Stanislaus County · California
Modesto ADU Fees in 2026
Every government fee we could verify for an ADU in Modesto, from official sources. Figures below are for an 800 sq ft ADU unless noted.
Every figure links to its official source document. Last verified 14 Oct 2026. Fees are re-verified on a rolling schedule (next full pass Dec 2026). Official fee schedule ↗ How we price →
Verified fees, 800 sq ft ADU
$10,494
across 2 line items
The 750 sq ft cliff
$8,065
impact fees at 751 sq ft — $0 at 750 sq ft by state law
Fee table
Amounts computed for an 800 sq ft ADU from each item's published rate. "Exempt" lines are $0 by state law at this size.
| Fee | Category | Rate | 800 sq ft | Source |
|---|---|---|---|---|
| Capital Facilities Fee (ADU >=750 sq ft, proportional to primary dwelling) | Impact fees | flat fee | $8,065 | official doc ↗verified 14 Oct 2026 |
| Building permit + plan check (SMALL RESIDENTIAL UNIT, ADU flat) | Plan check & permits | flat fee | $2,429 | official doc ↗verified 14 Oct 2026 |
These are the line items we have verified so far — not a complete bill. Site-specific charges (utility laterals, soil work) vary by lot. How we price →
The 750 sq ft cliff in Modesto
At 751 sq ft, the impact fees above total $8,065. At 750 sq ft, state law (Gov. Code §66311.5) sets them to $0. One square foot can be worth $8,065 here — size your ADU accordingly.
What changes on January 1, 2027
Two state laws rewrite parts of this table. SB 1117 (Chapter 809) re-bases covered impact fees for up to two ADUs on only the square footage above 750 — at 800 sq ft, most impact-fee lines shrink to a 50 sq ft basis. School developer fees and water/sewer connection or capacity charges are not covered and do not change. AB 956 (Chapter 791) makes two detached ADUs per single-family lot a ministerial approval. Details: SB 1117 and the 750 sq ft cliff · AB 956: two ADUs on one lot
Common questions
Are impact fees waived for ADUs under 750 sq ft in Modesto?
Yes. California law (Gov. Code §66311.5) bars local agencies from charging impact fees on ADUs of 750 square feet or less. That applies in Modesto the same as everywhere else in California. At 751 sq ft, the impact fees we have verified for Modesto total $8,065 — the cliff is real here.
Where do these Modesto ADU fee numbers come from?
Every line item links to the official source document — the city or county fee schedule, the school district's developer-fee resolution, or the utility district's charges — with the date we last verified it. We publish no fee modeled, no fee guessed.
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