ADU Construction

Yes. California law requires local cities and counties to review a complete ADU application within 60 days, and most permits are approved in about three to four months. ADUs are allowed on lots with an existing or proposed home in a residential or mixed‑use zone, but you still need zoning clearance, building permits and plan review. BuildRite handles site plans, zoning research and permit paperwork to keep your project moving smoothly.

State law forces local jurisdictions to approve qualifying ADUs even when local rules would otherwise restrict them. Detached or attached ADUs must be allowed up to 800 sq ft, and many cities (San Jose, Oakland, Alameda County, Redwood City) permit up to 1,200 sq ft. All new ADUs need 4‑ft side and rear setbacks; detached units must be allowed at least 16 ft tall, and up to 18‑20 ft when near transit or on multifamily lots. Junior ADUs (JADUs) are created within the existing home and capped at 500 sq ft.

In most Bay‑Area jurisdictions, detached or attached ADUs can be up to 1,200 sq ft, though some cities cap them at 850 or 1,000 sq ft depending on lot size. Detached units must be at least 16 ft tall; attached units can reach 25 ft or match the height of the main house. You must keep 4‑ft side and rear setbacks, and maintain at least 6 ft between structures. JADUs can’t exceed 500 sq ft.

There’s no one‑size‑fits‑all timeline. A typical project—including design, permitting and construction—takes about 10–12 months. Design and permit work may take 2–3 months, while construction generally lasts 6–8 months. Off‑site panelized construction can shorten the build time, but factors like design changes, utility upgrades and city approvals can add several months.

Construction costs vary widely based on size, type and finishes. In 2025, a Bay‑Area ADU generally costs $150,000–$475,000, or $450–$750 per sq ft. Garage conversions tend to be the least expensive (around $80k–$200k) and detached units the most ($200k–$475k). Permit fees and impact fees can add $8,000–$30,000 or more, though units under 750 sq ft often avoid impact fees. BuildRite provides detailed estimates so costs are transparent up front.

Most Bay‑Area ADUs do not require a dedicated parking space. No parking is required when the unit is within a half‑mile of public transit, part of an existing structure, in a historic district, near a car‑share location, or on a lot with restricted permit parking. If you convert a garage or carport, you don’t have to replace the lost parking. All new ADUs must maintain 4‑ft side and rear setbacks, with at least 6 ft between buildings.

For single‑family lots, state law allows one detached or attached ADU plus one JADU. On multifamily lots, property owners can build multiple conversion ADUs (up to 25 % of existing unit count) and up to eight detached ADUs, as long as the total number doesn’t exceed the existing units. BuildRite will verify what’s permissible on your specific lot.