Starting January 1, 2027, San Diego homeowners can build two detached ADUs on a single-family lot, and larger ADUs pay less in impact fees. Here's what AB 956 and SB 1117 actually change.
The 60-second version
San Diego ADU laws change on January 1, 2027. AB 956 lets San Diego homeowners build two detached ADUs behind a single-family home instead of one, each guaranteed up to 800 square feet.
SB 1117 removes the 750 sq ft fee cliff: for the first two ADUs on a lot, impact fees can only be charged on the square footage above 750.
The trade-off: if you build two detached ADUs, the city doesn't have to approve a junior ADU on the same lot. And utility, school, and permit fees aren't touched.
- Two detached ADUs per lot
- Effective January 1, 2027
- 800 sq ft guaranteed per unit
- No impact fees on the first 750 sq ft
- JADU not guaranteed with two detached
I'm Daniel Dechner, Lead Project Manager at IL Total Design & Build, a San Diego ADU design-build firm. California rewrites part of its ADU law almost every year, and most years the changes are procedural: deadlines, definitions, paperwork (like SB 543 in 2026). This year, two of them change what San Diego homeowners can actually build.
On September 29, 2026, Governor Newsom signed AB 956 and SB 1117. Neither law is as simple as the headlines make it sound. AB 956 comes with a trade-off most articles skip, and SB 1117 doesn't touch the fees that tend to surprise homeowners most. Here's what each law does, what's still unknown in San Diego, and how I'd plan a project around them if you're starting now.
San Diego ADU laws for 2027 at a glance
| AB 956 | SB 1117 | |
|---|---|---|
| What it does | Cities must approve two new detached ADUs on a lot with a single-family home | Impact fees on an ADU over 750 sq ft are charged only on the area above 750 sq ft |
| Effective | January 1, 2027 | January 1, 2027 |
| Applies to | Lots with an existing or proposed single-family home in a residential or mixed-use zone | The first two ADUs on a property |
| The catch | The city doesn't have to approve a junior ADU on the same lot | Utility connection, school district, and permit fees aren't affected |
Can you build two detached ADUs in San Diego? (AB 956)
Until now, state law guaranteed one new detached ADU on a lot with a single-family home. AB 956 raises that to two, in any residential or mixed-use zone, on a lot with an existing or proposed single-family home. "Proposed" matters: if you're building a new house, both ADUs can go in the same set of plans.
Approval is ministerial. City staff checks your plans against objective standards, with no public hearing and no neighbor appeal. Plan check and the building code still apply in full.
| Standard | State minimum under AB 956 |
|---|---|
| Size | Up to 800 sq ft of interior livable space per unit |
| Height | A city can't set a limit lower than 16 ft (18 ft near major transit, plus up to 2 ft to match the main roof pitch) |
| Setbacks | No more than 4 ft from the side and rear property lines |
| Rentals | Longer than 30 days; no short-term rentals |
These are floors, not ceilings. The City of San Diego already allows detached ADUs larger than 800 sq ft, and up to two stories in single-family zones. Whether the City will apply those larger local limits to both units under AB 956 is one of the open questions below.
A city can't require fire sprinklers in the ADUs if the main house doesn't need them. AB 956 also tightens the limits on HOAs: CC&Rs can't block or unreasonably restrict ADUs on lots zoned to allow single-family use.
The catch: you may give up the junior ADU
Under the state's guaranteed path, the realistic maximum is four homes: the main house, one ADU converted from existing space such as a garage, and two new detached ADUs. The City of San Diego's current version of four homes looks different: the main house, a JADU, a converted ADU, and one detached or attached ADU.
So for most lots, the real question isn't "can I build more?" It's "which layout fits my goals?"
| Layout | Usually the better fit when |
|---|---|
| One detached ADU + a JADU and/or garage conversion | You have a garage or underused space in the house and want to keep yard space |
| Two detached ADUs | You have yard depth and want two fully separate units with no shared walls with the main house |
For families housing aging parents or adult children, two detached units often means more privacy for everyone. For rental income, compare what each unit will rent for against what it costs to build. Converting space you already have usually costs less than building new, and that gap can decide the layout.
Will San Diego ADU fees go down in 2027? (SB 1117)
Under current state law, ADUs of 750 sq ft or less are exempt from most local impact fees. Go one square foot over and, in many jurisdictions, the fee is calculated on the whole unit. That's why so many ADU floor plans land at exactly 749 square feet.
SB 1117 changes the math for the first two ADUs on a property. If an ADU is over 750 sq ft, impact fees can only be charged on the square footage above 750, proportional to the main house. A 790 sq ft ADU is charged on 40 square feet, not 790. A third or later ADU on the same lot still pays on its full size.
| Reduced by SB 1117 | Not affected by SB 1117 |
|---|---|
| Local impact fees on an ADU over 750 sq ft (charged only on the area above 750) | Utility connection and capacity fees (in most of the City of San Diego, the Public Utilities Department) |
| ADUs of 750 sq ft or less stay fully exempt from impact fees | School district fees, which follow the district's own rules |
| Applies to the first two ADUs on a lot | Permit and plan check processing fees |
The practical result: going from 750 to 900 sq ft costs much less in impact fees than it did in 2026, and that matters on a family-sized one- or two-bedroom. On a two-ADU project, budget for two sets of utility connection fees. How much you save depends on what your jurisdiction charges, so get a fee estimate for your specific lot before you lock in a floor plan.
