California’s 2027 ADU Law Changes: Two Detached ADUs and Lower Impact Fees
By the PermitSet drafting team · Updated · 6 min read
Quick answer
Starting January 1, 2027, California’s AB 956 lets owners of a single-family lot build two detached ADUs by right instead of one, and makes HOA rules that effectively prohibit or unreasonably restrict ADUs unenforceable. SB 1117 lowers ADU impact fees by excluding the first 750 square feet of each unit from the fee calculation. Both bills were signed on September 29, 2026.
AB 956: two detached ADUs by right
Under prior law, cities had to ministerially approve one detached new-construction ADU on a single-family lot. AB 956 doubles that to two detached ADUs.
Cities can still apply side and rear setbacks of up to four feet, an 800-square-foot size limit for these by-right units, and the statutory height limits to each detached ADU.
- Option A: one converted ADU + one junior ADU (JADU) + one detached ADU.
- Option B: one converted ADU + two detached ADUs (a JADU need not also be approved on that lot).
HOAs can no longer block ADUs
AB 956 makes covenants, conditions, and restrictions (CC&Rs) that effectively prohibit or unreasonably restrict ADUs or JADUs unenforceable, and extends that protection to any zone that allows a single-family home as a primary use.
SB 1117: lower impact fees
For lots with up to two ADUs, impact fees are now calculated by excluding the first 750 square feet of each unit. ADUs of 750 square feet or less, and JADUs of 500 square feet or less, remain exempt from impact fees. Utility connection and capacity charges are not covered by this change.
What homeowners should do now
- Check your lot: confirm zoning, lot size, setbacks, and where two detached units could physically fit.
- Plan both units together, even if you build in phases — utilities, access, and fire separation are cheaper to design once.
- Watch your city’s ordinance: local ADU rules must comply by January 1, 2027 or they become void.
- Get drawings started early: permit drawings typically take 1–2 weeks, and plan review queues tend to grow when new rules take effect.
Frequently asked questions
When does California’s two-detached-ADU rule take effect?
AB 956 takes effect January 1, 2027. It was signed by Governor Newsom on September 29, 2026.
Can my HOA stop me from building an ADU in California?
Under AB 956, HOA rules that effectively prohibit or unreasonably restrict ADUs or JADUs are unenforceable. HOAs may still apply reasonable rules that don’t effectively prohibit an ADU.
How big can a by-right detached ADU be in California?
Cities may apply an 800-square-foot size limit, up to four-foot side and rear setbacks, and statutory height limits to by-right detached ADUs. Many cities allow larger ADUs under their local ordinance.
Planning one ADU — or two?
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- PublicCEO — California further expands state accessory dwelling unit law (Oct 2026)
- California Department of Housing and Community Development — ADU resources
This guide is general information, not legal advice. Building codes and local ordinances change — always confirm requirements with your local building department.