Fast, Reliable New Detached ADU Across San Francisco
Building a new detached ADU in San Francisco means working through a permitting process unlike anywhere else in the Bay Area. Shadow analyses, Soft Story Retrofit flags, historic district review, party-wall notices. Most of these obligations surface only after you’ve paid for drawings, and each one can stall a project for months or add tens of thousands of dollars. Since 2015, our New Detached ADU team has designed, permitted, and built more than 900 backyard units, and every single one came with a written price before the first drawing was produced. If you’re weighing a detached ADU on a San Francisco lot, call (971) 497-2402 and we’ll walk you through the specific permit path for your address.
Why Ellery ADU Studio Is San Francisco’s Preferred New Detached ADU Company
We’re a design-build studio, which means the drawings, the permit set, and the construction are one contract at one written price. Nobody blames the architect. Nobody blames the builder. Under Haven Standard Clause 1, the scope and price are locked in writing before work starts, and under the 365-Day Done Right Promise, if the finished ADU isn’t built to the permitted drawings, we make it right. In writing. Before the project begins.
San Francisco homeowners work with us because we check the city’s Soft Story Retrofit database before we price a job, not after the Department of Building Inspection flags it. We know which rear yards in the Sunset or Richmond sit on Bay Mud with undocumented fill. We know that a detached ADU over 12 feet tall in RH-1 or RH-2 zoning triggers a shadow study under Planning Code Section 295, and we know which districts pass that study without issue and which ones don’t. Nadia Ellery founded the studio the year California’s ADU permitting landscape shifted. She built the practice around the permit set as the core product, and that’s why our San Francisco projects clear plan review with fewer resubmittals than the city average.
Our New Detached ADU Services in San Francisco
A detached ADU on a tight San Francisco lot is a different animal than one on a flat East Bay parcel. Staging, crane access, party-wall rules, and work-hour restrictions all change the math. Here’s what we build, and how each service works in San Francisco specifically.
Custom Built ADU
A stick-built custom ADU gives you full control over the roofline, which matters here because the roofline is exactly what a shadow analysis measures. We design the structure to pass Section 295 review, not just to look good from the kitchen window. Most custom detached ADUs in San Francisco run $380,000 to $520,000 all-in, drawings through final inspection. The range moves based on soil conditions, foundation type, and whether the lot requires a street-occupation permit for crane access. Every quote is written and fixed before work starts. No door-side upsells, no scope creep. That’s Haven Standard Clause 5.
Prefab ADU Installation
Prefab works well on San Francisco rear lots if you plan the delivery day around the city’s street-parking permit windows. We specify and coordinate Dvele and Mighty Buildings systems within the same single contract, which means the module arrives to a foundation we’ve already prepared to manufacturer spec. A prefab detached ADU in San Francisco typically runs $280,000 to $420,000 complete, including site prep, delivery, set, and utility hookups. The big variable on tight lots is crane access: if the crane can’t sit on the street without a full lane closure, the SFMTA permit jumps from roughly $50 to several hundred dollars per day.
Modular ADU
Modular construction in San Francisco often runs through the same prefab factories but with panelized or volumetric components assembled on a prepared slab. We’ve coordinated Cover and Abodu systems here, and we’ve learned which ones clear DBI plan review fastest. A 1-bed modular detached ADU in San Francisco generally lands between $320,000 and $450,000, depending on whether the lot has rear access for the delivery trailer or needs a crane with a long reach. Modular’s advantage is schedule: the structure goes up in a week instead of four months, which matters when you’re paying San Francisco construction labor rates and dealing with neighbor noise complaints.
Studio ADU
A studio detached ADU is San Francisco’s most common backyard build, and the least expensive path to a rentable unit. A code-minimum studio around 400 square feet typically runs $250,000 to $340,000 in San Francisco, drawings through final. That range assumes a flat-ish rear yard, no historic district review, and no Soft Story complications on the main house. We price every studio with a written line-item scope, so you can see exactly what the slab, walls, roof, kitchen, bath, and tie-ins cost before you sign anything.
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.
Trusted Brands We Service in San Francisco
We don’t resell prefab units or take a markup on manufacturer pricing. Ellery ADU Studio specifies and coordinates systems from Dvele, Mighty Buildings, and Cover within the same single contract that covers your permit set and foundation work. That means one written price, one warranty, and one point of accountability. If the factory’s panel arrives out of square, we deal with it. If the architectural drawings don’t match the module’s connection points, we catch it before the crane is scheduled. For San Francisco homeowners, that coordination is the entire difference between a prefab ADU that closes out in six months and one that sits on a trailer in Marin while the city asks for another revision.
Common New Detached ADU Problems We See in San Francisco Homes
- Buying the prefab unit before running the permit check. Homeowners order a module, then discover their backyard is in a historic district where the SF Planning Department requires a Certificate of Appropriateness review that takes 90-plus days and may force a different exterior cladding. Now the unit sits in storage while the permit clock runs. We run the historic district and Soft Story database checks before any design work starts.
