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Renovating a Home in Marin: Design Review and Permits by Town

By Matthew Martinez, Founder, CEO & Managing Broker, Diamond Real Estate Group. California DRE #01869679.

Most exterior renovations in Marin need a design review approval before the building department will issue a permit, and the agency that grants it depends on where the house sits: one of the county’s cities or towns, or unincorporated Marin, where the County of Marin decides. Each jurisdiction sets its own triggers, exemptions, notice rules and expiration dates. Near the ocean or Tomales Bay, a coastal permit can be needed as well.

This guide is for buyers who are pricing a house on what it could become and for owners planning a remodel before they sell. It explains how to find the right agency, what the County’s code exempts, how review works in Belvedere, Tiburon, Ross, Mill Valley, San Anselmo and Larkspur, what story poles and neighbor notices involve, and what unapproved work means when the house goes on the market. For how design review shapes prices at the top of the market, see our Marin luxury homes guide.

Step one: find the agency that reviews your house

A Mill Valley or San Rafael mailing address doesn’t prove the parcel is inside that city. Unincorporated places such as Kentfield, Tamalpais Valley and most of West Marin are reviewed by the County’s Community Development Agency. Check the assessor’s parcel record or call the planning counter with the parcel number before you read any code.

Confirm the jurisdiction from the parcel number: city, town or unincorporated County.
Check for the Coastal Zone. In unincorporated West Marin, coastal permitting runs alongside or instead of ordinary design review.
Pull the planning file. Ask for past design review approvals, conditions of approval, variances and any open code enforcement case.
Pull the building permit history and match each addition, deck and outbuilding to a permit with a final inspection.
Read the current code section for your district, then book a pre-application meeting with planning staff if the project is significant.

Our Marin access and improvement worksheet covers the physical side of the same question: whether the lot, driveway and site can support the change you have in mind.

Unincorporated Marin: what the County reviews and what it exempts

Chapter 22.42 of the Marin County Code governs design review in unincorporated areas. In conventional zoning districts, review applies to residential projects that would push a lot past 3,500 square feet of floor area, take a main building above 30 feet, or put a detached accessory structure above 16 feet. In planned districts, which cover much of the hillside land, it applies far more broadly.

Section 22.42.025 lists exemptions. The ones homeowners use most:

Small additions in planned districts: a one-story addition or detached accessory structure that adds no more than 750 square feet or 20% of the existing floor area, whichever is less, keeps the total at 3,500 square feet or less and meets the height and setback tables.
Decks up to five feet above grade with at least five-foot setbacks, and attached porches with setbacks of at least 10 feet, in planned districts.
Pools and spas no more than 30 inches above grade, set back at least 10 feet.
New and replacement doors, windows and skylights in planned districts.
Replacement of existing retaining walls in any district.
Accessory dwelling units that meet the County’s ADU standards.
Repair or in-kind reconstruction of legally established structures.

One condition matters to buyers. The small-addition exemption is unavailable if work previously approved through design review never received a final building inspection. An unfinished permit from a prior owner can therefore push a modest addition into full review.

When review is required, the Community Development Agency Director decides most applications, the Zoning Administrator acts when a public hearing is required, and the Director can send significant policy questions to the Planning Commission. Notice follows the County’s general noticing chapter, and approval depends on findings that include protecting neighbors’ sun, primary views and privacy.

Coastal Zone homes: a second permit layer

The County says most development in the coastal zone needs a Coastal Permit. The Coastal Commission has granted Marin categorical exclusions for some projects in mapped areas, but even an excluded project needs a County Coastal Permit Exclusion before building, septic or well permits are issued.

For example, an exclusion order covering Point Reyes Station allows minor residential additions of no more than 50% of the existing floor area or 1,000 square feet, whichever is less. It doesn’t apply to a structure built before 1930, to homes inside the historic area boundaries of Tomales, Marshall, Point Reyes Station, Olema, Inverness, Bolinas or Stinson Beach, or to tidelands, beaches and similar areas.

Coastal permit exemptions for single-family improvements, and the bluff, septic and shoreline exceptions to them, are explained in our post on buying coastal property in Sonoma and Marin. Shoreline homes on the bay side face a different set of agencies, covered in our Marin waterfront homes guide.

How the towns compare

Cities and towns write their own design review chapters. The table summarizes the parts that most often change a remodel budget or schedule; town-by-town notes follow.

