ADU Fees

Below are typical fees associated with building an accessory dwelling unit (ADU). Project-specific scope and permit requirements may warrant additional fees. Some fees will be required up front for application review, others will be assessed later for inspections and permit issuance. Refer to Permit Sonoma Fee Schedules for additional information.

All ADUs

These fees apply to all ADU building permits. Additional fees will apply depending on the type of ADU design (Standard, Stick Built Pre-reviewed, Factory Built, or Manufactured) and overall project scope.

• Site Review.
• Impacts and Mitigation. Impact fees are charged proportionately in relation to the square footage of the primary dwelling unit.
  • Fire Impact Fees – ADUs within the following fire districts are subject to fire impact fees:
    • Sonoma Valley Fire District
    • Sonoma County Fire District
  • Parks Mitigation Fees - ADUs less than 750 square feet in size are exempt from park fees.
  • Traffic Impact Fees - ADUs less than 750 square feet in size are exempt from traffic impact fees.
  • Schools - ADUs greater than 500 square feet in size may be subject to school fees by the applicable school district. Contact your local school district for information and fee payment.

• Water/Sewer Connection Fees. New or separate utility connection, or related connection fee or capacity charge, will not be required for the following types of ADUs:
  • Junior Accessory Dwelling Units
  • Internal conversions of existing space within a primary residence or an accessory structure
• Electrical, Plumbing, and Mechanical Fees.
• Photovoltaic System Fees. See Section 150.1.14 of the California Energy Code for when photovoltaic systems may be required or exempted from your ADU project.

Fees By Type of Design

In addition to fees applied to all ADUs, the following apply by type of ADU:

Standard ADUs

 Applications utilizing custom ADU plans that do not use stock pre-reviewed designs, factory built housing, or manufactured homes will be subject to:

• Residential Plan Check - Standard
• CALGreen Residential Plan Review Accessory Structures - Standard

Stick Built Pre-reviewed ADUs

Applications utilizing stick-built pre-reviewed ADU plans a part of our ADU Ready program will be subject to:

• Pre-reviewed ADU Plan Check - Reduced (2-hour minimum)
• CALGreen Residential Plan Review Accessory Structures – Reduced

*If variations from pre-reviewed ADU plans are proposed, alternative fees and timelines may be applied.

*External additions (e.g. decks) not included in pre-reviewed plans shall have the valuation of site built components included in the calculation of plan review and permit inspection fees.

Factory Built Housing

Applications utilizing Factory Built ADUs in accordance with Policy 4-0-9 or as part of our ADU Ready program will be subject to:

• Factory Built Housing Plan Check - Reduced (2-hour minimum).
• CALGreen Residential Plan Review Accessory Structures - Reduced.

*External additions (e.g. decks) not included in factory built components shall have the valuation of site built components included in the calculation of plan review and permit inspection fees.

Manufactured ADUs

Applications utilizing Factory Built ADUs in accordance with Policy 4-0-10 or as part of our ADU Ready program will be subject to:

• If the application is submitted under stamp and signature of a State-licensed engineer or architect:
  • Plan check fees may apply to the foundation system.
• If the application is submitted with a California Department of Housing and Community Development (HCD) approved Permanent Foundation System:
  • Plan check fees may not be collected for the foundation system.
• CALGreen Residential Plan Review Accessory Structures - Reduced.
• Manufactured Home (Mobile Home) Installation, Recordation, and Filing -

*External additions (e.g. decks) not included in manufactured components shall have the valuation of site built components included in the calculation of plan review and permit inspection fees.