- Underestimating excavation on Bay Mud lots. San Francisco’s rear yards, especially in the Sunset and parts of the Mission, hold four or more feet of undocumented fill over compressible Bay Mud. The crane mat and mini-excavator need a street-occupation permit, which adds $3,000 to $8,000 before ground breaks. Our site assessments flag this in the first written scope.
- Ignoring the party-wall notice. A detached ADU built within three feet of the property line triggers a mandatory neighbor notification in San Francisco and a 15-day appeal window. One neighbor who objects to the roofline can stall the project for months. We draft and file the notice early, and we design rooflines that shadow studies and neighbors can both live with.
- Condensation and moisture intrusion in fog-belt districts. The Outer Sunset and Outer Richmond sit in persistent summer fog, which means daily condensation on slabs and stem walls. A slab poured without a vapor barrier becomes a permanent damp problem inside a finished ADU. Our standard detail includes a Stego vapor barrier and rigid mineral wool under every slab in these neighborhoods, because we’ve pulled up enough wet flooring in this city to know better.
Pricing for New Detached ADU in San Francisco, CA
| Service | Typical San Francisco Range | What Moves the Number |
|---|---|---|
| Studio detached ADU (approx. 400 sf) | $250,000 - $340,000 | Soil condition, rear access, historic review |
| Prefab detached ADU (1-bed) | $280,000 - $420,000 | Crane access, SFMTA street permit, foundation prep |
| Modular detached ADU (1-bed) | $320,000 - $450,000 | Delivery route, panel set, finish level |
| Custom built detached ADU (1-2 bed) | $380,000 - $520,000 | Roofline complexity, shadow study, site constraints |
These are all-in figures, drawings through final inspection, based on what we’ve built in San Francisco over the past nine years. They assume a typical rear lot with reasonable access and no seismic retrofit obligations on the main house. A Soft Story flag on your existing building can add $40,000 to $80,000 in seismic upgrade work before the ADU can be finaled. A shadow analysis requirement under Section 295 adds roughly $4,000 to $7,000 for the study and any roof redesign it forces. Every quote we issue is a written price under Haven Standard Clause 1. Call (971) 497-2402 and we’ll produce one for your address.
Serving San Francisco and the Surrounding Bay Area
Our design and scheduling operations run from our Bay Area office, and our crews serve San Francisco neighborhoods daily. We also take on detached ADU projects in Daly City, South San Francisco, Alameda, and Berkeley. If you’re just outside the city limits and wondering whether your lot qualifies, call us and we’ll run the same zoning and soil checks we run for our San Francisco clients. You can learn more about our local coverage on our New Detached ADU in San Francisco page.
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 - New Detached ADU in San Francisco
Yes, but expect a Certificate of Appropriateness review that takes 90 days or longer. The Planning Department may require exterior cladding, window proportions, or a roofline that matches the district’s character, even if your unit is in the rear yard and barely visible from the street. We prepare the review package alongside the building permit set so both tracks run simultaneously. Call (971) 497-2402 and we’ll check whether your address falls inside a district boundary before you spend a dollar on design.
If your building is flagged under Chapter 34B and hasn’t completed its retrofit, the ADU permit application will surface that open compliance obligation. You’ll be required to complete a Tier 3 or Tier 4 seismic upgrade, which typically costs $40,000 to $80,000, before the ADU can be finaled. We check the Soft Story database as part of our initial site assessment, so this never comes as a surprise midway through design.
Construction noise is prohibited between 8:00 p.m. and 7:00 a.m. on weekdays, and before 8:00 a.m. on weekends. San Francisco also enforces a 15-day neighbor appeal window when a structure is built within three feet of a property line. We sequence our noise-heavy work, like demolition and concrete cuts, inside the permitted hours and we keep neighbors informed with a written notice posted before work begins. It doesn’t eliminate complaints, but it does keep them out of DBI’s inbox.
Any new detached structure over 12 feet tall in an RH-1 or RH-2 zoning district triggers a shadow analysis under Planning Code Section 295. The study measures the shadow your new ADU casts onto any open space, public or private, between 9:00 a.m. and 3:00 p.m. In foggy Sunset and Richmond districts, this usually passes without issue. On a south-facing Noe Valley slope, a single gable can kill the permit. The study and any resulting roof redesign typically add $4,000 to $7,000 to the project.
The Outer Sunset sits in San Francisco’s persistent summer fog belt. Daily condensation forms on slabs and stem walls, and any foundation poured without a proper vapor barrier will wick that moisture into the finished floor assembly for years. East Bay cities get far less marine fog and far more sun. Our standard Outer Sunset detail includes a Stego vapor barrier under the slab and rigid mineral wool at the perimeter, plus mechanical ventilation sized for high-humidity months. It adds $6,000 to $12,000 to the foundation line item, and it prevents a chronic moisture problem that costs far more to remediate later.
Written by Nadia Ellery, Owner at Ellery ADU Studio, serving San Francisco since 2015.