Mill Valley Zoning, Planning & Building Codes

Last reviewed: July 3, 2026

Overview

Mill Valley’s land-use regulations are codified in Title 20 (Zoning) of the Mill Valley Municipal Code and organized by district chapters, objective development standards, design-review rules and a set of housing and overlay chapters that layer modified standards on base zones. The code divides the city into residential, commercial, open-area and several overlay districts and places major technical standards (setbacks, heights, FAR, parking) in dedicated sections so readers can find the rule that controls a project. For specifics on permit pathways, design review and ministerial vs discretionary approvals see the applicable chapters cited below; each statement here is tied to the controlling Mill Valley code provision.

How Mill Valley's code is organized

• Title 20 is structured as a set of topic- and district-specific chapters rather than one long table of rules. General district definitions and the official list of district families appear under § 20.12.010 – § 20.12.040 (districts generally). The zoning map (on file with the Planning Department) implements those district labels.
• Base zone chapters (for example, the RS single-family chapter, the RM multi‑family chapter, C‑G general commercial chapter, etc.) contain permitted uses and district‑specific numeric standards (see the RS and RM chapters cited below). See the RS and RM chapters for the district‑by‑district development rules.
• Citywide technical rules—including lot‑coverage and FAR calculations, parking requirements, setback exceptions and many accessory‑building rules—are implemented in dedicated chapters such as the floor‑area rules at § 20.48.010, the parking rules at § 20.60.090, and the general development exceptions at § 20.60.060 – § 20.60.070.
• Design review is a stand‑alone permitting layer: the City’s design‑review rules, exemptions and required findings are in Chapter § 20.66 (see exemptions at § 20.66.030 and findings/limitations at § 20.66.045).
• Housing‑focused overlay districts and recent housing tools are in their own chapters (housing overlays and small‑lot / opportunity‑site overlays), which modify or supersede base zone standards where expressly written. The code instructs that qualifying projects may use state tools (density bonus) for objective standard modifications.

Practical navigation tip: start with the base zone chapter (e.g., RS = single‑family, RM = multi‑family, C‑G/C‑N/C‑R = commercial) to find use rules, then read the cross‑cutting chapters for FAR (§ 20.48.010), parking (§ 20.60.090) and design review (Chapter 20.66) that will apply to most permit applications.

Zoning district families

Mill Valley’s code explicitly categorizes districts; the list is in § 20.12.010 – § 20.12.040. The principal families are:

• Residential: RS (single‑family residential), RM (multiple‑family residential), DR (downtown residential), R‑P (residential planned) — see the RS chapter for the single‑family numeric standards and the RM chapter for multi‑family standards.
  • Example numeric rules in the RS family include a standard max building height of 25 ft for dwellings (with some 35 ft exceptions) and 15 ft exterior setbacks; minimum interior setbacks are 1 ft per 1,000 sq ft of lot area (but no less than 5 ft and no more than 15 ft) — see § 20.16.040 for the RS development table and related text.
  • In the RM family the RM‑3.5 district sets min land area per dwelling = 3,500 sq ft, max lot coverage = 50%, and exterior setback = 15 ft as examples of district‑level numeric standards; consult § 20.24.030 for the RM use table and standards.
• Commercial: C‑G (general commercial), C‑R (commercial‑recreation), C‑F (community facilities), C‑N (neighborhood commercial), plus downtown character subareas (C‑D, C‑L, etc.). Each commercial chapter explains permitted uses and downtown/commercial area character rules (see § 20.40.010 – § 20.40.060).
• Other / special: O‑A (open area), U (unclassified/new annexations), PD (planned development combining), and overlay districts such as H‑O (historic overlay), Office Conversion Housing Overlay, Small Lot Housing Overlay and Opportunity Site Housing Overlay. The district list and overlays are in § 20.12.010 and overlay chapters (see the SLHO provisions).

(Every district chapter contains a uses table and notes; always read the “Additional Standards and Provisions” listed in the use table for that chapter to see cross‑references to parking, design review and other chapters.)

Citywide development standards

Where the code expects consistency across zones the numeric standards are located in dedicated sections so they can be applied to multiple districts.

