Home Additions in Millbrae, CA
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Staff Review or Planning Commission
Ground floor vs. second floor: in Millbrae, ground-floor additions are reviewed by staff, usually within about a week, and a fully compliant ground-floor job can often get a building permit within about a month. All non-ground-floor changes need Design Review by the Planning Commission, with a study session, then a public hearing; notice goes to owners within 300 feet, the Commission meets on the first and third Mondays, and there is a 10-day appeal period. Plan on 2 to 3 months to reach approval.
R-1 limits: 55% floor area ratio, 50% lot coverage, 30 feet with a 3:12 or steeper roof (25 feet for flatter roofs), setbacks of 20 feet front, 5 feet sides and 10 feet rear, with upper floors set back another 10 feet at the front and sides. Areas sloped over 30% are excluded from net lot area.
Addition Work
Fees and Utilities
- Additions over 500 sq ft must show school fee receipts from San Mateo Union High School District and Millbrae Elementary School District before permit.
- Fire plans go to Central County Fire, 1399 Rollins Road, Burlingame, with an 8 to 10 business day review.
- In mapped flood zones, improvements over 50% of market value within 5 years count as substantial improvement.
Sewer lateral: added plumbing fixtures or work on 25% or more of the structure starts with an Engineering determination and a video inspection of the sewer lateral.
Before final: a Waste Management Plan final summary showing 65% diversion must be approved before the final inspection can be scheduled. Construction hours: 7:30 a.m. to 7 p.m. weekdays, 8 a.m. to 6 p.m. Saturdays, 9 a.m. to 6 p.m. Sundays and holidays.
621 Magnolia Avenue, Millbrae, CA 94030
Building (650) 259-2330 · Planning (650) 259-2341 · Engineering (650) 259-2339
All building permits go through the City’s online portal (eProcess360); paper applications are not accepted. Inspections are scheduled by email to the Permit Technician or at (650) 259-2330, at least a day ahead. Posted counter and inspection hours vary between City pages, so call ahead.
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Same service nearby: Burlingame · San Bruno · Hillsborough
Millbrae Home Additions FAQ
Does a second-story addition need a hearing in Millbrae?
Yes. All non-ground-floor changes go to Planning Commission Design Review.
How long does second-story approval take?
Typically 2 to 3 months to Planning Commission approval.
What is the floor area limit?
55% floor area ratio in R-1.
Can a ground-floor addition be approved by staff?
Yes, usually within about a week if it complies.