Signed: Two detached ADUs now legal on a single-family lot, fee penalty on larger units cut — both take effect January 1, 2027

On September 29, 2026, Governor Newsom signed two significant accessory dwelling unit bills into law. Together, AB 956 (Quirk-Silva, D-La Palma) and SB 1117 (Cervantes, D-Riverside) make it easier and cheaper to build ADUs on single-family residential lots statewide, effective January 1, 2027 — including throughout Solano County and the greater Bay Area.

AB 956: From one detached ADU to two

Current California law allows a single-family homeowner to build one detached ADU and one junior ADU (JADU) on their lot. A JADU is typically a converted garage or interior space up to 500 sq ft. So the practical maximum today is two units — but only one can be a full, freestanding detached building. AB 956 changes the detached limit to two. Under the new rule, a compliant homeowner could have two full detached ADUs plus the main house — three dwellings on one lot, all eligible for ministerial (streamlined, no-discretionary-review) approval. The bill also voids CC&R and HOA restrictions on ADUs that comply with state law, addressing one of the most common private barriers homeowners face in planned communities.

SB 1117: Cutting the fee penalty on larger ADUs

Impact fees for ADUs are calculated by square footage in many jurisdictions, which creates an asymmetric cost for homeowners building anything larger than a studio. Under current rules, a 900-sq-ft ADU gets charged fees on all 900 square feet. SB 1117 changes the baseline: jurisdictions may only charge impact fees on square footage above 750. For a 900-sq-ft ADU, that means fees on 150 square feet rather than 900 — a meaningful reduction for anyone building a full one-bedroom or two-bedroom unit. The threshold was chosen because 750 sq ft is roughly where an ADU transitions from a studio or small one-bedroom to a more livable, rentable dwelling.

What Newsom signed and what it means

AB 956 passed the California Senate on August 25, 2026 and was signed by Governor Newsom on September 29, 2026. SB 1117 passed the Assembly on August 20, 2026 (Senate concurring August 25), was enrolled and presented to the governor on August 30, and was also signed September 29, 2026. Both take effect January 1, 2027. Newsom has been consistently supportive of ADU-expansion measures — he signed four ADU bills in October 2025 and the September 29 package extends that record.

Why this matters in Solano County and the Bay Area

Solano County has something most of the Bay Area doesn't: room. Lots in Vacaville, Fairfield, and parts of Vallejo are large enough that two detached ADUs are genuinely buildable — not just theoretical. For a homeowner facing carrying costs in a market where prices have softened, two rental units instead of one changes the income math significantly. The same logic applies in Benicia, Martinez, Concord, and Antioch, where single-family lots tend to run larger than in Oakland or San Jose. For investors acquiring single-family properties as buy-and-hold rentals, a second detached ADU dramatically improves the return equation without requiring a commercial purchase.

Two ADUs on one lot — law as of January 1, 2027.

What the new law still doesn't change

Both bills are now law but take effect January 1, 2027 — so permits filed before that date still follow current rules. Beyond the effective date, local jurisdictions still apply setbacks, lot coverage limits, and height restrictions — AB 956 changes how many detached ADUs you can build, not those physical constraints. If your lot can physically accommodate two detached ADUs, you'll still need to confirm the numbers with Solano County or your city's planning department. And SB 1117 reduces fees but doesn't eliminate them; permit costs, utility hookup fees, and construction costs remain.

My read for clients: both bills are now signed and take effect January 1, 2027. The income and housing potential of a single-family property in Solano County is shifting — especially on larger lots in Vacaville, Fairfield, and north Vallejo where two detached units are physically realistic. If you own a single-family property or are evaluating one with ADU potential, the time to run the numbers is before January 1 — not after. I know which neighborhoods have the lot sizes to take advantage of the new rules and I'll give you a straight read on what they mean for your specific parcel.