• Floor area and intensity: see § 20.48.010 for Floor Area Ratio (FAR) rules and how the code treats garage/parking exclusions in FAR calculations. Many zone chapters then tie back to § 20.48.010 for their FAR caps or adjusted FAR rules (for example, downtown and mixed‑use overlays reference § 20.48.010).
• Setbacks and heights: base residential maximum height is 25 ft for dwellings, with 35 ft exceptions in specific circumstances; exterior setbacks = 15 ft, interior setbacks calculated as noted above — see § 20.16.040 (RS standards) and cross‑references to general height definitions at § 20.08.050 and exceptions at § 20.60.060 – § 20.60.070.
• Lot coverage and minimum lot sizes: RS district minimum lot sizes and max coverage are tabulated in the RS rules (for example RS‑6 = 6,000 sq ft min lot, max lot coverage 40%) — see § 20.16.040.
• Parking: the city’s off‑street parking rules are organized in § 20.60.090; many zone chapters simply cross‑reference that section for parking counts and then add project‑specific rules (for example, mixed‑use projects in the OSHO have modified parking standards tied to § 20.60.090). For downtown and mixed‑use projects also check the downtown base standards table in the downtown chapter.
• Accessory structures and garages: accessory‑structure size/height limits and garage setback rules are in Chapter 20.60 (and accessory specifics appear in the RS chapter); for example, accessory structures generally are limited to 500 sq ft and have a 15 ft height cap unless otherwise allowed (see accessory‑structure provisions and garage setback rules).

For a project, start with the district chapter to get the use table and the district numeric box, then read § 20.48.010 (FAR), the relevant subsections of Chapter 20.60 (setbacks/height/exceptions), and § 20.60.090 for parking.

Design review and discretionary controls

• Mill Valley requires design review for most new or exteriorly modified structures and many site improvements; the general design review framework, exemptions and filing requirements are in Chapter 20.66 with exemptions listed at § 20.66.030 and the design‑review findings and discretionary limitation language at § 20.66.045. Design review applications are filed to the Planning Department following the procedures in § 20.66.032.
• The code distinguishes ministerial vs discretionary review: smaller or objective‑standard‑compliant housing overlay applications and some Office Conversion/Opportunity Site projects may be approved ministerially by the Director, while other projects are reviewed by the Planning Commission with public hearings (see the Housing Overlay chapter procedures and § 20.66.032). Appeals and timelines are handled under the appeals and expiration chapters (appeals: Chapter 20.100).

If a site triggers design review, no demolition, exterior alteration or new building work that is subject to design review may begin until design review approval and any appeal periods have expired (see § 20.66.020 and related provisions).

Specific plans, planned development and overlay districts

• Planned and specific‑plan style districts: the code contains a classic planned‑residential scheme—R‑P (R‑P districts) and Planned Residential / Planned Development rules that require a land‑capacity determination, master plan and precise development plan. These are codified in the R‑P chapter § 20.18.010 – § 20.18.110 and the Planned Residential chapter § 20.20.010 – § 20.20.110; minimum PD sizes, required findings and master‑plan content are spelled out in those chapters.
• Housing overlays and small‑lot tools: Mill Valley adds housing capacity through overlay zoning (Office Conversion, Small Lot Housing Overlay / SLHO, Opportunity Site Housing Overlay). The overlay chapters provide objective, sometimes ministerial pathways, specific density/height/FAR brackets (for example the SLHO sets a min 17 DU/acre and max 40 DU/acre and a 40 ft max height in the SLHO), and explicit rules about when the Director vs the Planning Commission approves the application. See the Small Lot Housing Overlay provisions for the numeric SLHO rules.
• Historic overlay and other overlays: the H‑O (historic overlay) and additional overlays appear in the district list; each overlay chapter contains the modified standards and procedures that apply when the overlay is mapped to a parcel (listed at § 20.12.010 and in the overlay chapters).

Building permits & review path (practical)

• Typical path: (1) confirm base zoning and overlay, read the district use table and notes (district chapter), (2) check cross‑cutting rules: FAR (§ 20.48.010), parking (§ 20.60.090), accessory/garage rules (Chapter 20.60), design review (Chapter 20.66), and any overlay objective standards (overlay chapter), (3) confirm whether the proposal is ministerial or requires discretionary review (Housing Overlay rules and Chapter 20.66 tell you which), (4) submit design‑review and building permit materials to the Planning Department and Building Official as required by the filing rules (see § 20.66.032 for design‑review filing and applicable building‑permit cross checks).
• Decision bodies: the Planning Commission typically reviews discretionary land‑use entitlements (use permits, planned development master plans, major design review items); the Zoning Administrator handles certain ministerial design reviews, minor variances, second‑unit variances and other administrative items (see the Zoning Administrator powers and appeal right at the relevant chapter). Appeals go to the Planning Commission and then to the City Council under the appeals chapter (Chapter 20.100).

