending on jurisdiction)
- Permit issuance, Work can begin
- Inspections, Typically 4–8 inspections through construction
- Certificate of Occupancy, ADU is legal to occupy and rent
The firms in our network have active ADU permit history in their local markets. That track record shortens your timeline, contractors who know the plan checkers and have filed dozens of applications move faster than contractors doing their first ADU.