City ADU planning guide

San Anselmo ADU regulations and next steps

Start with the most important planning decisions, then review the detailed city rules below before choosing a detached ADU plan or requesting a property-specific feasibility review.

San Anselmo ADU rules overview

Detailed local requirements vary by property. Use this section as a starting point for setbacks, parking, height, utilities, and approval considerations.

Lot fit

Setbacks and buildable area

Start with rear and side setbacks, lot coverage, access, and where a detached ADU can realistically sit on the property.

Design limits

Size, height, and unit type

Check whether the property is better suited for a detached ADU, attached ADU, garage conversion, or junior ADU.

Approvals

Parking, utilities, and permits

Confirm parking exemptions, utility connection requirements, impact fees, and city review steps before finalizing plans.

California ADU Size Framework:

    • California allows detached ADUs up to 1,200 sq. ft. under the statewide ADU framework (Government Code section 66314). A compliant local ordinance may set a lower maximum, but California law prevents any local maximum from going below 850 sq. ft. for a studio/one-bedroom ADU or 1,000 sq. ft. for an ADU with more than one bedroom. The separate 800-sq.-ft. figure is a protected state-law development-standard pathway, not a universal statewide maximum, and a junior ADU (JADU) is generally limited to 500 sq. ft.

San Anselmo Local Maximum:

  • Local ordinance State detached framework: up to 1,200 sq. ft. | Local ordinance: 850 sq. ft. (1 BR or less); 1,000 sq. ft. (2+ BR); exception may allow up to 1,200 sq. ft.
  • How large can an ADU be in San Anselmo?
    • California allows detached ADUs up to 1,200 sq. ft. under the statewide ADU framework. For San Anselmo, the local ordinance maximum shown on this page must also be considered because California law permits compliant local ordinances to use a lower maximum within statutory limits. The separate 800-sq.-ft. rule is a protected development-standard pathway, not the statewide maximum.

What Makes Building an ADU in San Anselmo Different:

    • San Anselmo's August 2026 information sheet lists 850 sq. ft. for one bedroom or less and 1,000 sq. ft. for more than one bedroom.
    • Municipal Code Section 10-6.305 can allow an exception up to 1,200 sq. ft.
    • The Town uses 4-foot side/rear setbacks for new ADUs and publishes detailed height allowances.
    • Fire access, slope, vegetation management, flood/coastal conditions and septic capacity are often as important as the nominal zoning maximum.

Setbacks, Height and Parking:

    • For qualifying new-construction ADU pathways, 4-foot side and rear setbacks are an important California protection. Height allowances now vary by configuration, transit proximity and whether the ADU is attached or detached. Parking is often exempt under state law, particularly for transit-proximate and conversion projects. Because San Anselmo may have more permissive local standards, the current local ordinance should be checked before fixing the building footprint or height.

Preapproved and Prefab ADU Options:

  • Local preapproval status Preapproved detached ADU resources available through Town/ADU Marin.
    • A preapproved plan and a factory-built/state-approved building system solve different parts of the process. A local preapproved plan can reduce local plan review. A factory-built or state-approved system can move building-system work and inspections offsite. Neither eliminates the parcel-specific review for placement, setbacks, foundation/site work, utilities, grading, fire access and other local conditions.

Permit Strategy for San Anselmo:

    • Start with the property address and confirm jurisdiction, zoning, easements, utility service, fire constraints and any overlay districts. Then determine whether the best project is (1) a locally permitted larger ADU, (2) the state-protected 800-sq.-ft. pathway, (3) an attached/conversion ADU, or (4) an ADU plus JADU or multifamily configuration permitted by current law.

Can I build a 1,200 sq. ft. ADU in San Anselmo?:

  • 850 sq. ft. (1 BR or less); 1,000 sq. ft. (2+ BR); exception may allow up to 1,200 sq. ft.. California's state framework provides for a detached ADU up to 1,200 sq. ft., but the parcel must also satisfy the applicable local ordinance and site standards. The 800-sq.-ft. protected pathway is a separate development-standard protection, not the general maximum.

Do I need a 4-foot setback for an ADU in San Anselmo?:

  • Four-foot side and rear setbacks are protected for important state-law ADU pathways. Conversion ADUs and some local configurations can be treated differently.

Can I use a prefab ADU in San Anselmo?:

  • Generally yes, provided the building system and the parcel-specific site package satisfy applicable state and local requirements.

Does San Anselmo have preapproved ADU plans?:

  • Preapproved detached ADU resources available through Town/ADU Marin.

How long does an ADU permit take?:

  • California law generally requires action on a complete ministerial ADU application within 60 days, but incomplete applications, site-specific agency review and resubmittals can extend total elapsed time.
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Planning an ADU in San Anselmo? Metricon can evaluate the property, identify the maximum practical ADU envelope, compare local and state-law pathways, and coordinate design, engineering, permitting, factory production, site work and installation.

Official / primary source: https://www.townofsananselmo.org/DocumentCenter/View/29466/ADU-and-JADU-Information-Sheet?bidId=

Publishing note: Regulations change. Verify the current ordinance and parcel-specific conditions before quoting a guaranteed size or approval timeline to a homeowner.

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