AB 956: California Says Yes to Two Backyard ADUs

Starting January 1, 2027, a California city has to approve two new backyard homes behind a single-family house, not one. That is AB 956, signed by Governor Newsom on September 29, 2026, over the objections of the state's fire chiefs and city councils from Burbank to Cupertino. A second law signed the same day can cut the impact fee on an 800-square-foot cottage by about 94 percent from 2027.

The state's guarantee still tops out at four homes on the lot. A second cottage changes how a mortgage lender sees the house. And the fee cut signed the same day stops short of the full build-out. Here is what the law says, line by line, and what it means for your lot.

What exactly does AB 956 change on January 1?

Under AB 956, a California city must approve up to two detached, new-construction ADUs on a lot with an existing or planned single-family home in a residential or mixed-use zone, starting January 1, 2027. Until then the state guarantee is one.

The change sits in Government Code section 66323, which in the chaptered text of AB 956 now reads "Two detached, new construction, accessory dwelling units that do not exceed four-foot side and rear yard setbacks for a lot with a proposed or existing single-family dwelling."

The approval is ministerial, and that is the word that matters. A planner checks your plans against written rules and issues the permit if they comply. No public hearing, no discretionary "no."

Since 2025, a city also cannot add design rules of its own to these units, such as a required roof style. The state housing department, HCD, has written up cities for it, Calabasas among them in 2026. Building, fire and energy codes still apply, as they do to every house.

The bill also reaches into homeowners associations. From 2027, an HOA rule that "effectively prohibits or unreasonably restricts" an ADU is void on any lot zoned to allow a single-family home, not only one zoned for it, under Civil Code sections 4751 and 714.3. An association can still set reasonable rules. The statute's test is whether a rule unreasonably raises the cost, effectively blocks the unit or takes away the ability to build it.

The bill passed the Assembly 60 to 2 on August 27, 2026. Its author, Assemblymember Sharon Quirk-Silva of Fullerton, pitched it as a way for families to house aging parents and grown children, and California YIMBY sponsored it.

The opposition list in the Senate floor analysis ran from the League of California Cities and the California Fire Chiefs Association to Burbank, Carlsbad, Cupertino, Thousand Oaks and Torrance. Their argument was infrastructure: water, sewer, power and roads planned for the density cities have today.

The bill that came out of that fight carries one trade-off that is easy to miss.

So can you put five homes on one lot?

Not under the state guarantee. AB 956 lets you build two detached units, but it also says a city "is not required to ministerially approve" a junior ADU on a lot where two detached, new-construction ADUs have been built. The guaranteed maximum for a single-family lot stays at the main house plus three more homes, and from 2027 you choose which three.

The statute lets you combine options. One unit can come from converting existing space, such as a garage, a basement or part of the house. A junior ADU, up to 500 square feet, can sit inside the house. And up to two new units can go in the yard. Before 2027 the guarantee was conversion plus junior plus one new unit. From 2027 it can be conversion plus two new units instead.

The Senate's analysis of the bill explains the trade. A fifth home on a single-family lot would start to run into the state's density bonus rules, so the junior unit came out to keep the count at four.

For many families that is an easy trade. A JADU is a unit of up to 500 square feet carved out of the house itself, and it shares more of your life than a cottage across the yard.

AB 956 does not hand you a lot split, either. Splitting a lot into two parcels is a separate law, SB 9, with its own rules and a three-year owner-occupancy statement for the applicant. And in most cases the ADUs stay part of your property. Selling one separately as a condo depends on AB 1033, and only works in cities that have opted in.

Two details keep the number from being absolute. The law excuses the junior unit only once two detached units "have been constructed," so the order of permits on a lot is a question to put to your planning department. And some cities already allow more than the state minimum under their own ordinances. The state rule is a floor every city has to meet, not a ceiling on what yours may offer.

[[CTA-1 mid-article]]

Will two backyard homes fit on your lot?

Two units fit when the yard can hold two footprints of up to 800 square feet each, four feet off the side and rear lines, with a safe path for firefighters and room for utilities. On a one-story plan, two 800-square-foot cottages need about 1,600 square feet of ground before you count walkways and the space between them. A two-story plan needs a city that allows the height.

On a deep 50-by-150-foot lot, one layout looks like this: one cottage along a side line, one across the back, and an open strip between them.

