San Francisco Gets Two Detached ADUs on January 1, 2027
A new California law changes what a San Francisco single-family lot can hold — but not until January 1, 2027, and not on every lot. Here is what will change, what it will trade away, and how to be ready without over-promising your own rear yard.
The short answer
From January 1, 2027, a single-family lot will be able to have two detached new-construction ADUs by right — each up to 800 sq ft, with 4-foot side and rear setbacks.
That is a future right, not a current one. Until January 1, 2027, San Francisco Planning’s guidance still states the old rule of one detached ADU. Three honest qualifications come with the new right:
- The JADU trade-off: if you build the two detached ADUs, the city will not be required to also approve a junior ADU (JADU) on the same lot.
- The lot-fit reality: two detached units will fit mainly on deeper, wider, corner and Excelsior-type lots. On a typical 25-foot-wide mid-block Sunset or Richmond lot, they usually will not fit.
- Fee relief comes with it: under a companion law, SB 1117, impact fees on a larger ADU will be charged only on the floor area above 750 sq ft, from 2027.
Use 2026 to design, choose your programme carefully, and screen your lot — so a 2027 application starts from real plans, not from a headline.
Sources, as of November 2026: AB 956 (Chapter 791, Statutes of 2026) and SB 1117 (Chapter 809, Statutes of 2026), chaptered texts, amending Government Code §66323(a)(2); San Francisco Planning Code §207.2 (State Mandated ADU Program) and San Francisco Planning Director’s Bulletin No. 3. This page is dated as of November 2026 and will be re-verified on December 28, 2026, ahead of the January 1, 2027 effective date, and again when San Francisco Planning issues revised guidance.
Before and after
2026 vs. 2027 in San Francisco
Read every date on this page in the future tense until January 1, 2027. The table below is the whole change in one view.
| Question | Through Dec 31, 2026 | From Jan 1, 2027 |
|---|---|---|
| Detached new-construction ADUs on a single-family lot | One detached ADU — the rule San Francisco Planning’s Director’s Bulletin No. 3 still states as of November 2026. | Two detached new-construction ADUs by right, under Government Code §66323(a)(2) as amended by AB 956. |
| Size and setbacks for those units | Governed by the current rules and programme you build under. | Each detached ADU up to 800 sq ft, with 4-foot side and rear setbacks. |
| Can a JADU sit alongside them? | The two-detached option does not exist yet, so the trade-off does not arise yet. | If the two detached ADUs are built, the city will not be required to also approve a JADU on the lot. |
| Can an HOA restrict the ADUs? | Existing association restrictions apply as they stand today. | The bar will expand: associations will not be able to unreasonably restrict ADUs on lots zoned to allow single-family use (Civil Code §§4751/714.3 as amended). |
| Impact fees on an ADU over 750 sq ft | The SB 1117 relief described below will not yet be in effect. | Under SB 1117, impact fees will be charged only on the floor area above 750 sq ft — for up to two ADUs per lot. |
| Which San Francisco programme? | State-mandated ADUs run through San Francisco’s State Mandated Program, Planning Code §207.2. | The new detached units will be state-mandated ADUs, so the §207.2 route is the one to plan around. |
This is a summary of the verified law change for San Francisco single-family lots. It is not a feasibility finding for any individual parcel — that depends on your lot’s actual width, depth, rear yard and existing buildings, which is what the checker at the bottom of this page screens for.
AB 956, plainly
What AB 956 changes — three elements
AB 956 does one main thing, with two supporting changes. Keeping them separate keeps the promise honest.
1. Two detached units, by right
From January 1, 2027, a single-family lot may have two detached new-construction ADUs by right. “By right” and “detached new-construction” both matter: these are two separate backyard buildings, built new — not a conversion of an existing garage, storage level or part of the main house, and not a total of two units counting the main house. The main house plus two detached ADUs is the picture.
2. A standard size and setback for each unit
Each of the two detached ADUs may be up to 800 sq ft, placed with 4-foot side and rear setbacks. That standard size is what makes early design work possible in 2026: you can test a real footprint against your rear yard now, instead of guessing at a size the law has not set. It does not make the footprint fit — the lot-fit section below is blunt about that — but it gives you a fixed shape to test.
3. The HOA bar expands
The amended Civil Code provisions (§§4751/714.3) will expand the protection against association restrictions: an HOA will not be able to unreasonably restrict ADUs on lots zoned to allow single-family use. If your property sits in a condominium or planned-development structure with association rules that currently say no, this element is the one written for your situation — and it is still a future-tense change until January 1, 2027. Bring the actual CC&Rs to any serious screening; a general statement about HOAs is not a reading of your documents.
