Building an ADU in San Francisco is one of the best uses of square footage in a city that has almost none to spare — and one of the trickiest to execute, which is why owners bring in a contractor who has done it before. Zen Construction (CSLB #1041370) designs, permits, and builds accessory dwelling units across the city: garden cottages in deep Sunset lots, ground-floor infill units under Edwardian flats, and garage conversions in Bernal and the Excelsior. Eighteen years in, we run our own crews and handle the entire DBI process ourselves.
The payoff is real. A legal unit in San Francisco commands some of the highest rents in the country, and a well-built ADU adds long-term value whether it houses a tenant, a parent, or a home office with a kitchen. Start with a free feasibility estimate at /custom — we'll tell you honestly whether your lot and building can carry a unit worth building.
Ways to add an ADU in San Francisco
San Francisco's building patterns create ADU opportunities that don't exist in the suburbs. The most common paths we build:
- Ground-floor infill — converting garage, storage, or unfinished space under an existing house or flats into a unit. This is the signature SF ADU: the structure exists, the ceiling height question decides everything, and seismic strengthening of the soft story often gets bundled in.
- Garage conversions — freestanding or attached garages in Bernal Heights, the Excelsior, and the Outer Sunset convert well, typically starting around $120k depending on utilities and foundation condition.
- Detached garden units — deep lots in the Sunset and Richmond can take a backyard cottage. Detached new-build ADUs in the Bay Area run $250k–450k depending on size and site, and San Francisco's access constraints put most projects toward the upper half.
- JADUs — junior units up to 500 sq ft carved out of the existing home, the lightest-touch option.
Permits: state law, the local overlay, and DBI
California law requires ministerial approval of code-compliant ADUs — no discretionary hearing, no neighbor veto, and a 60-day review clock once the application is complete. San Francisco layers its own programs on top, including both state-law units and a local program with different trade-offs, and the right choice depends on your building and goals; we walk you through it in plain English. Plans still route through DBI and Planning, and in our experience completeness is everything: survey-accurate site plans, Title 24 energy docs, and fire-separation details answered before the checker asks.
Two SF-specific realities we plan around from day one. First, units in multifamily buildings can fall under rent control depending on which program they're permitted through — a decision that matters if you intend to rent. Second, utility capacity: older buildings often need electrical service upgrades to feed a new all-electric unit, and we scope that early, not after approval.
Building on San Francisco lots: hills, height, and access
The physical challenges here are unlike anywhere else we build. Backyards are usually reachable only through the house or a shared side passage, so materials move by hand — we plan demolition and concrete pours around that, and it's a real cost line, not an afterthought. Bernal Heights and Glen Park sites often slope hard, which means engineered foundations, retaining considerations, and drainage done properly, because water moving downhill through the neighbor's yard becomes your problem fast.
Fog-belt construction has its own rules too. In the Sunset and Richmond we detail ADUs against marine moisture: rainscreen-minded siding assemblies, generous mechanical ventilation, and windows specified for salt air. A garden cottage that ignores the fog will show it within five years; ours don't.
What an ADU costs and returns in this city
Typical ranges, not quotes: garage and ground-floor conversions from roughly $120k when the shell is sound, with seismic and utility upgrades adding scope in older buildings; detached new-build garden units $250k–450k across the Bay Area, with San Francisco access and site conditions usually landing projects in the upper portion of that band. Against that, San Francisco one-bedroom rents make the income math stronger here than almost anywhere we work, and financing is available to spread the build cost against future rent.
We give you a line-item budget after a free site visit, and we'll be direct if your lot doesn't pencil — about one visit in five ends with us advising the owner to wait or to change approach, and we'd rather earn that trust than sell a marginal project.
One team from sketch to keys
ADU projects fail in the gaps between designer, expediter, and builder. We removed the gaps: Zen Construction produces the plans, files with DBI, manages the 60-day clock and any completeness responses, then builds with our own crews — foundation, framing, electrical, plumbing, and finishes — with permits inspected through to a legal certificate of final completion. You get weekly photo updates from the first sawcut to the last cabinet pull, and you can see finished units in our portfolio. Every project starts with a free in-home consultation and written estimate.
Neighborhoods we serve in San Francisco
Our San Francisco ADU work concentrates where the lots allow it: ground-floor infill units under flats in the Mission and Richmond District, garage conversions in Bernal Heights and the Excelsior, and detached garden cottages on the deep parcels of the Outer Sunset. In Noe Valley and Glen Park we regularly combine an ADU with seismic soft-story strengthening, and in Pacific Heights the typical project is a polished ground-level suite for family or staff rather than a rental.
Reviews from San Francisco and nearby
Tiny Sunset kitchen, three windows, no room for error. They measured twice and built to the millimetre. Getting cabinets up a narrow staircase without marking a single wall impressed me more than anything.
Coastal kitchen built around the big window we refused to give up. They redesigned for the light instead of building over it — open shelving, quartz, tile to the ceiling. I still take pictures of it.
I was nervous about hiring anyone after a bad experience years ago. Written scope, a schedule I could actually read, and photos every week while I was travelling. This is how it should be done.
Recent work you can price
$15,000 – $25,000
$18,000 – $30,000
$22,000 – $36,000
ADU Construction in San Francisco — FAQ
How long does ADU approval take in San Francisco?
State law gives the city 60 days to act on a complete ADU application. The practical timeline depends on how quickly the application is deemed complete and how you respond to plan-check comments. In our experience, well-prepared San Francisco ADU permits typically resolve in a few months; incomplete submittals are what stretch to a year. We manage the clock and the responses for you.
How much does an ADU cost in San Francisco?
As typical ranges: converting an existing garage or ground floor starts around $120k when the structure is sound, and detached new-build garden units run $250k–450k in the Bay Area, with SF projects usually in the upper half because of access and site conditions. Utility upgrades and seismic work are the common adders. A free site visit gets you a line-item budget.
Can I build an ADU under my existing flats or house?
Often yes — ground-floor and garage-level infill is the most common San Francisco ADU. The deciding factors are ceiling height, utility capacity, and whether the level needs seismic strengthening, which can be bundled into the project. We check all three at a free feasibility visit and tell you plainly whether the space can become a legal unit.
Will my San Francisco ADU be rent-controlled?
It depends on the approval path and the building. Units permitted through certain local programs in multifamily buildings can be subject to rent control, while state-law units generally are not. This choice is one of the most consequential decisions in an SF ADU project, so we map out both paths and their trade-offs before drawings start, in plain language.
My backyard is only reachable through the house. Can you still build?
Yes — most San Francisco garden ADUs are built exactly that way. Materials and debris move through the building or a side passage by hand, so we protect floors and walls, sequence deliveries tightly, and budget the hand-carry labor honestly up front. It adds cost versus a suburban lot with driveway access, and our estimates say so explicitly.
Do I lose my garage parking if I convert it?
State ADU law prevents the city from requiring you to replace parking spaces lost to an ADU conversion in most circumstances. Whether giving up the garage is worth it is a personal call — in neighborhoods with easy street parking like the Outer Sunset, most owners say yes; on crowded Bernal streets some choose a garden unit instead. We'll talk it through honestly.
Do you handle the plans and permits, or just construction?
Everything. We produce the architectural plans, structural engineering, and Title 24 documentation, file with DBI and Planning, respond to plan-check comments, and then build the unit with our own crews through final inspection. One contract, one responsible party, weekly photo updates. That single-team structure is why our timelines hold and our clients aren't refereeing between a designer and a builder.