Millbrae is a fog-belt transit town where BART and Caltrain meet, with a housing stock built largely in the postwar and mid-century decades. The Broadway corridor anchors a modest downtown, the flats carry ranch and split-level homes on rectangular lots, and Millbrae Meadows climbs into the hillside west of the freeway with larger, terraced parcels. Proximity to SFO shapes the local economy — airline employees, airport services, and hospitality workers make up a large share of the tenant pool.
The classic Millbrae ADU play is the garage conversion or the attached addition. The city’s postwar homes almost always include an attached garage on a predictable footprint, making conversion the most economical route — and under state law, it generally cannot be burdened with replacement parking requirements. On the larger hillside parcels in Millbrae Meadows, a detached ADU up to 1,200 square feet is often feasible, with the elevation offering the unit its own outlook and privacy from the main home.
Junior ADUs (JADUs) are a natural fit for Millbrae’s multigenerational households. Carving a compact, up-to-500-square-foot unit out of existing living space gives families a low-cost way to house an aging parent or an adult child under the same roof — no new foundation, no exterior change. State law prohibits cities from requiring owner-occupancy for standard ADUs, so most Millbrae ADU projects can also be rented to long-term tenants without the homeowner living on site.
Millbrae ADU permits route through the city’s Community Development Department, and California’s ministerial (by-right) approval process applies — a compliant project cannot be subjected to discretionary hearings. State law caps required side and rear setbacks at 4 feet. The practical wrinkles come from the housing era and the terrain: mid-century electrical panels are often undersized for a second dwelling, and hillside parcels in the Meadows can need a grading and drainage review. We confirm panel capacity, lateral condition, and slope constraints during feasibility.
Rental demand in Millbrae is deep and transit-fed: the BART and Caltrain interchange, the SFO employment base, and the 101/280 corridors put commuters at the doorstep. Millbrae’s fog-belt microclimate and relative affordability versus the mid-Peninsula keep tenant interest steady. A well-built ADU near the transit stations leases particularly well — and the predictable lot patterns of the postwar neighborhoods make these among the most straightforward ADU builds in the county.
Ready to find out what your Millbrae lot can carry? ADU Cities is a Southern California ADU design-build firm — we handle feasibility, design, permits, and construction under one roof. Call 562.810.1965 for a free consultation and site evaluation. CSLB #1138550.