The trade-off, stated plainly
Two detached ADUs replace the JADU path — they do not stack on top of it
Here is the part the headlines skip. If two detached ADUs are built on a lot, the city is not required to also approve a JADU on that lot. So the real 2027 choice is not “two detached plus a junior unit.” It is closer to: two full detached backyard homes, or a different combination that keeps a JADU in the mix.
Which side of that trade is right depends on who the units are for. Two detached 800 sq ft units suit two separate households, or a household plus a rental. A JADU — a smaller unit inside the main house — can suit a family member who wants to be under the same roof rather than across the yard. Decide that on purpose, in 2026, before drawings lock the choice in. Once two detached units are the project, do not budget, promise family, or plan rents on a JADU the city is not required to approve.
SB 1117
The fee relief — and how it actually works
SB 1117 changes the basis impact fees are charged on, from 2027. For an ADU over 750 sq ft — up to two ADUs per lot — impact fees will be charged only on the floor area above 750 sq ft, instead of on the unit’s whole floor area.
The mechanics, in square feet only:
- An 800 sq ft ADU will pay impact fees on 50 sq ft — the area above 750 — not on 800 sq ft.
- A 760 sq ft ADU will pay impact fees on 10 sq ft.
- An ADU at or under 750 sq ft has no area above the threshold for this relief to apply to.
We are deliberately not turning that into a dollar saving on this page. A dollar figure would have to come from San Francisco’s own fee schedules for your specific project, and inventing a tidy example number would mislead you. What you can bank is the shape of the relief: the larger of the two effects is on full-size 800 sq ft units, where almost the entire floor area drops out of the impact-fee basis. When you screen your lot below, treat fees as a real project input to be priced from San Francisco schedules at application time — not as a number a guide page can promise in advance.
The San Francisco layer
State law changes; San Francisco guidance has not caught up yet
In San Francisco, state-mandated ADUs run through the city’s State Mandated Program under Planning Code §207.2. That is the programme these two detached units will run through, and it is the programme to design around in 2026.
One dated fact deserves its own paragraph: as of November 2026, San Francisco Planning’s Director’s Bulletin No. 3 still states the old one-detached-ADU rule. That does not cancel AB 956 — the state law takes effect January 1, 2027 regardless — but it means the city document a homeowner is most likely to find first still describes 2026, not 2027. San Francisco Planning is expected to revise its guidance, and this page will be updated when it does. If a contractor, neighbour or older guide quotes the one-detached rule at you, check the date on what they are quoting.
DEC 28, 2026
Our re-verification date
This page carries an “as of November 2026” date, and we have committed to re-verifying its law claims on December 28, 2026 — before the effective date — rather than letting a future-tense page drift quietly into the present tense.
JAN 1, 2027
The law takes effect
AB 956’s two-detached-ADU right and SB 1117’s impact-fee relief both operate from January 1, 2027. Everything on this page is written in the future tense until that date arrives.
Programme choice deserves a pause before you design too far. San Francisco homeowners generally weigh the State Mandated Program (§207.2) against the local programme (§207.1), and that choice carries consequences beyond the building itself — including for renting the finished unit. Those consequences have their own page, because they are easy to get wrong in a summary: read whether your San Francisco ADU will be rent controlled before you settle the programme, not after.
Lot-fit honesty
Will two detached units actually fit your lot?
For most San Francisco lots, this is the real question — and the honest answer splits sharply by lot type. Two detached units are a right on paper everywhere the law applies; they are a physical possibility mainly where the rear yard can take two buildings, their 4-foot setbacks, and real open space left over.
Where two detached is realistic
- Deeper lots with a long rear yard behind the main house — room for two footprints in sequence or side by side, without consuming the whole yard.
- Wider lots than the San Francisco standard, where two units can sit across the width with their side setbacks honoured.
- Corner lots, where the second street frontage changes the geometry of access, light and placement.
- Excelsior-type lots — the deeper, more generous parcels found in the Excelsior and similar outer neighbourhoods are the recurring real-world candidates.
Where it usually will not fit
- A typical 25-foot-wide mid-block Sunset or Richmond lot. Once 4-foot side and rear setbacks and remaining open space are honoured, two separate detached buildings usually do not fit. The arithmetic of the lot, not the law, is the blocker.
- Victorian and Edwardian rows on standard lots, where the house already runs deep on the parcel and the rear yard is modest — one well-placed detached unit, or a conversion, is often the honest project instead.
- Any lot where “fitting” means paving the entire rear yard. If the plan only works by eliminating the open space, it is not a plan a homeowner should be sold.
No page can promise that two detached units fit your lot, and this one does not. What screening can do in 2026 is sort your lot into the realistic group or the unlikely group early — before design money is spent drawing two buildings a 25-foot lot cannot hold.
Illustration only. A deep-lot arrangement in plan view — main house at the street, two detached units in the rear yard. It is a diagram of the idea, not plans for any property, and it deliberately shows the generous lot type where two detached units are realistic.