State housing law in Mill Valley

Mill Valley’s Title 20 implements state housing laws in several ways; the code explicitly cross‑references state law where applicable.

• ADUs / JADUs: accessory dwelling units and junior ADUs are regulated by the local ADU chapter (generally codified at § 20.90 in the Title 20 code). The code includes state‑law‑driven items such as maximum sizes, owner‑occupancy or deed‑restriction requirements, utility‑service letters prior to permits, and reduced setback rules where Government Code § 65852.2 applies. The ADU chapter requires a recorded deed restriction and limits short‑term rentals to stays of 30 days or more for ADU/JADU units. See § 20.90 and related subsections for the detailed ADU requirements.
  • For two‑unit projects created under Government Code § 65852.21 (state two‑unit law), the code has a ministerial review pathway by the Planning Director when objective standards are met; see the two‑unit provisions (chaptered near § 20.91 and cross‑referenced to Title 20 objective standards).
• SB‑9 / lot splits / ministerial small‑lot housing: Mill Valley includes overlay and small‑lot housing chapters that provide objective, expedited (ministerial or streamlined) procedures for particular housing types; the code also instructs that qualifying projects may seek objective concessions under state density‑bonus law and that certain overlay approvals are ministerial where the objective standards are met (see the Housing Overlay chapter and the SLHO text). For SB‑9 specifically, local implementation (ministerial lot‑split and ministerial two‑unit rules) must be checked against the latest state statutes; the zoning text references state laws and provides ministerial paths for qualifying two‑unit and small‑lot projects.
• Density bonus / inclusionary linkage: the code expressly permits use of the State Density Bonus Law to modify objective development standards for qualifying affordable housing projects and contains an inclusionary chapter with deed‑restriction rules. See the Housing Overlay chapter and Chapter 20.80 (inclusionary housing references appear in overlay provisions).

Practical note: when proposing housing that leverages state law (ADU, SB‑9, density bonus), assemble the objective standard checklists and the code‑specified deed restrictions and service‑availability letters required by Mill Valley’s Title 20 (ADU and two‑unit sections).

Information gaps / verify with the City

• This page summarizes the parts of Title 20 that are present in the supplied code excerpts. For very specific drafting questions (e.g., whether a marginal parcel qualifies for an overlay exception, or the precise checklist items for a complex PD master plan), consult the live municipal code on the City of Mill Valley website or contact the Planning Department. Several procedural subsections (appeal timelines, fee schedules, and the most recent ordinance amendments) are maintained as ordinance updates; confirm the effective ordinance numbers in the online code. (If you want, I can pull specific subsection text for any named § on request.)

Source References

• Mill Valley Municipal Code — Title 20 (Zoning): district list and general rules, § 20.12.010 – § 20.12.040.
• RS district development standards and table (minimum lot sizes, setbacks, heights): § 20.16.040 (RS chapter content).
• RM (multi‑family) chapter, use table and RM‑3.5 numeric example: § 20.24.030 and RM chapter text.
• Floor area and FAR rules referenced in zone tables: § 20.48.010 (FAR rules / adjusted FAR).
• Parking standards and cross‑references: § 20.60.090 (off‑street parking).
• Accessory structure, garage and setback rules: Chapter 20.60 accessory provisions.
• Design review chapter, exemptions and findings: Chapter § 20.66 (see § 20.66.030, § 20.66.045, filing at § 20.66.032).
• Planned Residential / R‑P master plan and precise development plan procedures: § 20.18.010 – § 20.18.110 and Planned Residential chapter § 20.20.010 – § 20.20.110.
• Housing overlays (Small Lot Housing Overlay, Office Conversion, Opportunity Site Housing Overlay) and ministerial vs discretionary pathways: overlay chapters and housing overlay provisions.
• Two‑unit project rules and ministerial review references (local implementation of Government Code § 65852.21): two‑unit chapter and related provisions (e.g., ministerial criteria, restrictions and recording requirements).