How Long Does It Take to Build an ADU in the Bay Area?

The most common ADU timeline question is "how long until we can rent it out?" The honest answer is 9–14 months for a detached new-construction ADU in the Bay Area — and the construction phase isn't usually the bottleneck. Here's the realistic month-by-month breakdown.

Phase 1 — Design and engineering (8–14 weeks)

• Initial site visit and feasibility (1 week)
• Schematic design and selection (3–4 weeks)
• Construction drawings (3–5 weeks)
• Structural engineering (concurrent, 2–3 weeks)
• Title 24 energy calcs (1–2 weeks)

If your city requires a soils report (most Bay Area cities do for new construction), add 2–3 weeks. Hillside lots can add another 2–4 weeks for additional geotechnical work.

Phase 2 — Permits (8–16 weeks)

This is where ADU timelines surprise homeowners. Even with the state's ADU streamlining laws:

• First plan check round: 4–8 weeks (varies by city)
• Revisions and resubmittal: 2–4 weeks
• Second plan check round: 2–4 weeks
• Permit issuance: 1–2 weeks

Cities like San Mateo, Mountain View, and Sunnyvale tend to be faster. Palo Alto, San Francisco, and Burlingame's design review districts run slower.

Phase 3 — Construction (varies by ADU type)

Detached new-construction (5–7 months)

• Site prep and foundation: 4–5 weeks
• Framing and sheathing: 3–4 weeks
• MEP rough-in: 3–4 weeks
• Insulation, drywall, exterior: 4–5 weeks
• Finishes (cabinets, tile, flooring, paint): 6–8 weeks
• Final inspections and certificate of occupancy: 1–2 weeks

Attached ADU / addition (4–6 months)

Slightly faster than detached because you skip some site work, but the tie-in to the existing structure can introduce surprises.

Garage conversion (3–4 months)

• Slab evaluation and prep: 1 week
• Framing modifications (egress windows, interior walls): 2–3 weeks
• MEP rough-in: 2–3 weeks
• Insulation, drywall: 2 weeks
• Finishes: 4–6 weeks
• Inspections: 1 week

What can extend the timeline

• Utility upgrades. If PG&E needs to upgrade your service, that's their schedule, not yours. Allow 2–6 months.
• Sewer lateral. Some cities require sewer lateral replacement when an ADU is added. Add 2–4 weeks.
• Tree protection. If your site has protected trees, plan reviews can add 4–8 weeks.
• Material lead times. Custom cabinets and certain windows can be 12–16 weeks out.

What can compress it

• Pre-approved ADU plans (offered by some cities, cuts plan check)
• Standardized cabinet packages instead of custom
• Garage conversion path (skips foundation + framing)
• Working with a design-build contractor (parallel design + permits + construction prep)

See a recent ADU we completed in San Mateo, or learn more about our ADU construction services.