Be ready, not rushed
What to do in 2026
You cannot use a January 2027 right in November 2026. You can absolutely arrive at January 2027 with the thinking done. In order:
Screen the lot before you design anything
Width, depth, rear yard, corner or mid-block, existing buildings. If your lot is in the “usually will not fit” group above, finding out now redirects you to the one-unit or conversion project that actually works — while there is still time to pursue it properly. The checker at the bottom of this page is pre-set for exactly this question.
Decide the JADU trade-off on purpose
Two detached units, or a combination that keeps a JADU available? That is a household decision — who lives where, under one roof or across the yard — before it is a design decision. Make it once, early, and let the drawings follow it.
Choose the programme with its consequences in view
Plan around the State Mandated Program (§207.2) for these units, and understand what the §207.2-vs.-§207.1 choice means for renting the finished homes before you commit. Our San Francisco rent-control guide walks through that decision — it is the cluster page every San Francisco guide on this site points to, for a reason.
Design to the known standard
800 sq ft per unit and 4-foot side and rear setbacks are known now. Design work done against those fixed dimensions in 2026 is not wasted work — it is the head start. Keep the design honest about open space, and keep your HOA documents in the file if an association is involved, so the expanded HOA bar can be applied to your actual CC&Rs when it takes effect.
Homeowner questions
Two detached ADUs in 2027 — questions, answered
What exactly changes on January 1, 2027 — and what doesn’t?
From that date, a San Francisco single-family lot may have two detached new-construction ADUs by right, each up to 800 sq ft with 4-foot side and rear setbacks, under Government Code §66323(a)(2) as amended by AB 956. The HOA bar expands, and SB 1117’s impact-fee relief begins. What does not change: the law is not in effect before January 1, 2027, San Francisco Planning’s Bulletin No. 3 still stated the old one-detached rule as of November 2026, and no lot gains physical space it does not have.
Does the second detached unit replace my JADU?
In effect, you choose. If two detached ADUs are built on the lot, the city is not required to also approve a JADU there. So plan on two detached units or a combination that keeps a JADU — not all three as of right.
Will two detached units fit on my 25-foot Sunset or Richmond lot?
Usually not. On a typical 25-foot-wide mid-block lot in the Sunset or Richmond, two separate detached buildings generally do not fit once 4-foot side and rear setbacks and remaining open space are honoured. Two detached is realistic mainly on deeper, wider, corner and Excelsior-type lots. Screening your specific lot is the way to get a preliminary answer for your parcel rather than a neighbourhood generalisation.
How much will SB 1117 save me on fees?
The relief is mechanical, not a fixed dollar amount: from 2027, for an ADU over 750 sq ft (up to two per lot), impact fees are charged only on the floor area above 750 sq ft. An 800 sq ft unit pays on 50 sq ft, not 800. The dollar value depends on San Francisco’s fee schedules applied to your project, so this page gives you the square-foot mechanics and no invented dollar example.
My HOA says no ADUs. What changes for me?
From January 1, 2027, the Civil Code bar expands so associations cannot unreasonably restrict ADUs on lots zoned to allow single-family use (Civil Code §§4751/714.3 as amended). That is a future-tense change, and how it applies depends on your association’s actual documents — have your CC&Rs read against the amended law rather than relying on a summary.
Can I design and prepare in 2026, to be first in 2027?
Yes — that is the intended use of 2026. The size and setback standard (800 sq ft, 4-foot setbacks) is already known, the programme route (§207.2) is known, and lot screening can sort realistic lots from unlikely ones now. What 2026 work cannot do is make the right itself arrive early.
Keep reading
Related San Francisco guides
AB 1033 · Sell separately
Building an ADU You Can Sell Separately
San Francisco opted in to AB 1033. The strict eligibility test — application date, §207.2 programme, four units or fewer, one ADU, no JADUs — element by element.
Programme choice · Rent control
Will Your San Francisco ADU Be Rent Controlled?
The §207.2-vs.-§207.1 choice and its rent consequences — read it before you settle the programme for any San Francisco ADU, one unit or two.
District 4 · Sunset
ADUs in the Sunset District
What fits a 25-foot Sunset lot, honestly: garage and lower-level conversions first, and what San Francisco permit data actually shows for District 4.
Check your lot
Is your San Francisco lot a two-detached lot?
The checker below is pre-set to San Francisco, and pre-set to the “2 ADUs” want — because that is the question this page exists to answer. Give it your address and what you are hoping for, and it returns preliminary, plain-language guidance: which group your lot looks like it falls into, and what would need professional or city verification before anyone draws two buildings. It applies no Marin fees, rules or costs to a San Francisco property, and it makes no parcel-specific promise a screening cannot keep.
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