Two Detached ADUs Per Lot: What AB 956 Trades Away

The line that matters most in the enrolled text of AB 956 is the one nobody has quoted. It sits in subdivision (b), and it says a local agency is not required to ministerially approve a junior accessory dwelling unit on a lot where two detached, new construction ADUs have already been built. The headline everyone ran is true. California would go from one guaranteed detached backyard cottage on a single-family lot to two. The catch is that the second cottage can cost you the junior unit.

Governor Newsom has until September 30 to sign it or veto it. Until he does, this is a strong proposal, not something you can hand a contractor.

The whole change is one word

Strip away the digest language and AB 956 edits a single number. Government Code Section 66323 currently obliges every city and county in California to ministerially approve one detached, new construction accessory dwelling unit on a lot with a proposed or existing single-family home. The bill changes one to two. Everything attached to that unit stays put:

• Ministerial still means ministerial. No hearing, no design review, no neighbor testimony. A permit counter decision on a clock.
• Four-foot side and rear setbacks, unchanged. That is the provision that makes a rear-yard cottage physically possible on a narrow lot.
• A city may still cap the unit at 800 square feet of livable space and apply the state height rules in Section 66321, which start at 16 feet for a detached unit behind a single-family home.
• The standard ADU under Section 66314 and the conversion of existing space are untouched. Those run on their own tracks, and cities that allow more than the state floor keep allowing more.
• No state money follows the mandate. The bill's closing section says no reimbursement is required, on the theory that local agencies can charge fees to cover the work.

The sentence nobody has quoted

The trade shows up two paragraphs later. Under the enrolled version, a local agency is not required to ministerially approve a building permit for a junior ADU on a lot where two detached new construction ADUs have been constructed. Read that wording carefully, because the exact verb is doing a lot of work. The bill does not prohibit the junior unit. It removes the state's obligation to force cities to approve it.

That distinction is the difference between a hard ceiling and a local one. A city that wants the density can still say yes to all three. A city looking for a reason to say no now has one written into state law, and most planning departments will take it.

It also has a history. When the City of Murrieta wrote its opposition letter in April 2025, it described AB 956 as allowing two ADUs and a junior ADU, and objected that it amounted to writing four-unit density onto every single-family parcel. The enrolled version does not read that way anymore. Somewhere between that letter and the Senate floor, the junior unit became optional.

Run the arithmetic on an actual lot

Here is what the swap looks like on a Bay Area single-family parcel, counting only what state law guarantees. Today the ministerial package is a main house, one detached cottage of up to 800 square feet, and a junior ADU of up to 500 square feet carved out of the existing home. Under AB 956 it becomes a main house and two detached cottages, with the junior unit left to the city's discretion.

So the honest version of this bill is a quality upgrade on the third unit rather than a fourth home on every lot. Two freestanding 800 square foot cottages are a far better asset than one cottage plus a bedroom-and-kitchenette carved out of your own hallway. They rent for more, they appraise better, and they do not require you to give up part of the house you live in.

Whether the total goes higher than three depends entirely on where the lot is. Plenty of Bay Area cities already allow more than the state floor. In July, Redwood City raised its own cap to eight detached ADUs on multifamily lots, and cities that generous will almost certainly keep approving junior ADUs alongside two cottages. The carve-out matters most in the cities that were never enthusiastic in the first place.

A cottage and a junior unit are not the same asset

If you are choosing between them, the two products barely overlap. This is the comparison worth having before you sketch anything.

The owner-occupancy line is the one that changes behavior. We walked through that rule in our rundown of the 2026 ADU laws, and it is the reason junior ADUs got more useful this year, not less. But a junior unit still means a stranger sharing your wall. A second cottage 30 feet away is a different life.

In Silicon Valley, the cottage is the cheap part

The reason this bill lands harder here than in most of California is the land underneath it. A detached ADU costs roughly $250,000 to $500,000 to build in the Bay Area. Set that against what the dirt is already worth.

San Jose's median sale price was about $1.63 million in August 2026. Sunnyvale was about $2.46 million and Gilroy about $1.16 million in the same month. In Sunnyvale, a second 800 square foot cottage costs something like a fifth of the house it sits behind, and it can rent for real money. In Gilroy the same build is closer to a third of the property's value, and rents are lower, so the second unit has to work much harder to pencil.

That spread is the whole reason we treat this as a neighborhood question at Houseberry rather than a statewide one. The state can hand every homeowner the same permit right, and it will still mean something completely different across the 459 ranked Silicon Valley neighborhoods on our site, 358 of which are in San Jose alone. Before you spend half a million dollars in the backyard, the local rent and resale picture is the number that decides it.

The quieter change is in the Civil Code

The provision that will surprise people is not about counting units at all. AB 956 rewrites Civil Code Section 714.3, which voids deed restrictions and covenants that block ADUs, so that it covers any lot "zoned to allow single-family residential use" instead of any lot "zoned for" it. The bill makes a parallel edit to Section 4751 of the Davis-Stirling Act, which governs homeowners associations.

Two words, and the coverage widens a lot. A great many Bay Area single-family houses sit on parcels that are zoned R-2, R-3, or mixed-use, which allow single-family homes among other things. Under the old wording, an owner in that situation could plausibly be told the ADU protection did not apply and the 1962 tract covenant still did. Under the new wording, it applies. Every city that has upzoned a single-family neighborhood in the last three years has quietly created more parcels in exactly that category.

What is still unsettled

Three things are genuinely open, and anyone selling you certainty this week is guessing.

First, it is not law. The Governor has signed most of what the Legislature sent him on ADUs, but he has also vetoed housing bills he considered too prescriptive toward local agencies, and this one hands cities an unfunded mandate with no reimbursement.

Second, the 800 square foot condition is written in the singular. The enrolled text lets a city impose "a total floor area limitation of not more than 800 square feet of livable space" on the paragraph that now describes two units, without saying whether that means 800 each or 800 combined. The plain reading is per unit. A city that wants to limit backyard density will read the word "total" and try the other one, and somebody will end up litigating it.

Third, permits are not buildings. ADUs already do a lot of work in California, roughly 19 percent of all housing units produced statewide as of 2022 according to California YIMBY's analysis of state permit data. But a second cottage means a second sewer lateral, a second electrical service question, and a second round of utility fees. The permit right is free. The build is not.

Between now and September 30

If you own a Bay Area lot and a backyard unit is anywhere on your list, the useful move this month is to figure out which version of the math you want. A junior ADU inside the house and one cottage out back is still available and still legal under current law. Two cottages and no junior unit is the offer on the table if the Governor signs. They are not the same plan, and one of them is much harder to reverse once the walls come down.

Watch the bill's record for the signature. Then check your own city's ADU ordinance, because the state sets a floor and your city sets the ceiling. And if you are weighing whether the second unit is worth building at all, start with what the neighborhood around it is actually worth, which is the part we spend our time measuring.

Sources

• AB 956 enrolled text, California Legislative Information
• AB 956 bill record and status, CalMatters Digital Democracy
• California Government Code Section 66323
• City of Murrieta, letter of opposition to AB 956, April 2025
• California YIMBY, AB 956
• California YIMBY, California ADU Reform: A Retrospective
• Houseberry city price history, San Jose