Height decides whether a cottage can go up instead of out. Under Government Code section 66321, a city must allow at least 16 feet for a detached ADU. Within a half mile walk of a major transit stop or a high-quality transit corridor, the floor is 18 feet, plus two more feet if the roof pitch matches the main house. Two full stories are hard to fit under 16 feet.

So a two-story cottage comes down to height. HCD's ADU handbook says a city must allow a second story when it fits within the height limit that applies, and a city may set that limit higher than the state floor. Whether you can stack depends on how many feet your lot is allowed.

Four things can decide fit before square footage does:

• Fire-rated walls. Under the California Residential Code, a wall close to a property line can require fire-rated construction and fewer openings, depending on the distance and whether the unit has sprinklers. At four feet, it is a design question from day one.
• Fire access. Fire departments set access rules, including how far a hose has to reach from the street to the farthest wall. A second cottage at the back of a deep lot is the one that tests it. The law says sprinklers cannot be required in an ADU if the main house does not need them, but access is a separate rule.
• Utilities. State ADU law, carried forward in SB 1117, lets a city or water district require a detached new unit to have its own water or sewer connection, with a charge proportionate to its size or plumbing fixtures. Two units can mean two trench runs.
• Easements and slope. A utility easement across the back of the lot or a steep grade can take the space before any rule does.

All four can be checked on a site visit before anyone draws a plan.

This is also where prefab earns a look. Many factory-built models are sized near 800 square feet and one story, which matches the state's guaranteed path almost exactly. The Renology prefab ADU guide compares the California makers that publish an all-in price.

What do two units cost, and what do they rent for?

Renology's 2026 range for building one ADU in California is $200,000 to $415,000 ($215,000 to $385,000 in Los Angeles). Two detached units cost close to two full projects, less what they share. On the other side of the ledger, HUD's fiscal 2026 fair market rents for a one-bedroom in the Los Angeles area run $1,630 to $3,490 a month, depending on ZIP code.

The ranges come from the Renology cost index, updated September 2026, which aggregates The Renology's California city guides across sizes, sites and finishes.

Permit filings run lower: across 3,702 ADU permits filed with the City of Los Angeles from January 2021 to May 2023, according to the city's building permit records, the median declared value was $110,000. A declared value is the figure an owner writes down to calculate permit fees, and it rarely includes design, utilities and the builder's margin. The Renology ADU cost calculator walks through both.

Building two at once can save on the parts that are shared: design, mobilization, a trench run if the layout allows, and some plan review. It does not halve the bill. Two separate cottages each need a foundation, a roof, a kitchen and a bathroom, and fire-rated walls near the lot line can add cost. That is why the second unit is priced closer to a full project than to an add-on.

On rent, HUD's fair market rent is a benchmark, not a forecast for your cottage. HUD sets it near the 40th percentile of local rents, utilities included, and housing agencies use it to set what vouchers pay. Across the 474 Los Angeles-area ZIP codes in fiscal 2026, the most common one-bedroom figure, used in 178 of them, is $2,330 a month.

Those are gross numbers, before vacancy, insurance, maintenance and the property tax on the new construction. And not every ADU is rented. The Senate's analysis of AB 956, citing a 2021 UC Berkeley Terner Center survey, put the share of new ADUs rented out at about 51 percent, with about 18 percent housing a relative or friend rent-free.

How much does SB 1117 cut the fees?

SB 1117 (Chapter 809), signed the same day, changes how cities charge impact fees on an ADU larger than 750 square feet. For up to two ADUs on a lot, the fee is now charged "only on the area in excess of 750 square feet of interior livable space" starting January 1, 2027. Units of 750 square feet or less still pay no impact fee at all.

The effect is easiest to see with numbers. The fee on an ADU is a share of what your city charges for a new house the size of yours. Take a 2,000-square-foot house in a city whose impact fee for that house would be $20,000. These figures are an example, not a real city's schedule.

The 750-square-foot line used to be a cliff, where fifty extra feet could add thousands. SB 1117 turns it into a slope, so the size of each cottage can follow the floor plan instead of the fee schedule.

Now the catch. The new formula applies only "for up to two accessory dwelling units on a lot." A main house with a converted garage and two new cottages has three ADUs, and the statute sends a lot with more than two back to the old whole-unit formula. The statute does not say whether a junior ADU counts toward that two.

