Guide
What changes for ADUs in San Diego on January 1, 2027?
The short answer
Two state laws signed on September 29, 2026 start that day in every city and in the unincorporated County. AB 956 raises the number of newly built detached ADUs a permit office must approve beside a single-family home from one to two, each of which may be held to 800 square feet, and it widens the rule against HOA and deed bans. SB 1117 lets an ADU over 750 square feet be charged impact fees only on its extra area, when the lot holds one or two ADUs.
Two detached ADUs on a single-family lot (AB 956)
AB 956 amends Government Code 66323, the short list of units every permit office has to approve ministerially, with no hearing, in a residential or mixed-use zone. Through the end of 2026 the list holds one detached, newly built ADU on a lot with a house, existing or proposed. From January 1, 2027 it holds two.
| Point | What the statute says from January 1, 2027 |
|---|---|
| How many | Two detached, new construction ADUs on a lot with a proposed or existing single-family dwelling. Through 2026 the number was one. |
| Size | The permit office may hold each of the two to 800 square feet of livable space. |
| Setbacks | No side or rear setback over 4 feet may be asked of either unit. |
| Height | Each may be held to the state's ADU heights in Government Code 66321, which AB 956 leaves as they were. |
| Other local standards | None beyond what the section itself allows, for any unit on its list; that rule moved from 66323(b) to 66323(c). |
| A junior ADU on the same lot | Once two detached units have been built under this rule, the office is no longer required to approve a junior ADU on that lot, though it may. A junior ADU still goes with one detached unit, as before. |
The junior ADU sentence turns on two units that "have been constructed". It does not say how an office should treat a junior ADU filed in the same application as two detached units, so that is a point to raise at intake until HCD writes it into a new handbook.
The bill also shifted the later letters of 66323 down by one without changing their words: the rental term of more than 30 days becomes 66323(f), the sprinkler rule (e), the nonconforming zoning rule (d) and the percolation test (g). A handout that cites 66323(e) for rentals will be one letter off from 2027.
Impact fees on ADUs over 750 square feet (SB 1117)
SB 1117 rewrites a single paragraph of Government Code 66311.5, the state's cap on impact fees that a city, the County, a special district or a water corporation may put on an ADU. The bill states that it reaches charter cities as well.
- At or under the line: an ADU of 750 square feet of interior livable space or less, and a junior ADU of 500 or less, pay no impact fee. That was already the law and stays.
- One or two ADUs on the lot: a unit over 750 square feet may be charged in proportion to the main house's size, and only on its area beyond 750.
- Three or more ADUs on the lot: the earlier rule holds, a charge in proportion to the house on the unit's whole area.
The method in words, with one example. Picture a 1,000 square foot ADU behind a 2,000 square foot house. Under the rule in force through 2026, its impact fee is the house's fee scaled by 1,000 over 2,000, so half. From 2027 the proportion is taken on the 250 square feet past 750 instead, which here works out to an eighth. The statute gives the method, not a formula, so each agency's fee sheet settles the arithmetic.
What the bill leaves alone matters as much. Water and sewer connection fees and capacity charges sit outside its definition of an impact fee, and permit, plan check and inspection charges are processing fees. School districts set their fees under the Education Code, which SB 1117 does not amend, so a lower school fee should not be assumed; the rule that an ADU under 500 square feet adds no assessable space stays.
HOAs and deed restrictions: "zoned for" becomes "zoned to allow"
Civil Code 714.3, which covers any deed, contract or other instrument, and Civil Code 4751, which covers a planned development and its HOA's governing documents, already void a covenant or rule that effectively prohibits or unreasonably restricts an ADU or junior ADU. AB 956 does not create that protection. It changes which lots it covers: from 2027 a lot zoned to allow single-family use, where the old words were a lot zoned for it.
The lots that gain are those in a zone that permits a house without being limited to houses, such as a mixed-use or multifamily zone where a home is one of the allowed uses. A covenant or association rule on such a lot that bans an ADU built to state law is void once the change takes effect.
Reasonable restrictions survive, meaning rules that do not unreasonably add to the cost or rule the unit out. Under 714.3 they still cannot take the form of a fee or any other financial requirement. In the county this reaches furthest in master-planned communities with their own associations and in Rancho Santa Fe, whose 1928 Protective Covenant is read against Civil Code 4751.
What does not change on January 1, 2027
- Sizes and heights. Neither bill amends Government Code 66321, so its 850 and 1,000 square foot figures, its 800 square foot floor and its height limits read as before; AB 956 only applies the 800 square foot cap and those heights to each of the two detached units.