What the 2027 ADU laws mean in the City of San Diego
State ADU law applies directly to cities, so AB 956 governs on January 1 whether or not the San Diego Municipal Code has caught up. As of October 2026, the City's ADU rules allow one JADU, one converted ADU, and one detached or attached ADU on a single-family lot, and Information Bulletin 400 hasn't been updated for AB 956.
What we don't know yet, and I won't pretend to:
- Whether the City will let both detached units use its larger local size and height limits, or only the state's 800 sq ft and 16-foot minimums
- How AB 956 projects will be handled in High and Very High Fire Hazard Severity Zones, where the City already requires 4-foot fire safety setbacks for ADUs
- How the City will treat applications submitted in late 2026 that are still in review on January 1
We'll update this article as the City publishes its guidance.
AB 956 vs. the ADU Bonus Program
The City's ADU Home Density Bonus Program already allows more units than state law, in exchange for deed-restricted affordable units. Since the City's August 2025 reforms, it comes with real conditions:
- Not allowed in most RS-1 zones unless the site is in a High or Highest Resource area
- A cap of 4 ADUs on lots up to 8,000 sq ft, 5 on lots up to 10,000 sq ft, and 6 above that
- Fire sprinklers in all bonus and affordable ADUs
- One parking space per bonus or affordable ADU outside a Transit Priority Area
- A Community Enhancement Fee on bonus and affordable units under 750 sq ft
For homeowners who want a second detached unit without a deed restriction, AB 956 is now the simpler path. The Bonus Program still makes sense for owners who want five or six units and can carry the affordability covenant and the added costs. We run both scenarios on a lot before a client commits to either. If your lot is already near its limit, see what to do with a maxed-out lot.
For the full city-by-city breakdown, see our San Diego ADU regulations guide.
Do the new ADU laws apply in North County and unincorporated San Diego County?
Yes. AB 956 and SB 1117 are statewide, so they apply in Encinitas, Carlsbad, Oceanside, and unincorporated San Diego County too. Each jurisdiction will apply them through its own ordinance, fee schedule, and plan check process, so expect implementation to vary.
Coastal lots need extra care. AB 956 applies in the coastal zone, but a city's certified Local Coastal Program can still add limits, and coastal permitting adds its own review. The Coastal Commission and the state housing department published guidance on ADU permitting in the coastal zone on July 1, 2026 (we cover it in our North County coastal ADU guide). If your lot is in La Jolla, Pacific Beach, Ocean Beach, Encinitas, coastal Carlsbad, or coastal Oceanside, confirm the coastal requirements before assuming two detached units will move as fast as they would inland.
How to plan a San Diego ADU project starting now
- Building one ADU now?Place it so a second detached unit can fit later. Size the water, sewer, and electrical service for two units, and keep a clear path to the back of the lot. If two units push you into an SDG&E service upgrade, file early.
- Planning two units?Decide early whether a JADU or garage conversion matters more to you than a second detached unit. Under AB 956, you may not get all three.
- Sizing a unit?Treat 750 sq ft as a design choice, not a wall. Price a 749 sq ft plan and a larger plan side by side with SB 1117 in mind.
- Close to submitting?If a second detached unit is in the plan, ask how your jurisdiction will treat applications that straddle January 1 before you decide whether to submit now or wait.
- Check the site first.The law guarantees approval of units that meet the standards. It doesn't guarantee two buildings fit on your lot once you account for setbacks, access, utilities, slope, and trees.
Wondering if two ADUs fit on your lot?
We'll check your jurisdiction, coastal status, utilities, and fee thresholds, then tell you which layout makes sense and what each option costs in a free feasibility check.
Get a free feasibility check Call (619) 404-0125AB 956 and SB 1117 FAQ
When do AB 956 and SB 1117 take effect?
How many ADUs can I build in San Diego in 2027?
Can I build two detached ADUs in San Diego right now?
How big can each ADU be under AB 956?
Can I still add a junior ADU if I build two detached ADUs?
Does SB 1117 eliminate ADU fees?
Can I sell one of the ADUs separately?
Do I have to live on the property?
Do the new ADU laws apply in Encinitas, Carlsbad, and Oceanside?
Is AB 956 the same as an SB 9 lot split?
Not legal advice. This page summarizes California AB 956, SB 1117, and related ADU law as of October 2026 for general informational purposes. Cities will update their rules through 2027, and ADU requirements vary by jurisdiction and property. IL Total Design & Build provides design, permitting coordination, and construction services; it is not a law firm. Confirm current requirements for your property before you design.
