Brentwood, CA Accessory Structures: ADU Impact Fees (2026)

050(J) sets the impact fee rule for accessory dwelling units and junior accessory dwelling units citywide. The city may charge a development impact fee, set by city council resolution under the city's adopted development fee program, but the chapter carves out two exemptions required by state ADU law. First, any ADU under 750 square feet in total floor area is exempt from impact fees altogether, as is any JADU regardless of size, since a JADU is created within the existing footprint of a single-family home.

Second, once an ADU reaches 750 square feet or larger, the city may charge impact fees only in proportion to the square footage of the primary dwelling unit on the lot, rather than the flat per-unit rate applied to a new single-family home. The same subsection separately addresses utility charges: impact fees under paragraph (J)(1) do not include any water or sewer connection fee or capacity charge, which are governed instead by paragraph (J)(2). Under that provision, a conversion ADU on a single-family lot does not need a new or separate utility connection and is not treated as a new residential use for connection-fee purposes unless it is built alongside a brand-new single-family home.

Other ADUs may not simply tap into the primary dwelling's water and sewer lateral except in limited cases (existing connections or a Contra Costa Health Services-approved septic system), and any connection or capacity charge that does apply must be sized proportionally to the ADU's square footage or drainage fixture unit value, not charged as a full new-unit fee.