ADUs and Older Buildings: Two San Francisco Special Cases

Chapter 12 of 12Part IV: Approvals and Permits

Two kinds of project in San Francisco follow rules that sit on top of the usual Planning and permit process. Accessory dwelling units have their own programs, one set by the state and one by the city, with very different review. Older buildings may be treated as historic resources, which adds a layer of design review to exterior work. Both are common in the city, and both reward hiring an architect who has done them before.

Part 1: Accessory dwelling units

An ADU is a second, smaller home on the same lot: a converted garage or basement, an addition or a separate backyard cottage. San Francisco Planning runs two programs side by side. Planning’s comparison chart, updated in August 2025, is the best single summary, and the points below come from it.

State ADUs

State ADUs follow California’s ADU law and Planning Code Section 207.2. Their big advantage is the process. Review is ministerial, with a 60-day timeframe from a complete application; there is no Section 311 neighborhood notice, no Discretionary Review and no review under the California Environmental Quality Act. Subjective design review is limited to properties on the California Register or designated under Article 10 or 11.

In exchange, the design must fit fixed standards. For a detached ADU on a single-family lot the chart lists:

• one ADU, which may be combined with a junior ADU and a converted ADU in some cases;
• up to 850 square feet for a studio or one-bedroom and up to 1,000 square feet for two or more bedrooms;
• a height of 16 feet, or 18 feet near major transit, with 2 more feet allowed to match the roof pitch of the main house;
• 4-foot setbacks from the side and rear lot lines, with an exception for rebuilding an existing structure in the same place and size;
• an independent entrance and a full kitchen, or a partial kitchen for an efficiency unit.

Local ADUs

Local ADUs follow Planning Code Section 207.1. They must meet the Planning Code, but waivers are available for rear yard, open space, exposure and density when the ADU is added to an existing building. The number allowed depends on how many units are already on the lot, with no limit for buildings doing mandatory or voluntary seismic upgrades. Local ADUs come with conditions the state program does not have, including limits on lots with recent no-fault evictions and, when waivers are granted on a lot with a rental unit, an agreement that puts the ADU under rent control.

	State ADU	Local ADU
Review	Ministerial, 60 days from complete application	Planning review; expansions may get neighborhood notice
Neighborhood notice and DR	None	Possible for expansions
Size and height	Fixed state limits	Based on zoning and buildable area
Waivers from Planning Code	Not needed; fixed standards	Available for several requirements
Number of ADUs	Usually one on a single-family lot	Depends on existing units; more with seismic upgrades

Owners must complete DBI’s ADU screening form, and impact fees depend on the ADU’s size and the number of existing units. You do not have to decide which program you fit before you start: Planning’s ADU staff and a knowledgeable architect can compare the options for your lot.

Part 2: Older and historic buildings

San Francisco Planning sorts properties into three categories for historic review. Category A properties are known historic resources. Category B properties are 45 years or older and have not been formally evaluated, which covers a large share of the city’s houses. Category C properties have been found not to be historic, or are younger than 45 years.

The category matters for design. Planning’s ADU chart states that Category A properties are subject to preservation review for all exterior work, Category B properties for exterior work visible from the public right-of-way, and Category C properties are not. Buildings designated as local landmarks under Article 10 of the Planning Code have an additional layer of review for exterior changes, and Article 11 covers conservation districts in the downtown core. Planning offers a Historic Resource Review, and says it responds within 45 days once a complete application is accepted.

What this means for hiring

• If your house is 45 years or older and the work shows from the street, ask candidates about their experience with historic review.
• Ask whether a Historic Resource Review early in design would save time later.
• Expect window and door replacements on a historic resource building to need in-house Planning review, as noted in Building Permits at DBI: Over-the-Counter, In-House and Site Permits.

Putting the handbook together

Whether your project is an ADU, an addition to an older house or a simple remodel, the order of this handbook holds: know what you need, choose carefully, put the agreement in writing, design with review in mind and then take the project through the city. If you skipped ahead, the start is here: Do You Need an Architect for Your San Francisco Project?.