Tiburon design-reviews nearly everything — except your ADU. An ADU contractor’s guide.

Tiburon’s design review process is famous for a reason — but none of it applies to a conforming ADU. The application goes to the Community Development Department at 1505 Tiburon Boulevard as a building permit, submitted electronically, and the town must decide within 60 days of a complete application. There’s no board, no story poles, and no hearing; owners within 100 feet get a courtesy notice, which is informational, not an invitation to object. One deadline worth putting on the calendar: ADU permits expire 18 months after issuance if the unit hasn’t reached certificate of occupancy, so the construction schedule matters from day one.

In place of design review, the ordinance applies objective standards — the kind a plan checker can verify without judgment calls. The 2022 code required exterior colors and materials matching the main house, tightly limited shielded exterior lighting, restrictions on windows and entries near side and rear property lines, and a creek-bank setback; the state flagged several of the old standards as too subjective, and the 2025 rewrite revised the list. We design to the current standards as Planning applies them — this is precisely the layer where a contractor quoting the old code gets a correction letter.

Two Tiburon-specific practicalities. The town has required side-yard setbacks and height to be verified by a licensed surveyor — a real cost and schedule item, not a formality. And a complete application comes with homework attached: a sewer-capacity letter from your sanitary district, fire district review, and — where the Town Engineer calls for it — a geotechnical report. Assembling those before submittal is what makes the 60-day clock real.

In August 2023, the California Department of Housing and Community Development sent Tiburon a findings letter identifying more than a dozen ways the town’s 2022 ADU ordinance violated state law — a 16-foot height cap applied too broadly, a one-ADU-per-lot limit, an attached-ADU cap tied to half the main home’s size, subjective design standards. In January 2025 the Town Council moved a repeal-and-replace ordinance to bring the chapter into compliance. That’s good news for homeowners: the state-law floors are generous, and they now control.

The steadiest reference point is state law, which sets floors no local ordinance can cut below: an 800-square-foot ADU with four-foot side and rear setbacks on essentially any single-family lot, at 16 feet of height — 18 feet within a half-mile walk of a major transit stop — and attached ADUs up to 25 feet. The town’s current guidance describes 850 to 1,000 square feet depending on lot size and bedroom count, with junior ADUs to 500 square feet inside the house. What we deliberately won’t print as settled: the final 2025 tables for size, height, and the revised design standards. We confirm those with the Planning Division — (415) 435-7390 — at the start of every Tiburon project, and you should too before falling in love with a floor plan.

The Tiburon peninsula looks like one town and permits like three. Belvedere is a separate city with its own planning department and its own ADU rules, even though it shares the fire district and a sanitary district with Tiburon. Strawberry and other unincorporated pockets are Marin County jurisdiction — county ADU rules, county reviewers, and access to the countywide ADU Marin program with its free consultations and pre-approved plans. Tiburon proper, notably, is not an ADU Marin member, so those county resources don’t extend to town addresses.

The utility map is just as split. Three sanitary districts serve different parts of town — Sanitary District No. 5 on much of the peninsula, Richardson Bay Sanitary District toward Strawberry, and Corte Madera’s district on the northern fringe — each with its own connection rules, and your ADU application needs a capacity letter from whichever one covers your parcel. Fire service divides at Trestle Glen Boulevard: Tiburon Fire Protection District to the east, Southern Marin Fire to the west. Before any design conversation, we pin down the parcel’s districts — it changes both the reviewers and the budget.

Tiburon has been a sprinkler town since 1983, when it adopted an ordinance requiring automatic fire sprinklers in new and substantially remodeled buildings. For ADUs, state law adds a limit — sprinklers can’t be required in the ADU if they’re not required in the primary residence — but a brand-new detached unit is new construction, and the fire district reviews every project, so we get its sprinkler determination in writing during design. Tiburon and Belvedere are also the only corner of Marin outside the countywide wildfire authority: the Tiburon Fire Protection District runs its own vegetation management program, adopted the 2025 fire and wildland-urban interface codes effective January 2026, and expects a vegetation management plan with project submittals.

The cost that catches people off guard in Tiburon is sewer capacity. Sanitary District No. 5 charges ADUs $10.98 per square foot as a capacity fee — about $8,200 on a 750-square-foot unit, over $10,000 on a 1,000-square-foot one — and the size of the unit is the only lever. Conversions of existing space are exempt from capacity charges under state law, which quietly makes a garage or guest-room conversion thousands cheaper than the same square footage built new. Water is Marin Water, which prices ADU capacity per plumbing fixture unit — another number we confirm per project, since the district updates its charges each July.

On the town side, permit fees are valuation-based with plan check on top, and the posted planning fee schedule is old enough that we confirm the amounts with the town when we apply rather than quote them here. State law bars impact fees on ADUs under 750 square feet and requires them to be proportional above that; school fees apply only at 500 or more square feet of interior space. And Tiburon’s terrain is Tiburon’s terrain: geotechnical reports where the Town Engineer requires them, grading permits priced by the cubic yard, and — on mapped flood parcels near the water — finished floors a foot above base flood elevation with elevation certificates during construction. None of it is unusual for us; all of it belongs in the budget on day one.