Mill Valley — Zoning

Last reviewed: July 2, 2026

Overview

This page summarizes what Mill Valley’s zoning code (Title 20) actually says about zoning districts, the rules that attach to them, and how to read the map and overlays. It is a practical, parcel‑level reference grounded in the Mill Valley municipal code: how districts are named, where they appear on the City’s official Zoning Map, key dimensional limits (setbacks, heights, lot coverage), and which chapters control use and review. See the checklist and risks section for the most common application traps.

How the code organizes zoning in Mill Valley

The City establishes its districts in § 20.12.010 (districts generally) and ties the legal district boundaries to the official “Zoning Map City of Mill Valley” kept by the Planning Department — the map is part of Title 20 and is controlling where there’s no discrepancy resolution. § 20.12.010

Mill Valley’s base districts (as listed in the code) include Residential (RS, RM, DR, R‑P), Commercial (C‑G, C‑R, C‑F, C‑N, C‑D, C‑L), and other classifications (OA, U, PD and multiple overlay zones including the Housing Overlay Zoning Districts). § 20.12.010

Important cross‑references used through Title 20:

• Development standards and dimensional rules are collected in the district chapters and in the city’s Mill Valley Development Standards (see local sections cited below) § 20.16.040, § 20.24.030, § 20.26.020.
• Design and discretionary review rules live in Chapter 20.66 (design review); see the city’s Mill Valley Design Review page for application guidance. § 20.66.020, § 20.66.045
• Off‑street parking rules are in § 20.60.090; see Mill Valley Parking. § 20.60.090
• Accessory dwelling units are regulated in Chapter 20.90; see local ADU guidance at Mill Valley ADUs and the State ADU law. Chapter 20.90
• Housing overlays and how they interact with base zoning are in Chapter 20.30; see Mill Valley Overlay Districts. § 20.30.005 – § 20.30.035

Below are district‑by‑district breakdowns for the zones you’ll encounter most often in Mill Valley. Each subsection lists the chapter/section that controls the text being summarized.

RS (Single‑Family Residential) — Chapter 20.16 (e.g., § 20.16.010 – § 20.16.050)

Purpose: Preserve single‑family neighborhoods and regulate lot sizes, setbacks, heights and accessory uses; ADUs and two‑unit options are separately addressed. § 20.16.010

Typical permitted uses

• One single‑family dwelling, accessory structures, home occupations, small residential facilities, ADUs (Chapter 20.90). § 20.16.010

Key dimensional/decision‑relevant standards (most found in § 20.16.040):

• Minimum front (exterior) setback: 15 ft (habitable structures). § 20.16.040
• Interior setbacks: 1 ft per 1,000 sq. ft. of lot area (min 5 ft, max 15 ft). § 20.16.040
• Height: base 25 ft for dwellings; may be 35 ft in limited circumstances (see exceptions). § 20.16.040
• Minimum lot sizes and widths vary by RS subzone (examples): RS‑6 = 6,000 sf / 60 ft lot width, max lot coverage 40%; RS‑15 = 15,000 sf / max coverage 35%. § 20.16.040

Where RS applies: citywide single‑family neighborhoods; see the official Zoning Map for parcel‑level classification. § 20.12.010

Practical note: design review is typically required for additions and some accessory structures in RS areas (see Chapter 20.66). § 20.66.020

RM (Multiple‑Family Residential) — Chapter 20.24 (e.g., § 20.24.005 – § 20.24.040)

Purpose: Medium and higher density housing — accommodates duplexes, townhomes, apartments and limited neighborhood‑scale nonresidential uses. § 20.24.005

Typical permitted uses

• Multi‑family dwellings, limited supportive and transitional housing, accessory structures, residential second units (Chapter 20.90). § 20.24.005

Key dimensional standards:

• Example RM‑3.5 (illustrative): min land area per unit 3,500 sq ft, max lot coverage 50%, exterior setback 15 ft, interior setback 1 ft per 1,000 sq ft (min 5 ft, max 10 ft), max height 25 ft at required setbacks, 35 ft where deeper setbacks apply. § 20.24.005

