Two new California laws change the ADU math on January 1, 2027 — one lets a single-family lot hold two detached ADUs by right, and the other cuts the impact fees on larger ADUs by charging them only on the space above 750 square feet. Both were signed by the Governor on September 29, 2026. Neither is in force yet: the rules on this page’s sister guide to current law apply through December 31, 2026. Here is what changes, in plain English, and what it means if you are planning a project now.
What Changes on January 1, 2027
- AB 956 (Quirk-Silva), Chapter 791, Statutes of 2026 — a city or county must ministerially approve two detached, new-construction ADUs on a lot with an existing or proposed single-family home, up from one today (Government Code Section 66323).
- SB 1117 (Cervantes), Chapter 809, Statutes of 2026 — for up to two ADUs on a lot, impact fees on an ADU larger than 750 square feet are charged only on the area above 750 square feet, instead of on the whole unit (Government Code Section 66311.5).
- Everything else in state ADU law — ministerial approval, the 60-day decision clock, the ban on owner-occupancy requirements for ADUs — carries over unchanged.
AB 956 Explained: Two Detached ADUs, By Right
Author: Assemblymember Sharon Quirk-Silva. AB 956 changes a single word in Government Code Section 66323(a)(2) — “one” detached ADU becomes “two” — and that one word doubles the backyard potential of a single-family lot.
Who qualifies. Any lot with an existing or proposed single-family dwelling, in a residential or mixed-use zone. If your lot qualifies for one detached ADU today, it qualifies for two starting January 1, 2027. Approval is ministerial: no public hearing, no discretionary vote, no neighbor veto — the city checks the plans against objective standards and issues the permit.
The limits a city can still impose. Each detached unit must sit at least four feet from the side and rear lot lines. A city may cap each unit at 800 square feet of livable space, and may apply the state height limits in Section 66321. A city may not pile on extra objective standards the statute does not authorize, and — as before — the ADUs must be rented for terms longer than 30 days, not run as short-term rentals.
The JADU trade-off — read this before you design. Section 66323(b) is new: if two detached, new-construction ADUs are built on a lot, the city is not required to also approve a junior ADU on that lot. So the state-guaranteed maximum stays the main house plus three units — what changes is the mix. From 2027 you can choose:
- Two detached ADUs (each up to 800 square feet if your city uses the cap) — two full backyard homes, and no guaranteed JADU on top; or
- The existing combination — one ADU or JADU created within the home or an existing accessory structure, plus one detached ADU.
Which mix pays better depends on your lot and your goals. Two detached units at our published build ranges (a detached ADU runs roughly $250K–$450K depending on size and finishes) is a bigger project than a JADU conversion ($60K–$175K) plus one detached unit — but it also produces two fully independent, full-kitchen rental homes instead of one.
One more change in the same bill: AB 956 also widened the state ban on deed restrictions and HOA covenants that block ADUs. Covenants that effectively prohibit or unreasonably restrict an ADU are now void on any lot zoned to allow single-family residential use — not just lots zoned exclusively for single-family homes (Civil Code Sections 714.3 and 4751).
SB 1117 Explained: The 750-Square-Foot Fee Break
Author: Senator Sabrina Cervantes. SB 1117 amends Government Code Section 66311.5, the impact-fee statute. Impact fees are the one-time charges cities levy for infrastructure — parks, roads, and similar. (They are not utility connection or capacity charges; the statute treats those separately, and SB 1117 does not change them.)
What stays the same. An ADU of 750 square feet of interior livable space or less owes no impact fees at all, and a JADU of 500 square feet or less is likewise exempt. That has been the law for years and does not change.
What changes. Today, the moment an ADU crosses 750 square feet, the proportional fee is calculated on the entire unit — the “fee cliff.” From January 1, 2027, for up to two ADUs on a lot, the fee is still proportional to the size of the main house, but it is charged only on the area above 750 square feet. The law applies statewide, including in charter cities.
A worked example (square feet, not dollars — every city sets its own fee schedule, so the dollar savings vary by city):
- A 1,000-square-foot detached ADU: through 2026, the fee math runs on all 1,000 square feet. From 2027, it runs on 250 square feet — the chargeable area drops by 75%.
- An 850-square-foot ADU: fee math on 850 square feet today; on 100 square feet from 2027.
- A 1,200-square-foot ADU: on 1,200 today; on 450 square feet from 2027.
The catch — three or more ADUs. The subtraction only applies to lots with up to two ADUs. Put a third ADU on the lot — say, a garage conversion plus the two new detached units AB 956 allows — and Section 66311.5(c)(1)(C) keeps the old whole-unit proportional calculation. If you are planning a three-unit lot, run the fee math both ways before you commit to a configuration.
One honest unknown: the bill does not say whether the new fee rule keys off your application date or the date the city assesses the fees. If you are pulling a permit for a unit over 750 square feet in late 2026, ask your city — in writing — which rule it will apply.
What This Means If You’re Planning Now
- You can design for 2027 today. Plans, engineering, and site design for a two-detached-ADU project can be drawn now so the application is ready to file under the new rules. Nothing about the design process has to wait for January.
- Budget with today’s real ranges. Our published Southern California build ranges: JADU $60K–$175K, garage conversion $100K–$200K, attached ADU $180K–$300K, detached ADU $250K–$450K. The 2027 laws change what is allowed and what fees are charged — they do not change what construction costs.
- Expect cities to update their ordinances. Cities must conform their ADU ordinances to the new statutes, and HCD reviews them. Your city’s local standards (within the limits above) still matter — verify the details for your parcel before you submit.
- Do not let anyone sell you the old rules. If a designer tells you a single-family lot can only ever hold one detached ADU, or quotes impact fees on the full size of a 1,000-square-foot unit for a 2027 project, they are working from stale law.
Frequently Asked Questions
Can I build two detached ADUs on my lot in 2027?
Yes — from January 1, 2027, under AB 956, a city must ministerially approve two detached, new-construction ADUs on a lot with an existing or proposed single-family home. Each unit keeps four-foot side and rear setbacks, and your city may cap each at 800 square feet of livable space.
If I build two detached ADUs, can I still add a JADU?
The city is not required to approve one. AB 956’s Section 66323(b) says that where two detached ADUs have been built, a JADU is no longer part of the state-guaranteed package — the lot maximum stays the main house plus three units, and you choose the mix.
How much will SB 1117 save me on impact fees?
It depends on your city, because each city sets its own fee schedule — but the chargeable area is what shrinks. On a 1,000-square-foot ADU (on a lot with no more than two ADUs), the fee is calculated on 250 square feet instead of 1,000 from January 1, 2027. Units of 750 square feet or less remain fully exempt, as they are today.
Can I apply under the 2027 rules before January 1, 2027?
No — both statutes take effect January 1, 2027, and applications filed in 2026 are processed under the current law. You can complete your design work in 2026 so you are ready to file when the new rules open.
These laws are why a second backyard home that no city had to allow in 2025 becomes a by-right project in 2027. If you want to know what your parcel can carry under the new rules, call or text 888-627-1131 for a free consultation. ADU Cities is built by Mars Construction Industries Corp — CSLB #1138550 (A General Engineering, B General Building, C-36 Plumbing, C-20 HVAC). For the full history of the laws behind today’s rules, see our California ADU laws hub, and browse the ADU FAQ.
Sources: AB 956 (Quirk-Silva), Chapter 791, Statutes of 2026 — chaptered text, California Legislative Information; SB 1117 (Cervantes), Chapter 809, Statutes of 2026 — chaptered text, California Legislative Information. This page is general information, not legal advice.
