Impact Fees
Also: development impact fees
Impact fees are one-time charges local governments levy on new construction to fund infrastructure. Under California law, ADUs under 750 square feet are fully exempt from impact fees — which is why many Sacramento owners deliberately size a unit just under that threshold to save thousands to over $20,000.
Above 750 sq ft, impact fees must be charged proportionally to the main house's size, not at a flat rate. The 750 sq ft exemption is the single largest cost lever a homeowner controls. In the Sacramento region this exemption is why so many units land at 749 square feet on paper: crossing into 800 square feet can add thousands to over $20,000 in school, park, and utility-connection fees that an exempt unit avoids entirely. Because the fee above the threshold is proportional rather than flat, a Sacramento owner with a smaller main house pays less on an oversized ADU than one with a large primary home — so the math is worth checking before finalizing square footage.
Go deeper:How much does an ADU cost in Sacramento
Related terms
Back to the ADU glossary.