For Accessory Dwelling Units (ADUs) in San Francisco, the Planning Code does not impose any minimum size for an individual room within the ADU. The Code is clear that the City cannot require any minimum or maximum overall size for an ADU that would prevent the construction of an ADU up to 800 square feet in gross floor area, provided all other requirements are met. There is no clause specifying a minimum square footage for rooms within ADUs, only maximum square footages for total ADU size applicable in some circumstances. Likewise, Junior ADUs (JADUs) are limited to a maximum of 500 square feet but have no stated minimum room size.
What the Planning Code says
...the City shall not impose any requirement for a zoning clearance or separate zoning review, any minimum or maximum size for an ADU, any size based upon a percentage of the proposed or existing primary dwelling, or any limits on lot coverage, floor area ratio, open space, front setbacks, and minimum lot size, for either attached or detached dwellings, that does not permit construction of an ADU meeting all other requirements that is 800 square feet or less in Gross Floor Area, 16 feet or less in height, and with four foot side and rear yard setbacks....
And for Junior ADUs:
A Dwelling Unit that meets all the requirements of Section 207.2, and that: (a) is accessory to at least one other Dwelling Unit on the same lot; (b) is no more than 500 square feet of Gross Floor Area; (c) is contained entirely within an existing or proposed single-family structure;....
Because the Code prohibits imposing a minimum room or ADU size that would prevent construction of an ADU of up to 800 square feet, no separate room-size minimum applies under the Planning Code. This mirrors State ADU law. The building code is a different matter, and it is the one that sets a floor.
The building code is a different question
The Planning Code governs land use — how many units, how large, where on the lot. It is not the code that decides whether a room is habitable. That is the California Residential Code, and it sets floors that apply inside an ADU just as they do in any other dwelling:
- Habitable rooms: at least 70 square feet. Kitchens are excepted.
- At least 7 feet in any horizontal dimension. A long, narrow room can clear the 70-square-foot area and still fail this one.
- A ceiling of at least 7 feet over habitable space and hallways; bathrooms, toilet rooms and laundry rooms may come down to 6 feet 8 inches.
R312.1 Minimum area. Habitable rooms shall have a floor area of not less than 70 square feet (6.5 m²).
Exception: Kitchens.
R312.2 Minimum dimensions. Habitable rooms shall be not less than 7 feet (2134 mm) in any horizontal dimension.
R313.1 Minimum height. Habitable space, hallways and portions of basements containing these spaces shall have a ceiling height of not less than 7 feet (2134 mm). Bathrooms, toilet rooms and laundry rooms shall have a ceiling height of not less than 6 feet 8 inches (2032 mm).
(2025 California Residential Code)
Which building code applies depends on the structure. An ADU built within or beside a single-family home is constructed under the Residential Code. One created inside a larger multifamily building falls under the California Building Code, which sets its own floor: 190 square feet of habitable space for a dwelling unit, with at least one room of 120 square feet.
What this means in practice
The two codes answer different questions, and both answers hold at the same time:
- Can San Francisco refuse your ADU for being too small? No. Section 207.2(e) bars a size minimum that would block an ADU of up to 800 square feet.
- Can you put a 40-square-foot bedroom inside it? No — not because of the Planning Code, but because R312.1 requires a habitable room to be 70 square feet.
A 500-square-foot JADU has the same rooms to fit into less space, which is where the 7-foot dimension rule tends to bite first. Sleeping lofts are treated separately: Section R315.2 requires a sleeping loft's floor area to be less than 70 square feet, and allows a ceiling above 7 feet over no more than half of it.
Code references: Section 207.2(e), 2025 San Francisco Planning Code · R312.1, R312.2, R313.1 and R315.2, 2025 California Residential Code · 1208.3 and 1208.4, 2025 California Building Code.
