ADU permit cost and fee breakdown in Modesto, California
GetYourPermit’s researched permit-fee range for a detached accessory dwelling unit in Modesto, with category estimates and direct reference links used in our investigation.
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ADU size
California prohibits development impact fees for ADUs of 750 sq ft or less, so the 749 / 750 / 751 steps are worth comparing.
Estimated total
GetYourPermit researched range at 750 sq ft
$5,301 – $10,732
This estimate combines our fee-schedule research and project-planning experience. Actual charges vary by parcel, plans, valuation, utilities, and outside agencies.
Typical planning amount
$7,961
Modeled at the 600 sq ft reference.
Where the money goes
These are fee components within the permit process, not separate approvals.
- Separate planning / zoning fee$200 – $500
Shown only where the City bills Planning or zoning review as a separate fee.
- Building plan check$255 – $765
The Building Division’s review of the drawings; part of the Building Permit process.
- Building permit issuance$2,429 – $2,700
The permit issuance charge; where plan check is bundled, the combined amount is carried here.
- Separate trade permits$0 – $200
Shown separately only where electrical, plumbing, or mechanical permits are billed outside a combination permit.
- School district fees$2,100 – $3,150
Possible school-district developer fees based on current thresholds and scope.
- Utility fees$100 – $2,750
Possible water, sewer, electrical, meter, or capacity-related charges.
- Processing, inspection & records$136 – $545
Fixed processing, inspection, records, and administrative charges.
- Surcharges, taxes & state fees$81 – $122
Percentage surcharges, construction taxes, and State-mandated charges.
The darker segment is the low end of the range; the full bar is the high end.
Published fee references
Building permit issuance
The permit issuance charge; where plan check is bundled, the combined amount is carried here.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| ADU or small-dwelling permit fee up to 1,200 sq. ft. | $2,429 | Flat fee | Building Safety Division Fee Schedule — Fiscal Year 2025-26Location: PDF page 1, Residential Fees, Custom Residential Dwelling including Duplex |
Plan check
Review of your drawings for code compliance.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| Structural plan review when separately assessed | Set by City formula | Formula | Building Safety Division Fee Schedule — Fiscal Year 2025-26Location: PDF page 5, Miscellaneous, Plan Review (Structural), and Division EndnotesConfirms: The expired FY 2025-26 schedule records a $255 hourly structural-review rate for separately assessed service; it is not verified as current. |
Impact fees
Development impact fees. Prohibited for ADUs of 750 sq ft or less.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| Capital Facilities Fee for an ADU under 750 square feet | $0 | Flat fee | City of Modesto Capital Facilities Fees Policies and ProceduresLocation: PDF page 12, Accessory Dwelling Unit row and Table 3 exemption rowConfirms: The adopted City CFF policy marks ADUs under 750 square feet as no charge for this impact-fee layer. |
| Capital Facilities Fee for an ADU of 750 square feet or more | Verify on the City’s official website | Formula | City of Modesto Capital Facilities Fees Policies and ProceduresLocation: PDF page 12, Accessory Dwelling Unit sectionConfirms: The City publishes the proportional CFF method but the reviewed source does not provide a current numeric CFF rate for use in the formula. |
Surcharges, taxes & state fees
Percentage surcharges, construction taxes, and State-mandated charges.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| General Plan Maintenance Recovery | Set by City formula | Formula | Building Safety Division Fee Schedule — Fiscal Year 2025-26Location: PDF page 5, Miscellaneous, General Plan Maintenance RecoveryConfirms: The expired FY 2025-26 City schedule records a $0.55-per-$1,000 recovery charge; it is not verified as current. |
These are estimates, not official fees
Use these figures for early budgeting only. They are not a quote, not a government fee determination, and not legal advice. Actual fees depend on your parcel, your plans, your construction valuation, your utility provider, and the fee schedule in force on the day your permit is issued. Confirm every number with Modesto before you commit money.
City reference pages for verification
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