Additional rules: RM chapters include minimum usable open space per unit and stepback/transitional height limits where RM abuts single‑family zones. § 20.24.005

DR (Downtown Residential) — Chapter 20.26 (e.g., § 20.26.005 – § 20.26.030)

Purpose: Higher‑density residential near downtown that blends single‑ and multi‑family types and supports rental housing preservation. § 20.26.005

Typical permitted uses

• Rental multi‑family housing by right; other uses (for‑sale multi‑family, offices, nursing homes, some social uses) are conditional or regulated. § 20.26.030

Key dimensional/decision limits:

• Max lot coverage: 50% for DR multi‑family; FAR for multi‑family commonly 0.60 (can be increased to 0.75 in specific cases). § 20.26.005 – § 20.26.020
• Height: base 25 ft at initial setback; may be increased to 35 ft with a 1:1 stepback above that line. § 20.26.020; § 20.26.040
• Setbacks: typical exterior/front habitable setback 15 ft, garages 18 ft to face. § 20.26.040

Design review: DR projects must meet objective residential design standards and design guidelines; stepback and reduced front setback allowances exist through design review. § 20.26.040; § 20.66.045

R‑P / Planned Residential / PD — Chapter 20.18 and 20.20 (e.g., § 20.18.010, § 20.20.010)

Purpose: Planned development of larger tracts where density, layout and design are governed by a master plan and precise development plan. § 20.18.010; § 20.20.010

Key process points and standards:

• Land capacity determination and master plan required before subdivision/development; minimum PD area often 10 acres unless Planning Commission approves smaller. § 20.18.060; § 20.20.070
• Maximum height commonly capped (planned devs: 30 ft unless specific conditions). § 20.20.070

C‑G (General Commercial), C‑D (Downtown Commercial), C‑N (Neighborhood Commercial), C‑L (Limited Commercial) — Chapter 20.40 / 20.45 / 20.52 / 20.40.030

Purpose: Provide for retail, service, offices, mixed‑use and limited residential above ground floor in some commercial zones. See the Downtown Commercial chapter for downtown specifics. § 20.40.030; § 20.45.010

Typical permitted/conditional uses & controls:

• C‑D downtown: mixed commercial uses, limited by floor area rules; base height 35 ft (can be increased to 38 ft in limited cases for commercial plate heights). § 20.45.010; § 20.48.010
• C‑N/C‑G standards: often no required exterior yard, but where a commercial lot abuts an R district the R district yard applies. Hours, live entertainment, and other conditional uses have special limits (see § 20.64 for CUP procedures). § 20.40.020 – § 20.40.030; § 20.64.045

Parking and service requirements are cross‑referenced to § 20.60.090; see Mill Valley Parking. § 20.60.090

C‑R (Commercial‑Recreation) — Chapter 20.52

Purpose: Resorts, marinas, hotels, recreational facilities; many uses require Planned Unit Development (PUD) review. § 20.52.010 – § 20.52.050

OA (Open Area) and U (Unclassified / newly annexed) — Chapter 20.12 / 20.58

Purpose and rules: OA is managed to preserve open space and environmental values; newly annexed lands are first placed in U until rezoned. The Zoning Map shows which parcels are OA and which are U; uncertain boundary interpretations are resolved by the Planning Commission. § 20.12.010

Housing Overlay Zoning Districts — Chapter 20.30

Purpose: Apply targeted housing overlay rules (Office Conversion, Small Lot, Opportunity Site, etc.) to sites identified in the Housing Element; overlays may modify objective development standards and allow ministerial approvals in specified cases. § 20.30.005 – § 20.30.035

Key interaction rule: The overlay does not reduce underlying district requirements unless expressly provided; when there’s a conflict the overlay provisions applicable to the housing overlay govern. § 20.30.020(C)

Quick reference table — most decision‑relevant standards and allowed uses

(Use the official Zoning Map to confirm which of the above applies to a specific parcel; the map is part of Title 20.) § 20.12.010

Checklist (what an applicant must satisfy for a typical residential or commercial application)

