California ADU Rules in 2026: What Peninsula Homeowners Need to Know

Accessory Dwelling Units remain one of the most popular ways Peninsula homeowners are adding space and income potential without moving. Here’s where the rules stand in 2026.

Streamlined approval

California law requires most cities to approve compliant ADU applications ministerially (meaning no discretionary hearings) within a set review window. In practice, this has made ADU permitting significantly more predictable than a standard addition, though local jurisdictions still vary in turnaround time.

Size limits

Detached ADUs are generally allowed up to 1,200 sq ft (smaller lots may cap lower depending on local ordinance), and attached ADUs are typically limited to a percentage of the primary home’s square footage. Junior ADUs (within the existing footprint) have their own, smaller size cap.

Parking

Many Peninsula cities no longer require additional parking for ADUs located within a half-mile of transit, which has made smaller, transit-adjacent lots much more viable for an ADU than they were a few years ago.

Owner-occupancy

Owner-occupancy requirements for ADUs have shifted over the past several years and vary by city and unit type. This is one of the first things worth confirming with your local planning department before design starts.

What this means for your project

Because rules differ by city, the first step on any ADU project is a code review specific to your address, not a general rule of thumb. If you’re considering an ADU in Redwood City, Palo Alto, or elsewhere on the Peninsula, talk to us and we’ll walk you through what’s actually buildable on your lot.