Three other charges sit outside the change. Water and sewer connection charges are not impact fees under the statute. School districts may levy their own fees on an ADU of 500 square feet or more. And permit and plan check fees are their own line.

Why would your lender care how many ADUs you have?

Because the mortgage rules count them. Fannie Mae's Selling Guide, as published in October 2026, says: "Only one ADU is permitted on the parcel of the primary one-unit dwelling." Freddie Mac's guide allows one ADU on an eligible one- to three-unit property. A second ADU can move a house out of the one-home-plus-one-ADU category those programs are built around.

What happens next depends on the lender and the house. Some will look at the property as a two- to four-unit home, which carries its own down payment, appraisal and income rules. FHA guidance already counts each ADU after the first as an additional unit. Others may point you to a portfolio loan, one the lender keeps on its own books under its own terms.

That matters on the day you refinance and on the day you sell, because the loans a future buyer can use shape what the house is worth to them. None of this makes a second cottage a bad idea. Fannie Mae now lets lenders count rent from one ADU toward a borrower's income, under conditions.

One conversation settles most of it. Before you design for two, ask a mortgage lender how they would underwrite your property with two ADUs on it, both for your refinance and for a future buyer's loan. This section describes published lending rules. It is not lending advice.

Should you wait for January or start now?

Design now and file once the law is in force: January 1, 2027 is a Friday, so for most permit counters the first weekday is January 4.

Until then a city has no state duty to approve a second detached unit, so a two-unit plan filed in December depends on what local rules allow. After that, Government Code section 66317 gives the city 15 business days to say whether an application is complete and 60 days to approve or deny a complete one, or it is deemed approved.

Sixty days sounds quick, and the clock is real. It runs, though, from a complete application, and corrections can restart the count. In The Renology permit timeline dataset, Los Angeles garage conversions, to an ADU or to a room, filed from 2021 to 2024 took a median of 144 days from first filing to issued permit, corrections included. Those are among the simplest permits of this kind, and half took longer.

The two numbers measure different things, and part of the gap is the back-and-forth of corrections. A complete, well-drawn set of plans is the best way to shrink it. The permit timeline dataset breaks the waits down by review track: in Los Angeles, garage conversions that qualified for counter plan check moved at a median of 106 to 112 days, while regular plan check took 243.

The first months of 2027 carry one more variable. The first months of 2027 carry one more variable: local paperwork written for the one-unit rule. Where a local ADU ordinance fails to meet state law, Government Code section 66316 makes it void and the city must apply the state standards, but a counter working from last year's checklist can still slow a file.

For many families the smart move is to design the lot for two even if they build one. Place the first cottage so the second still fits. Size the water and sewer lines for both. Leave the fire path open. A second unit you planned for costs far less than one you have to squeeze in around the first.

The Renology Take

Two backyard homes sounds like double the rent. On many lots it is something smaller and more useful: a reason to plan the first unit better.

A yard with honest room for two 800-square-foot cottages with a clean fire path and room for utilities is rarer than the headlines suggest. Add lending rules built around one ADU and a fee cut that stops at two, and the second cottage is where the math gets thin.

The bigger gift may be the fee cut, not the second unit. On a lot with one or two ADUs, a single 900-square-foot cottage now pays impact fees on 150 square feet.

How we checked this

We read the chaptered text of AB 956 (Chapter 791, Statutes of 2026) and SB 1117 (Chapter 809, Statutes of 2026) on the California Legislature's site on October 31, 2026, along with Government Code sections 66315, 66316, 66317 and 66321 as they currently read. Vote counts, the opposition list and the survey figures on ADU use come from the bill history and analyses published by CalMatters Digital Democracy.

Rents are HUD's fiscal 2026 Small Area Fair Market Rents for the Los Angeles-Long Beach-Glendale metro area, read from HUD's documentation system on October 31, 2026, across 474 ZIP codes. Permit waits come from the Renology permit timeline dataset, version 2026.1, which covers garage-to-ADU and garage-to-room conversion permits from city records. Lending rules come from Fannie Mae's Selling Guide section B2-3-04, Freddie Mac's ADU appraisal guidance and HCD's ADU handbook (March 2026).

The illustration at the top of this page was generated by Renology and shows no real property. The photograph, the lot diagram and the fee chart are not generated.

This page explains what the law says. It is not legal or lending advice. For a specific lot, check with your city's planning department, and for financing, with a licensed lender.