• Verify the parcel’s base zoning on the City’s official Zoning Map (Title 20 map) and note any Housing Overlay or Historic Overlay designations. § 20.12.010
• Confirm permitted vs conditional uses in the district chapter (RS: Chapter 20.16; RM: 20.24; DR: 20.26; C‑D: 20.45). § 20.16.010; § 20.24.005; § 20.26.005; § 20.45.010
• Check dimensional limits: lot coverage, FAR, height and setbacks in the applicable district chapter (e.g., § 20.16.040, § 20.24.030, § 20.26.020). § 20.16.040; § 20.24.030; § 20.26.020
• Calculate parking demand per § 20.60.090 and note any ADU parking exemptions (Chapter 20.90). § 20.60.090; Chapter 20.90
• Determine if design review is required (Chapter 20.66). If so, prepare design materials consistent with the City’s objective standards and the Multi‑Family/Downtown design guidelines. § 20.66.020; § 20.66.045
• Identify overlays (Housing, Historic H‑O, Small Lot, Office Conversion) and read Chapter 20.30 and the overlay text for changed standards. § 20.30.005
• If you plan code departures (setback/height), prepare a variance/use permit application under Chapter 20.64 and be ready to demonstrate required findings. Chapter 20.64
• Confirm whether the lot is affected by special environmental or creek setback rules (e.g., Chapter 20.76 creek setbacks). Chapter 20.76

Risks & Ambiguities

Plain‑English summary

Mill Valley’s zoning (Title 20) assigns each parcel a base district (for example RS‑6, RM‑3.5, DR, C‑D) and the Zoning Map controls the district boundaries; each district chapter lists what’s allowed and the key limits (setbacks, heights, lot coverage, FAR). Overlay zones (Housing Overlays, Historic Overlay) can change how a project is reviewed or relax or tighten objective standards — always check the map and the district chapter, then the overlay chapter, and expect design review in many cases. § 20.12.010, § 20.16.040, § 20.26.020, § 20.30.005, § 20.66.020

Source References

• § 20.12.010 — Districts generally; map and district list.
• Chapter 20.16 (e.g., § 20.16.010 – § 20.16.050) — RS districts: permitted uses, setbacks, lot sizes and RS table (RS‑6, RS‑7.5, etc.). § 20.16.040
• Chapter 20.24 (e.g., § 20.24.005 – § 20.24.040) — RM (multi‑family) standards (RM‑3.5 example).
• Chapter 20.26 (e.g., § 20.26.005 – § 20.26.040) — DR Downtown Residential allowed uses, FAR and stepback rules.
• Chapter 20.18 / 20.20 — R‑P / Planned Residential / Planned Development (master plan/land capacity rules). § 20.18.010; § 20.20.070
• Chapter 20.45 / 20.40 / 20.48 — Downtown Commercial and Mixed‑use development standards. § 20.45.010; § 20.48.010
• Chapter 20.30 — Housing Overlay Zoning Districts and procedures. § 20.30.005 – § 20.30.035
• Chapter 20.66 — Design review procedures and discretionary limits (including § 20.66.020; § 20.66.045).
• § 20.60.090 — Off‑street parking requirements and definitions referenced across districts.
• Chapter 20.90 — Accessory Dwelling Units (ADU) rules, local parking exemptions, JADU rules.
• Nonconforming uses / rebuild thresholds — definitions and replacement rules for nonconforming buildings/uses in Title 20.
• Mill Valley internal resource pages (first mention links used in this page): Mill Valley zoning & planning overview, Mill Valley Development Standards, Mill Valley Parking, Mill Valley Design Review, Mill Valley Overlay Districts, Mill Valley ADUs, California Building Standards Code, Mill Valley Nonconforming Uses, Mill Valley Variances and Exceptions. (These internal links are the City/GoCodebook menu pages referenced for practical next steps.)

