In Ross, design review is king — except for ADUs. An ADU contractor explains.

Everything about building in Ross usually runs through the town’s Advisory Design Review process — except a conforming ADU, which the code requires Planning to approve or deny ministerially, in writing, within 60 days of a complete application, with no hearing and no public notice. A denial has to come with a complete list of deficiencies and how to fix them. For a town this careful about its streetscape, that’s a remarkably clean path.

What Ross has instead of design review is a set of objective standards written into the ADU chapter, and they’re worth designing to from day one. Windows facing a neighboring property within 15 feet of the line must be clerestory, with sills at least six and a half feet above the floor. Exterior lighting must be shielded, aimed down, and no cooler than 3500K — Ross is serious about dark skies. And any tree over 12 inches in circumference removed for ADU construction gets replaced on site with a 24-inch box tree. None of this is discretionary; all of it is checkable on plans, which is the point.

Applications go through the Building and Planning Department at Ross Town Hall, 31 Sir Francis Drake Boulevard, where the counter runs weekday mornings, Monday through Thursday. The town publishes an ADU checklist and takes submittals by email — small-town process, in the best and slowest senses. Complete, well-organized submittals matter even more here than in bigger cities, because there’s no large staff to shepherd a messy one.

The by-right sizes are 850 square feet for a one-bedroom or studio and 1,000 square feet for anything larger, with a guarantee that no lot standard — floor area, coverage, minimum lot size — can stop an 800-square-foot ADU with four-foot side and rear setbacks. A junior ADU inside the house runs up to 500 square feet. Detached units cap at 16 feet of height, or 18 within a half-mile walk of major transit plus two feet to match the main home’s roof pitch; attached ADUs can reach 25 feet.

Everything beyond that box goes to the Town Council — literally. Ross has no zoning administrator hearing for ADU exceptions; more height, more than 1,000 square feet, or a second detached unit on a big lot means a public hearing before the elected council, with findings on views, privacy, and light, an engineered drainage design showing no net increase in runoff, and the fire chief confirming adequate firefighting water supply. An ADU over 1,000 square feet additionally requires recording a 20-year rent restriction reserving the unit for a very-low-income household.

Our honest advice, having watched how discretionary review goes in small Marin towns: design inside the ministerial box. The difference between a 1,000-square-foot ADU approved on paper in 60 days and a 1,100-square-foot ADU debated at a council hearing is not 100 square feet — it’s a different project, on a different timeline, with a different risk profile.

Ross’s large lots hold generations of accessory buildings — carriage houses, guest cottages, studios, barns — and conversions are where the town’s ADU math gets genuinely good. An ADU converted from an existing structure needs no setbacks at all, can expand up to 150 square feet to handle entry and egress, requires no replacement parking even if it was a garage, and pays no sewer or water capacity charges. On a valuation-based fee schedule, starting from an existing shell also keeps the permit fees themselves down.

The code holds two more unusual cards. First, the council may allow floor area converted to ADU space to be transferred back to the lot as an allowance for a future addition to the main house — converted square footage isn’t necessarily lost to the property’s development budget. Second, there’s amnesty: the town can’t deny an ADU permit for a unit built without permits before January 1, 2018 on the basis of building-standard or zoning violations, absent a genuine health-and-safety problem. If your property came with a quietly-converted cottage, there’s a legalization path.

Ross floods. Corte Madera and Ross creeks run through the flats, the town has taken three 100-year storms since 1982, and floodplain compliance is written directly into the ADU chapter — an ADU in the mapped flood plain must meet the town’s flood damage prevention code. The town sells a flood-zone determination letter, and checking the FEMA map is one of the first things we’d do on any flats parcel.

Above the flats, Ross is wooded hillside, and fire rules come from the Ross Valley Fire Department — the same agency that reviews our San Anselmo projects. Ross has adopted the 2025 California Fire Code and Wildland-Urban Interface Code with local amendments, and parcel-level WUI status is checked on RVFD’s map. The code mirrors state law on sprinklers — an ADU doesn’t need them if the primary home doesn’t — but for brand-new detached construction we confirm the trigger with RVFD in writing rather than assume. Trees round out the site picture: removals need permits, and the ADU chapter’s replace-with-a-24-inch-box rule applies on top.

On fees, the numbers are current as of the schedule that took effect July 1, 2026: $1,204 for ADU administrative review, a valuation-based building permit fee with plan check at 70% on top, and a 10.46% general plan surcharge. The town’s drainage and road impact fees are each 1% of valuation — though state law bars impact fees on ADUs under 750 square feet, which we confirm in application with town staff. Sewer is Ross Valley Sanitary District: a $513 ADU permit, no capacity charge for conversions, and $335 per fixture unit for new construction. Water is Marin Water, where detached units pay $507 per fixture unit and conversions within existing space pay no capacity charge. School fees are set separately by the districts and don’t apply below 500 square feet.