ADU Permitting Guide: Burlingame, San Mateo, Palo Alto & More

California has some of the most permissive ADU laws in the country, and the Peninsula is one of the most active ADU markets in the state. Between aging in place, rental income, multigenerational housing, and Prop 19 estate planning, ADUs are being built on lots that five years ago no one thought qualified.

But every city on the Peninsula interprets state ADU law a little differently. Knowing the state-level baseline — and then knowing where your city adds or restricts — is the difference between a smooth project and an eight-month permit stall. Here's the working knowledge you need.

The state-level baseline (what every city must allow)

As of 2026, California state law guarantees ADU rights on any residential lot, subject to minimum standards. The key points:

• One ADU plus one JADU (junior ADU, inside the primary home) on any single-family lot
• ADUs up to 850 sq ft (studio/one bedroom) or 1,000 sq ft (two bedroom) are permitted by right — cities cannot block them for size
• Setbacks: minimum 4 feet from side and rear property lines
• Maximum height: 16 feet (single story), 18 feet (if near transit or replacing existing structure), 25 feet (for certain two-story ADUs)
• Owner occupancy requirements for new ADUs are waived through 2025 and extended in most cities
• No parking requirement if the property is within a half-mile of transit (applies to most of the Peninsula)
• 60-day ministerial permit review (the city can't deny compliant projects)

This is the floor. Cities can allow more — bigger, taller, less restrictive — but they can't go below it.

City-by-city — Peninsula rules

Burlingame

• Max ADU size: 1,200 sq ft detached; JADUs up to 500 sq ft
• Height: 16 ft single story, up to 18 ft with conditions
• Design review waived for ministerial ADUs
• Typical permit timeline: 10–16 weeks
• Permit fees: variable by jurisdiction
• Utility connection fees: variable; separate water meter not required for most projects

San Mateo

• Max ADU size: 1,200 sq ft detached
• Height: 16 ft baseline, 18 ft with conditions
• Slightly more conservative setback interpretation — pay attention to eaves and overhangs
• Typical permit timeline: 12–20 weeks (longer queue than Burlingame)
• Permit fees: variable by jurisdiction
• Utility fees: varies by neighborhood; some require a sewer capacity study

Hillsborough

• Allows ADUs under state law but with design review where visible from public street
• Max size: 1,200 sq ft
• Setbacks: 5 ft minimum, often larger due to lot sizes
• Height: typically 16 ft; additional restrictions in some overlay zones
• Typical permit timeline: 14–24 weeks due to architectural review
• Permit fees: variable by jurisdiction
• Strong preference for designs that match the primary home's architectural style

Palo Alto

• ADUs widely encouraged; many lots have been converted
• Max size: 1,200 sq ft detached
• Height: 16 ft baseline, exceptions for certain corridors
• Historic district overlays: additional design review in several neighborhoods (Professorville, Downtown North)
• Typical permit timeline: 12–18 weeks for standard; 20–28 weeks in historic districts
• Permit fees: variable by jurisdiction
• Utility fees can be significant — newer Title 24 energy standards may trigger solar requirements

Redwood City

• ADU-friendly; city actively encourages development
• Max size: 1,200 sq ft
• Typical permit timeline: 10–14 weeks
• Permit fees: variable by jurisdiction
• Strong sewer capacity in most neighborhoods

South San Francisco

• Streamlined ADU program
• Max size: 1,200 sq ft
• Typical permit timeline: 8–14 weeks
• Permit fees: variable by jurisdiction
• Lower overall costs than central Peninsula cities

Daly City

• ADU allowed by right, ministerial process
• Max size: 1,200 sq ft
• Typical permit timeline: 10–16 weeks
• Permit fees: variable by jurisdiction
• Steep lots often complicate foundation requirements

San Bruno

• ADU-friendly
• Max size: 1,200 sq ft
• Typical permit timeline: 10–14 weeks
• Permit fees: variable by jurisdiction

Common setback and site issues

Even under permissive state law, your lot has to physically accommodate an ADU. The most common dealbreakers:

• Not enough side or rear yard to fit a 4-ft setback plus the ADU itself
• Easements (utility, drainage, access) that can't be built over
• Large trees with drip lines you can't disturb (especially protected oaks and heritage species)
• Steep slopes requiring expensive foundation work (common in Hillsborough, Daly City, parts of Palo Alto)
• Sewer or water line location — moving these adds significant cost
• Existing detached structures (sheds, studios) that need to be removed

Utility connections

ADU utility connections are often the hidden biggest cost beyond construction itself. Key categories:

• Sewer lateral — new or extended: varies by lot conditions
• Water — connection or new meter: varies (most cities don't require a separate meter for ADUs)
• Electrical — 200A panel upgrade often needed: varies by existing service
• Gas — if adding gas appliances: varies (many ADUs skip gas entirely and go all-electric)
• Internet/cable — homeowner-arranged

ADU types

• Garage conversion — existing shell, but utilities and foundation usually need work
• Attached ADU — built onto the existing home
• Detached ADU — new structure; scope varies significantly by size and finish
• Prefab/manufactured ADU — faster permitting in some cities

Budget varies widely depending on ADU type, lot conditions, finish level, and city. The free consultation is the right place to get a realistic read on your specific scope.

Timeline from day one to move-in

Realistic end-to-end timeline for a detached ADU on the Peninsula:

• Design and engineering: 10–16 weeks
• Permit review: 10–20 weeks (varies by city, can overlap with ordering)
• Construction: 16–28 weeks
• Final inspection and closeout: 2–4 weeks

Total: typically 9–15 months from signing the design agreement to moving in. Garage conversions can be faster (6–10 months total).

Common mistakes to avoid

• Skipping the pre-design site check with a contractor who knows your city. A plan drawn without knowing the sewer location is a plan that gets redrawn
• Underestimating utility connection costs. These can be significant on a Peninsula lot and should be scoped early
• Assuming your lot allows what your neighbor's lot allowed. Two lots on the same street can have different zoning overlays
• Choosing a prefab unit without verifying it meets your city's architectural standards (especially Hillsborough and Palo Alto historic zones)
• Forgetting that ADUs become part of your property tax base (though the increase is typically modest)
• Not planning for rental readiness — a separate address, mailbox, utilities, and sometimes a separate entrance path are required in most cities

Final thought

ADU permitting on the Peninsula is simpler than it was five years ago but still far from uniform. The right starting point is a site walk with someone who's built ADUs in your specific city and knows the current plan-check culture there. From there, you can decide whether your lot, your budget, and your timeline line up.

If you're considering an ADU anywhere from Daly City down to Palo Alto, we've built them in most of these jurisdictions and can tell you quickly whether your scope is realistic. The free consultation is the easiest way to get a real read on your lot.