California’s new ADU laws for 2027, in plain English.
Two bills signed September 29, 2026 change the backyard ADU math starting January 1, 2027: two new detached ADUs on a qualifying single-family lot, wider protection against HOA rules that block them, and impact fees figured only on the area above 750 square feet when the lot has no more than two ADUs. Here is what each bill says, what it does not say, and how it plays out in the energy report for each new building.
Two bills, one effective date
On September 29, 2026 the governor signed AB 956 (Quirk-Silva, Chapter 791) and SB 1117 (Cervantes, Chapter 809) as part of the year’s housing package. Neither has an urgency clause, so both take effect on January 1, 2027. Until then the current rules apply: on a lot with a single-family home, a city must approve one ADU converted from existing space, one junior ADU and one detached new-construction ADU, and impact fees on an ADU over 750 square feet are figured on the whole unit. Cities can allow more on their own, but they are not required to until the new year.
I am not a lawyer, and this is not legal advice. It is my reading of the final bill text, linked below, from the person who does the energy report. Confirm anything you build a budget or a site plan around with your city.
| Bill | Rule today | Rule from January 1, 2027 |
|---|---|---|
| AB 956 | A city must ministerially approve one detached, new-construction ADU on a lot with a single-family home, alongside a conversion ADU and a junior ADU. | A city must ministerially approve two detached, new-construction ADUs on that lot. It may still cap each at 800 square feet of livable space, apply the state height limits, and require side and rear setbacks of up to four feet. |
| AB 956 | HOA rules and deed restrictions that effectively prohibit or unreasonably restrict an ADU are void on lots zoned for single-family residential use. | The same protection reaches lots zoned to allow single-family residential use, which can include a house on land whose zoning also allows multifamily. |
| SB 1117 | No impact fees on an ADU of 750 square feet or less, or a junior ADU of 500 or less. Over 750, fees are charged in proportion to the primary home, on the ADU’s full area. | On a lot with no more than two ADUs, the proportional fee on an ADU over 750 is charged only on the area above 750 square feet. A lot with more than two ADUs keeps the full-area calculation. |
AB 956: two backyard cottages, with one catch
On a lot in a residential or mixed-use zone with an existing or proposed single-family home, a city has to approve two detached, newly built ADUs through the same by-right, no-hearing process it uses for one today. The guardrails did not move: the city may hold each unit to 800 square feet of livable space and to the height limits already in state ADU law, and it cannot require side or rear setbacks of more than four feet.
The section still says a city must approve any combination of the units it lists, with one exception (the junior ADU, below). Read that way, a qualifying ADU converted from space inside the house or an existing accessory structure can sit alongside the two new cottages. That is three ADUs on one lot, and it matters for fees: SB 1117’s 750-square-foot deduction only applies on lots with no more than two ADUs.
The catch is the junior ADU. The new law says a city is not required to approve a junior ADU on a lot where two detached, new-construction ADUs have already been built under the new rule. A city can still allow one; it just no longer has to. The text speaks only to a junior ADU that comes after the two cottages are built. It does not say what happens when the junior ADU comes first or is filed at the same time, so if one is part of the plan, settle the whole lot with the city before anything is filed.
The HOA change widens a protection that already exists. The Civil Code already voids covenants and HOA rules that effectively prohibit or unreasonably restrict an ADU. AB 956 changes the zoning test in both sections from lots zoned for single-family use to lots zoned to allow it. Reasonable design rules can still apply, but they cannot effectively block the unit or unreasonably raise its cost, and they cannot take the form of fees or other financial requirements.
What AB 956 does not do: it does not split the lot or create a right to sell each cottage separately. Units approved under this section still have to be rented for terms longer than 30 days, and a city still cannot make you correct existing nonconforming zoning conditions as a condition of approval.
SB 1117: fees only on the square feet past 750
Impact fees are the development charges that pay for things like parks and traffic. State law already bars them on an ADU of 750 square feet or less and a junior ADU of 500 or less. Over 750, they are charged in proportion to the main house, on the whole ADU, so an 800-square-foot unit is charged on all 800. Starting January 1, 2027, on a lot with no more than two ADUs, the same unit is charged on 50. The rule binds cities and counties, charter cities included, as well as special districts and water corporations.
In the Assembly Local Government Committee’s analysis, the bill’s opponents estimated that the fee on a 1,000-square-foot ADU would fall from $2,500 to $625. Real numbers depend on each agency’s fee schedule and the size of the main house.
