A free site visit, a check of what your lot allows and a written, line-item price.
Get your free estimateADU Company in San Francisco, CA
Adding an ADU in San Francisco means working with a city where the housing shortage is real, construction costs run high, and most homes were built before 1940. That combination shapes every project we take on here. You’ll deal with steep slopes, zero lot lines, soft-story retrofits, and a permit process that rewards homeowners who show up with a written plan. We’re Benson ADU San Francisco, and we build ADUs, home additions, and room additions across the city with one core promise: a written price before any work starts. Call (424) 328-5746 to talk through your project.
Why San Francisco Homes Are Different
San Francisco’s housing stock is dominated by pre-1940s wood-frame homes, many built on steep hillsides or packed tight against neighboring structures. That creates site constraints you won’t find in newer suburbs. A zero lot line means your ADU wall may sit directly on the property boundary, which changes how we handle setbacks – the required distance between a structure and the property line. Many older garages and basements also need seismic work before they can legally become living space, because the city requires structural upgrades when you change a building’s use.
The climate matters too. San Francisco’s fog, wind, and marine layer mean moisture management is not optional. A poorly detailed wall assembly in the Sunset will show rot within a few years. We spec weather-resistant barriers, proper flashing, and passive solar orientation as standard, not as upgrades. And in neighborhoods like the Sunset and Richmond, where sandy soil and a high water table put many garages at street level, a garage ADU often requires raising the floor above base flood elevation. That’s a San Francisco-specific cost driver most homeowners discover the hard way.
Our Main San Francisco Services
Most San Francisco homeowners reach out to us for one of three projects, each with its own dedicated page so you can dig into the specifics without wading through unrelated detail.
ADU Builders in San Francisco
An ADU is a self-contained dwelling unit with its own kitchen, bathroom, and entrance, built on the same lot as your primary home. In San Francisco, the most common paths are garage conversions, basement conversions, and detached backyard units. Garage conversions on the west side often trigger flood zone requirements that add foundation and elevation work. Detached units on sloped lots may need pier or caisson foundations instead of a simple slab. We build with prefab systems from brands like Plant Prefab and Boxabl to shorten on-site time, and we write the full price before demolition starts. See the full breakdown on our ADU Builders in San Francisco page.
Home Addition Contractor in San Francisco
A home addition extends your existing living space rather than creating a separate unit – think a larger kitchen, a new primary suite, or a family room that connects to the main house. San Francisco’s older wood-frame homes often hide surprises once walls come down: knob-and-tube wiring, undersized floor joists, or foundation cracks that need addressing before the addition can proceed. We include those contingencies in the written price instead of billing them as change orders later. For specifics on how we handle additions on San Francisco’s tight lots, visit our Home Addition Contractor in San Francisco page.
Room Addition Contractor in San Francisco
A room addition is a single-room project, usually a bedroom, home office, or exercise room. In San Francisco, the biggest constraint is often the lot itself. Many homes sit close to the property line, which limits horizontal expansion and pushes additions upward or into underused space above the garage. We’ll walk you through setback requirements and what’s buildable on your specific lot before you commit. See our Room Addition Contractor in San Francisco page for the full scope of this service here.
What happens when you call
- 1
A real person answersNo phone trees - you reach a local pro.
- 2
You get an upfront price rangeHonest numbers before anyone is dispatched.
- 3
A background-checked tech heads outLicensed & insured, dispatched right away.
- 4
You approve before work beginsNothing starts until you say go.
Brands We Service in San Francisco
We build with prefab and materials brands you can research yourself, including Plant Prefab, Boxabl, Tuff Shed, and James Hardie cladding. That means real spec sheets, third-party testing data, and no mystery products behind the drywall. See our brands page for the full lineup and what each system costs in San Francisco.
Pricing for ADU Company in San Francisco, CA
| Service | Typical range in San Francisco |
|---|---|
| ADU project cost (garage or basement conversion) | $180,000 – $350,000 |
| Detached ADU project | $250,000 – $450,000+ |
| Prefab ADU (studio, installed) | $95,000 – $200,000 |
| Prefab ADU (one-bedroom, installed) | $170,000 – $310,000 |
| Home addition (foundation to finish) | $300 – $550 per sq ft |
| Room addition (single room) | $80,000 – $200,000 |
| Garage conversion to ADU | $100,000 – $250,000 |
| Seismic retrofit (soft-story or foundation upgrade) | $30,000 – $100,000 |
| Design and permit package | $15,000 – $40,000 |
| Site prep, drainage, and foundation work | $20,000 – $70,000 |
What pushes prices up in San Francisco more than anything else is the site itself. Steep slopes, flood zone elevations, zero lot lines, and soft-story retrofits can each add tens of thousands to a project. That’s exactly why we give you a written price before work starts – not a verbal estimate that shifts once the permits come back.
Neighborhoods We Serve in San Francisco
We work across the entire city, from the foggy avenues of the Sunset and Richmond to the hillier terrain of Noe Valley, Bernal Heights, and Glen Park. Our crews know which neighborhoods trigger flood zone reviews and which lots need geotechnical reports before foundation design can begin. Typical response time for a callback after you reach out is within one business day, and a live person answers the phone around the clock.
- Sunset District
- Richmond District
- Noe Valley
- Bernal Heights
- Glen Park
Service Area – Cities Near San Francisco
While this page focuses on San Francisco itself, our Bay Area service area extends to nearby cities. We work regularly in Berkeley, CA, Albany, CA, Piedmont, CA, and Mill Valley, CA. Each city has its own permit quirks, and our team handles the paperwork for you.
Serving San Francisco, CA - Our Local Coverage Area
We’re based in the San Francisco area and know this community well. Use the map below to see our service coverage - if you’re nearby, we can almost certainly help.
FAQs About ADU Company in San Francisco
Most San Francisco ADU projects take 8 to 14 months from design to final inspection, with prefab systems running faster, often 6 to 9 months. Permitting at the city typically takes 2 to 4 months, and site constraints like slope work or flood zone review can add time. Call (424) 328-5746 for a realistic timeline on your specific lot.
Only if your property is part of a homeowners association. Under California state law, most HOAs cannot outright ban ADUs, but they can impose reasonable rules on design, parking, and construction hours. We help you identify what your HOA’s covenants actually allow before you spend money on plans.
After you sign your written agreement, we typically begin site work within 2 to 4 weeks, depending on permit status and materials lead time. Prefab systems from brands like Boxabl and Plant Prefab can shorten site work significantly, but city permits still set the pace. Call (424) 328-5746 to walk through your start date.
Ready to get a real number for your San Francisco ADU, addition, or room project? Call (424) 328-5746 to schedule your free estimate. Troy Eastman and our team will put the price in writing before anything gets built.
What happens when you call
- 1A real person answersNo phone trees - talk to a local adu pro.
- 2You get an upfront price rangeHonest numbers before anyone is dispatched. No surprises.
- 3We come out and measureLicensed & insured, at a time that suits you - the visit and the quote are both free.
- 4You get the price in writingLine-itemed, yours to keep, and nothing starts until you say go.
What San Francisco Customers Say
"Great build. Inspection delay, the county's fault, pushed things a week, but updates were clear."
- Soo-jin P."Garage conversion into a guest suite. I could see the permit status in the app, which made it painless."
- Rick F."Solid job. Cabinets arrived late but they adjusted the schedule."
- Eli K.