If a specific parcel or specific numeric standard (e.g., an odd lot width or a historic overlay transfer) is in question: Verify with the Planning Department and ask them to confirm which date/version of the Zoning Map is controlling and whether any site entitlements (CUPs, variances, or overlay rezones) have been recorded. § 20.12.010

Retrieved passages

• Mill Valley Zoning Code (Section 20.60.060.) High relevance show source text
• Mill Valley Zoning Code (Section 20.66.045.) High relevance show source text
• Mill Valley Zoning Code (Section 20.66.020.) High relevance show source text
• Mill Valley Zoning Code (Section 20.66.045.) High relevance show source text
• Mill Valley Zoning Code (Section 20.64.100.) High relevance show source text
• Mill Valley Zoning Code (§ 5) High relevance show source text
• Mill Valley Zoning Code (§ 6) High relevance show source text
• Mill Valley Zoning Code (section of) High relevance show source text
• Mill Valley Zoning Code (Chapter 20.90.) High relevance show source text
• Mill Valley Zoning Code (Chapter 20.26) High relevance show source text
• Mill Valley Zoning Code (Chapter 20.90.) High relevance show source text
• Mill Valley Zoning Code (Section 20.60.060.) High relevance show source text
• Mill Valley Zoning Code (Section 20.48.010) High relevance show source text
• Mill Valley Zoning Code (Chapter 20.40) High relevance show source text
• Mill Valley Zoning Code (Section 20.26.040) High relevance show source text
• Mill Valley Zoning Code (section of) High relevance show source text
• Mill Valley Zoning Code (chapter shall) High relevance show source text
• Mill Valley Zoning Code (§ 2) Medium relevance show source text
• CBC § 1 (Section 20.18.060) Medium relevance show source text
• Mill Valley Zoning Code (§ 8) Medium relevance show source text
• Mill Valley Zoning Code (§ 2) Medium relevance show source text
• California Building Code Medium relevance show source text
• CBC § 4 (title for) Medium relevance show source text
• Mill Valley Zoning Code (Chapter 20.16) Medium relevance show source text
• Mill Valley Zoning Code (§ 10) Medium relevance show source text
• Mill Valley Zoning Code (chapter shall) Medium relevance show source text
• Mill Valley Zoning Code (section may) Medium relevance show source text
• Mill Valley Zoning Code (Section 20.18.070.) Medium relevance show source text

Cited sections

• **§ 20.12.010** — Districts generally; map and district list. (§ 20.12.010)
• **Chapter 20.16 (e.g., § 20.16.010 – § 20.16.050)** — **RS** districts: permitted uses, setbacks, lot sizes and RS table (RS‑6, RS‑7.5, etc.). **§ 20.16.040** (Chapter 20.16)
• **Chapter 20.24 (e.g., § 20.24.005 – § 20.24.040)** — **RM** (multi‑family) standards (RM‑3.5 example). (Chapter 20.24)
• **Chapter 20.26 (e.g., § 20.26.005 – § 20.26.040)** — **DR** Downtown Residential allowed uses, FAR and stepback rules. (Chapter 20.26)
• **Chapter 20.18 / 20.20** — **R‑P / Planned Residential / Planned Development** (master plan/land capacity rules). **§ 20.18.010; § 20.20.070** (Chapter 20.18)
• **Chapter 20.45 / 20.40 / 20.48** — Downtown Commercial and Mixed‑use development standards. **§ 20.45.010; § 20.48.010** (Chapter 20.45)
• **Chapter 20.30** — Housing Overlay Zoning Districts and procedures. **§ 20.30.005 – § 20.30.035** (Chapter 20.30)
• **Chapter 20.66** — Design review procedures and discretionary limits (including **§ 20.66.020; § 20.66.045**). (Chapter 20.66)
• **§ 20.60.090** — Off‑street parking requirements and definitions referenced across districts. (§ 20.60.090)
• **Chapter 20.90** — Accessory Dwelling Units (ADU) rules, local parking exemptions, JADU rules. (Chapter 20.90)
• **Nonconforming uses / rebuild thresholds** — definitions and replacement rules for nonconforming buildings/uses in Title 20. (Title 20.)
• Mill Valley internal resource pages (first mention links used in this page): Mill Valley zoning & planning overview, Mill Valley Development Standards, Mill Valley Parking, Mill Valley Design Review, Mill Valley Overlay Districts, Mill Valley ADUs, California Building Standards Code, Mill Valley Nonconforming Uses, Mill Valley Variances and Exceptions. (These internal links are the City/GoCodebook menu pages referenced for practical next steps.)
• MillValley_ZoningCode.md

• Official Mill Valley code library