- Conversions. A unit carved out of a house or an existing accessory structure, with up to 150 square feet added for its entrance, is on the list exactly as before.
- Junior ADU rules. Article 3 of the ADU law, from Government Code 66333 on, is untouched: the size, the entrance, the kitchen and the owner rules stay.
- Lots with apartments. The counts for conversions inside a multifamily building and for detached units beside one are unchanged.
- Rentals, sprinklers and septic. A lease must still run longer than 30 days, sprinklers still cannot be required when the house has none, and the percolation test rule stands; only their letters moved.
- Fees under the line, and the other charges. No impact fee at 750 square feet or less for an ADU or 500 for a junior ADU, with connection fees, capacity charges and school fees where they were.
- Parking and the coast. Neither bill touches the state's ADU parking rules or the Coastal Act, so a lot in the Coastal Zone still needs whatever coastal permit it needed before.
What it means across San Diego County's 19 permit authorities
The 18 cities and the County each keep an ADU ordinance, but under Government Code 66316 a local ADU ordinance that falls short of the state's ADU article is null and void, and the office applies the state's standards in its place. So from January 1, 2027, a code or handout that still names one detached unit, or scales the fee on a large ADU by its whole area, gives way to the statute.
Most codes in the county predate both bills. Lemon Grove's 2022 code and National City's 2021 sections still read one ADU and one junior ADU, and National City's Planning Commission started a rewrite in October 2026 meant to take AB 956 in. Chula Vista repealed its own ADU sections in 2025 and Imperial Beach's ordinance still waits on the Coastal Commission, so both work from the Government Code as written and pick up the new count with it.
A few places already went further than the old floor. Escondido's July 2026 article allows a Standard ADU of up to 1,200 square feet on top of the detached unit the state requires, and the City of San Diego's bonus program can allow four, five or six ADUs and junior ADUs on a single-family lot when some are kept affordable. On fees, the City of San Diego waives its own development impact fees on the first two ADUs at any size, so SB 1117 changes little there.
What to ask the permit office
HCD's ADU handbook was last updated in March 2026, before either bill passed, so until HCD revises it the bill text is the only state word on these points. These are the questions worth putting to the office that will issue your permit:
- Will you approve two new detached ADUs on this lot under the amended 66323, and will you hold each one to 800 square feet?
- Which of the state's height limits applies to each unit here?
- If two detached units and a junior ADU go in together, will you approve the junior ADU with them, given that the statute speaks of detached units already built?
- Which of your charges count as impact fees, and for a unit over 750 square feet, will you figure them on the area past 750?
- Does your ordinance or handout still name one detached unit, and if it does, will you apply the statute at intake?
- If the lot is in the Coastal Zone, which coastal permit does a second detached unit need, and who issues it?
- If the application goes in before January 1, 2027, can it be revised to add the second unit once the law is in force?
Questions homeowners ask about the 2027 changes
Each answer starts with the one-sentence version, then the detail.
Can I build two detached ADUs on my lot in 2027?
Yes, from January 1, 2027 a permit office in a residential or mixed-use zone must approve an application for two newly built detached ADUs beside a single-family home when each meets the state's standards. It may hold each to 800 square feet and the state's heights, and may ask no side or rear setback over 4 feet. Septic, fire access, utilities and a coastal permit can still shape what fits.
Can I still add a junior ADU if I build two detached ADUs?
Not by right: once two detached units are built under AB 956, the office does not have to approve a junior ADU on that lot, though it may choose to. Beside a single detached unit, a junior ADU is on the state's list as it was.
Will SB 1117 lower my water, sewer or school fees?
No, because it changes only impact fees under Government Code 66311.5, and connection fees, capacity charges and school fees sit outside that change. The fee it can lower is the impact fee on an ADU over 750 square feet, on a lot with one or two ADUs.
Can my HOA stop me from building an ADU?
It cannot ban one or restrict it unreasonably on a lot zoned to allow a single-family home, and from 2027 that wording covers more lots than "zoned for" did. An association may still apply reasonable rules, and under Civil Code 714.3 those rules cannot be a fee.
Does my city's older ADU ordinance still apply in 2027?
Only as far as it meets state law: Government Code 66316 makes a local ADU ordinance that falls short null and void, and the office then applies the state's standards. Where a code in the county still counts one detached unit, the statute's two govern from January 1, 2027.
Are ADU size or height limits changing in 2027?
No, neither bill amends the size and height rules of Government Code 66321. AB 956 only lets the office apply the 800 square foot cap and those heights to each of the two detached units.
Next steps
Find the office that reviews your lot, read its own page, then weigh one detached unit against two.