ADU permit cost and fee breakdown in Hillsborough, California
GetYourPermit’s researched permit-fee range for a detached accessory dwelling unit in Hillsborough, 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
$12,053 – $20,491
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
$17,290
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$663 – $1,141
Shown only where the City bills Planning or zoning review as a separate fee.
- Building plan check$1,338
The Building Division’s review of the drawings; part of the Building Permit process.
- Building permit issuance$5,352
The permit issuance charge; where plan check is bundled, the combined amount is carried here.
- Separate trade permits$0 – $750
Shown separately only where electrical, plumbing, or mechanical permits are billed outside a combination permit.
- School district fees$2,874 – $3,102
Possible school-district developer fees based on current thresholds and scope.
- Utility fees$350 – $2,750
Possible water, sewer, electrical, meter, or capacity-related charges.
- Processing, inspection & records$150 – $350
Fixed processing, inspection, records, and administrative charges.
- Surcharges, taxes & state fees$1,326 – $5,708
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 Building Permit — New Structure/Construction | $5,352 | Flat fee | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Single Trade & Scope Specific Flat Rate Permit Fees, ADU Building Permit — New Structure/ConstructionConfirms: The FY 2026-27 schedule lists a $5,352 flat fee for an ADU Building Permit for new structure/construction. |
| ADU/JADU Building Permit — Conversion of Existing Space | $3,739 | Flat fee | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Single Trade & Scope Specific Flat Rate Permit Fees, ADU/JADU Building Permit — Conversion of Existing SpaceConfirms: The FY 2026-27 schedule lists a $3,739 flat fee for an ADU/JADU conversion of existing space. |
| Building Permit by Valuation | Set by City formula | Formula | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Building & Combination of Trade Scope Valuation Based Permit Fees, Building Permit by Valuation ($)Confirms: The FY 2026-27 schedule supplies the valuation brackets and rates; the same schedule explains the Town's valuation process. |
Plan check
Review of your drawings for code compliance.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| Plan Check | Set by City formula | Formula | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Building & Combination of Trade Scope Valuation Based Permit Fees, Plan CheckConfirms: The FY 2026-27 schedule distinguishes plan-check percentages by the $1,000,000 valuation threshold. |
Impact fees
Development impact fees. Prohibited for ADUs of 750 sq ft or less.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| Construction Vehicle Impact Fee | 0.83% of valuation | Percent of valuation | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Mandated Fees & Taxes, Construction Vehicle ImpactConfirms: The FY 2026-27 schedule lists the City construction vehicle impact fee as 0.83% of job value. |
| ADU impact-fee rule | Set by City formula | Formula | Ordinance No. 777Location: Ordinance No. 777, 17.52.030, F. Impact FeesConfirms: The Town ordinance sets the under-750-square-foot exemption and proportionality rule but does not establish a single current dollar impact-fee amount. |
Surcharges, taxes & state fees
Percentage surcharges, construction taxes, and State-mandated charges.
| Fee | Amount | Basis | Source |
|---|---|---|---|
| Ministerial ADU Review | Verify on the City’s official website | Estimated range | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Planning Division, Accessory Dwelling Unit (ADU) Review Fees, Ministerial ADU ReviewConfirms: The FY 2026-27 schedule lists $663 for Class 1 State-allowed by-right zoning clearance and $1,141 for Class 2 objective-design/locally regulated clearance; the ordinance distinguishes building-permit-only and ADU planning-permit paths. |
| General Plan Maintenance Fee | 0.61% of valuation | Percent of valuation | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Mandated Fees & Taxes, General Plan MaintenanceConfirms: The FY 2026-27 schedule sets the City General Plan Maintenance Fee at 0.61% of permit valuation and identifies ADUs/JADUs among applicable permit types. |
| Strong Motion Instrumentation Program fee | 0.01% of valuation | Percent of valuation | Appendix A – Schedule of Fees and Charges, Adopted FY 2026-27Location: Building Division, Mandated Fees & Taxes, SMIPConfirms: The FY 2026-27 schedule lists SMIP at 0.01% of permit valuation and describes it as a State fee remitted by the Town. |
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 Hillsborough before you commit money.
City reference pages for verification
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