Three charges this does not touch. Permit and plan check fees are processing fees, not impact fees. Water and sewer connection fees and capacity charges run under their own rules, which SB 1117 left as they were. School district fees follow the Education Code, with their own 500-square-foot line, so an ADU over 500 square feet can still owe them. The bill also has no transition rule for a project permitted before January 1 with fees not yet paid; if that is you, ask the agency in writing which calculation it will use.
What two cottages mean for Title 24
These bills do not change the Energy Code. What they change is how many new buildings end up on the lot. A new detached ADU is a newly constructed building under the Energy Code, so two cottages are two buildings, and each needs its own energy compliance. On a typical two-cottage lot I plan on two CF1Rs, one per building, each registered on its own.
Each building also gets its own solar answer. A new detached ADU generally needs newly installed PV; per the CEC, the new modules can be added to the main house’s system rather than going on the ADU roof, but an existing array on the house does not count by itself. The common exceptions are a required system under 1.8 kWdc and a solar access roof area (SARA) under 80 contiguous square feet. The 1.8 kWdc figure comes from an equation driven by floor area and climate zone: an 800-square-foot ADU works out to about 1.62 kWdc in climate zone 3, under the line, and about 1.85 kWdc in climate zone 9, over it. Roof shape and shading change the SARA, not that equation. The fuller rule is on does my ADU need solar.
If one of the units is a garage conversion rather than a new cottage, it follows the addition rules, which carry no PV requirement. On an apartment property the ADU counts follow different rules and the certificate depends on each building; a building of three or more units is low-rise multifamily, covered on Title 24 for multifamily ADUs. For everything else about the single-family report, see ADU Title 24 reports.
A permit application filed in January 2027 is still under the 2025 Energy Code, which covers applications filed on or after January 1, 2026, so the energy work for a two-cottage lot can be done now. Having it done takes one item off the January submittal list; the full plan set, signatures and any other approvals still have to be ready.
Sources: AB 956, Chapter 791, Statutes of 2026 (final text); SB 1117 final text as passed (signed as Chapter 809, Statutes of 2026); Assembly Local Government Committee analysis of SB 1117, July 1, 2026; HCD ADU Handbook, March 2026; 2025 Energy Code, Section 150.1(c)14 and Table 150.1-C; CEC 2025 ADU questions and answers; Governor’s signing release, September 29, 2026.
Prices
Flat fees, in writing before I start. No hourly, no bid package, no change-order games — the number on the quote is the number on the invoice.
One honest note
I’m not a licensed engineer or architect, and I don’t stamp drawings. On the CF1R I’m the documentation author — you stay the responsible designer. Nothing about your role on the job changes.
That’s on purpose. I’m not after your scope or your clients. I do one piece of the permit set — the piece that usually holds it up — and I do it fast.
New ADU law questions
If yours isn’t here, see the full FAQ or call and ask.
When do the new California ADU laws take effect?
January 1, 2027. AB 956 and SB 1117 were both signed on September 29, 2026, and neither has an urgency clause, so they take effect on the normal start date for this year’s bills. Until then a city only has to approve one detached new-construction ADU on a single-family lot, plus a conversion ADU and a junior ADU, though some cities already allow more.
Can I build two detached ADUs and a junior ADU on the same lot?
Not guaranteed. Starting in 2027 a city must approve two detached new-construction ADUs, but once those two have been built it is not required to approve a junior ADU on the same lot. A city may still allow one. The bill does not say what happens when the junior ADU comes first, so if one is in the plan, settle the whole lot with the city before filing.
Can my HOA still block an ADU?
Not if the ADU meets state ADU law. HOA rules that effectively prohibit or unreasonably restrict an ADU or junior ADU are already void, and from 2027 that covers any lot zoned to allow single-family use, not only lots zoned for it. Reasonable design rules can still apply, but they cannot include fees or other financial requirements.
How much does SB 1117 save on ADU impact fees?
It depends on the agency’s fee schedule. From January 1, 2027, on a lot with no more than two ADUs, the impact fee on an ADU over 750 square feet is figured only on the area above 750. Opponents quoted in the Assembly analysis estimated a 1,000-square-foot ADU would drop from $2,500 to $625. School fees and utility connection charges are separate.
Do two detached ADUs need two Title 24 reports?
On a typical lot, yes. Each new detached ADU is its own newly constructed building under the Energy Code, so I plan on a separate CF1R for each, registered on its own, with its own solar requirement or exemption. Both can be done from the same plan set at the same time, and the work falls under the 2025 Energy Code either way.
Drawing two cottages for January?
Send the set now. The energy work falls under the 2025 Energy Code either way, so both CF1Rs can be ready, each with its solar answer stated plainly, before the new law takes effect.