Jurisdiction	Who decides most residential projects	Neighbor notice and story poles	How long an approval lasts
Belvedere	Planning Commission; staff for small exceptions	Check with the city	See code section 20.04.060
Tiburon	Design Review Board; director for minor alterations	Courtesy notice within 300 feet; story poles for minor alterations that materially raise roof height or mass, up before notices go out	Three years unless a building permit issues; no extensions
Ross	Town Council at a public meeting	Written notice at least 10 calendar days before the hearing	Not confirmed
Mill Valley	Zoning Administrator, or Planning Commission for new units and significant issues	Hearing notice under the city’s general noticing rules	One year, with up to two one-year extensions on request
San Anselmo	Planning Director for minor changes and residential additions unless the code requires the Planning Commission; Commission for other exterior work and floor area exceptions	Director may require story poles; hearing notice rules are in a separate article we didn’t review	Not confirmed
Larkspur	Zoning Administrator or Planning Commission, under sections 18.64.025 and 18.64.030 (not reviewed)	Section 18.64.035 (not reviewed)	Section 18.64.090 (not reviewed)
Unincorporated County	CDA Director, or Zoning Administrator when a hearing is required	Under the County’s noticing chapter	Check with the County

“Check with” and “not confirmed” mean we couldn’t read the rule in the code text available to us. They are not statements that no rule exists. We did not review the design review rules of Sausalito, Corte Madera, Fairfax, Novato or San Rafael for this guide, so ask those planning departments directly.

Belvedere

Belvedere’s design review chapter reaches well beyond additions, with its own standards for fences and screening, exterior lighting and skylights, drives and parking, privacy and landscape plans, and the Planning Commission is its review body. See our Belvedere page for the city’s other rules. The chapter is also unusually explicit about work done without approval: permits issued in conflict with it are void, unapproved work is declared unlawful and a public nuisance, and each day a violation continues is a separate violation.

An owner can apply for retroactive design review, but if the Planning Commission finds that the applicant intentionally built without approval, it may deny the application on that ground alone, and staff then schedule a City Council hearing on abatement. For a buyer, that makes Belvedere’s planning file one of the first documents to read.

Tiburon

In Tiburon, a building permit for an exterior alteration, a pool, an HVAC unit or generator, a new driveway or grading over 50 cubic yards all route through site plan and architectural review. The director can decide residential additions and accessory buildings under 500 square feet; larger work goes to the Design Review Board.

Tiburon’s approvals are time-limited: one lapses three years after approval unless a building permit has been issued, and the code allows no time extensions. A director’s decision on a minor alteration must be appealed within five business days. A buyer relying on a seller’s approved plans should confirm the approval date before closing.

Ross

The Ross Town Council itself conducts design review and decides applications at a public meeting, with written notice at least ten calendar days before the hearing. Some work is exempt from design review altogether, including repainting with no exterior remodeling, accessory dwelling units under the town’s ADU chapter, and attic and basement improvements under their own chapters, unless the work is within 25 feet of a creek or tied to a project that needs review. Ross’s thresholds, guideline floor area and creek setbacks are summarized on our Ross page.

Mill Valley

Mill Valley’s chapter applies to new structures and to changes of use of 150 square feet or more, as well as additions and exterior changes, whether or not a building permit is needed. Most single-family work is exempt below the city’s size and demolition thresholds. Two details catch people out: parcels on East Blithedale Avenue or in the RP, RSP and RMP districts lose the exemption, and projects started within 24 months of a prior project’s final inspection are added together when the thresholds are applied.

A Mill Valley approval expires one year after it takes effect unless the approval says otherwise; the owner can ask for a one-year extension before it lapses, and up to two can be granted. More on the city’s hillside and canyon lots is on our Mill Valley page.

San Anselmo

San Anselmo splits its residential rules by elevation. On hillside lots in the R-1-C and R-1 districts at or above 150 feet above sea level, design review covers new houses, second-story additions, additions over 500 square feet counted cumulatively from February 26, 1991, and requests to exceed the maximum dwelling size. On flatland lots below that line, it covers new houses, second-story additions, additions that raise adjusted floor area by 50% or more, additions combined with demolishing half or more of the exterior walls, and requests to exceed the maximum adjusted floor area.

Additions built between five and eight feet from an interior side property line also need review. The Planning Director handles minor changes such as windows, doors, awnings and color, and residential additions unless Commission review is required, and can ask for story poles. The findings ask whether a project unreasonably impairs neighbors’ light and air or privacy, including through windows, skylights and decks. See our San Anselmo page for the town’s other rules.

Larkspur

Larkspur’s chapter applies to work that needs a building permit or a discretionary permit, then exempts several common residential projects if they meet district standards and need no other discretionary approval: a new single-story house or duplex, or a ground-level single-story addition, no more than 20 feet above grade; accessory structures of 400 square feet or less; roof-mounted solar panels no more than three feet above the roofline; ADUs unless the ADU chapter requires review; and repair or reconstruction of nonconforming structures under the city’s nonconforming-structures chapter.

A second-story addition, or anything taller than 20 feet, falls outside those single-story exemptions. Larkspur also has separate chapters on residential floor area ratios and on slope and hillside development, so a hillside remodel can trigger more than one set of standards. More on the city is on our Larkspur page.

Story poles, notices and the neighbors

Story poles are temporary frames, usually wood or metal posts with tape or netting, that outline the height and footprint of a proposed addition so neighbors and decision-makers can see its effect before a hearing. Where a town requires them, as Tiburon does for minor alterations that materially raise a roof or add visual mass, the poles go up before notices are mailed, so they add days to the schedule and a cost to the budget.

Notice is what turns a design into a neighborhood conversation. Tiburon mails courtesy notices to owners within 300 feet, Ross sends written notice ten days before the council hearing, and the County notices administrative decisions and hearings under its general rules. In view areas, expect comments about views, privacy and light, because the County’s findings and Tiburon’s criteria name them directly. Tree-blocked views are a separate legal question, covered in our post on Marin view ordinances.

Practical steps that reduce friction: talk to adjacent owners before you file, show them the plans, and adjust what you can before the poles go up.

Buying a house you plan to renovate

An offer premised on expansion should be backed by evidence collected during escrow, not by a listing description that says a house “could be expanded.”

Planning file and permit history. Confirm every prior approval was built and finaled, and read the conditions attached to it.
Floor area already used. Have an architect measure existing floor area the way the town’s code defines it.
Open approvals. If the seller has approved plans, check the expiration date and whether the approval can be used by a new owner.
Site constraints. Slope, creek setbacks, septic capacity and fire access can limit a project more than design review does; our Marin septic systems guide covers the wastewater side.
Schedule and cost. Ask planning staff how long recent comparable applications took, and build the review period into your holding costs.

Diamond may refer you to partners we work with; you’re free to choose any provider. That includes architects, surveyors and permit expediters.

Unpermitted work when you sell

Several Marin towns compare their permit records with the house at sale. As our selling requirements page details, Mill Valley, Ross, Tiburon, Belvedere, Sausalito, Corte Madera and San Rafael each require a building-records or resale report, so an unpermitted deck or converted garage tends to surface whether or not the seller mentions it. Our page on Marin selling requirements lists each town’s report.

Sellers have three options for unapproved work: legalize it before listing, which can mean retroactive design review as well as a building permit; remove it; or disclose it and price it. Whatever you choose, disclose what you know. Our California seller disclosures guide explains the forms, and selling a home with an unpermitted ADU covers the most common case.

Questions people ask

Do I need design review to remodel a house in unincorporated Marin?

Often, but not always. In conventional districts, review is triggered by size and height thresholds, and in planned districts it applies more broadly. Section 22.42.025 exempts small additions, low decks, low pools, door and window changes, in-kind repairs and qualifying ADUs.

How long does a Tiburon design review approval last?

Three years from approval unless a building permit has been issued or, where none is needed, the work is complete. Tiburon’s code allows no time extensions.

When does a Mill Valley addition need design review?

When it reaches 35% of the existing gross floor area or 1,000 square feet, demolishes half or more of the exterior, or is on East Blithedale Avenue or in the RP, RSP or RMP districts. Projects within 24 months of a prior final inspection are counted together.

Who approves design review in Ross?

The Town Council, at a public meeting with written notice at least ten calendar days before the hearing. Repainting, ADUs and some attic and basement work are exempt.

Do I need a coastal permit to add on to a house in West Marin?

Usually you need either a Coastal Permit or a County Coastal Permit Exclusion. Exclusions are limited to mapped areas and criteria, and they don’t cover pre-1930 structures or homes in the historic areas of the coastal villages.

What are story poles?

Temporary poles and tape outlining a proposed addition’s height and footprint, put up before a design review decision so neighbors can see the change. Tiburon requires them for minor alterations that materially raise roof height or mass.

Can I get approval for work a previous owner built without permits?

Often you can apply after the fact. Belvedere, for example, offers retroactive design review but may deny an application if the work was built intentionally without approval. Expect to need a building permit and inspections too.

Does an approved design review transfer to a buyer?

Don’t assume it does. Each approval has conditions and an expiration date, such as Tiburon’s three years or Mill Valley’s one year, so ask the planning department in writing whether the approval is still valid and whether a new owner can build under it.

This guide summarizes local codes for planning purposes; it is not legal advice. Before you buy on the strength of a renovation plan, confirm the rules with the planning department and, for anything contested, a California land-use attorney.

If you’re weighing a Marin house for its potential, or preparing one for sale, talk with Diamond about Marin County and we’ll help you line up the records before you commit.

Sources & notes

GoCodebook copies are unofficial reproductions of each code; confirm current text with the planning department before relying on it. Sausalito, Corte Madera, Fairfax, Novato and San Rafael rules were not reviewed for this page.

Last reviewed October 2026 by Matthew Martinez.