ADU cost in San Francisco
A garage conversion ADU typically costs $120,000 to $250,000. A detached new-construction ADU generally costs $300,000 to $450,000 or more. Prefab options often fall between $150,000 and $350,000, depending on size and finish.
Per square foot, San Francisco runs roughly $300 to $520 for conversions and $400 to $700 or more for detached new construction. These figures cover typical, well-planned projects. A smaller, simpler ADU can land at the lower end, and a highly customized unit or a difficult site can exceed the ranges.
What is an ADU?
An ADU is a secondary, independent living unit on the same property as a primary home, with its own kitchen, bathroom, and entrance.
California law has made ADUs easier to build in recent years by streamlining approvals and limiting how much cities can restrict them. San Francisco applies its own local rules on top of the state baseline, so local cost and process knowledge matters.
San Francisco ADU cost by type
The type you build is the biggest single factor in total cost.
| ADU type | Typical cost in San Francisco | What drives it |
| Garage conversion | $120,000 to $250,000 | Reuses the existing foundation, walls, and roof |
| Attached ADU | Between a conversion and a detached unit | How much new square footage you add versus how much structure you reuse |
| Detached ADU | $300,000 to $450,000 or more | Ground-up construction, a new foundation, and full utility connections |
| Prefab ADU | $150,000 to $350,000 | Factory-built unit, with site work still done locally |
| Junior ADU | Typically the lowest | Built within existing walls, with little foundation or structural work |
Garage conversion ADU cost
The $120,000 to $250,000 range assumes a standard two-car garage converted to a one-bedroom or studio unit, with new plumbing, electrical, and finishes. A garage already suited to conversion lands toward the low end. Significant structural repair, or a raised floor to meet code, pushes the cost up.
Attached ADU cost
An attached ADU, built onto or within the existing home, generally costs between a garage conversion and a detached unit. It shares some existing structure but still needs meaningful new construction.
It makes sense where there is no garage to convert or where the home’s layout supports a connected unit.
Detached ADU cost
A standalone backyard unit needs full ground-up construction, a new foundation, and complete utility connections. It is generally the most expensive type. It also offers the most design flexibility and the most separation from the main house, which suits privacy and rental appeal.
Prefab ADU cost
A prefab ADU is built off-site and installed on your property. It often offers more predictable pricing and faster timelines than custom construction, and factory production reduces exposure to weather delays and some labor shortages.
Foundation, utility connections, and final assembly still happen on site, so a prefab unit still carries San Francisco’s local costs.
Junior ADU cost
A junior ADU is created within the walls of the main house and capped at a smaller size. It is typically the least expensive type because it avoids most new foundation and structural work.
It often converts an existing bedroom into a smaller independent unit, which may share a bathroom or entrance with the main house.
ADU cost per square foot
Per-square-foot pricing lets you compare options and bids, because total cost scales with unit size.
Garage conversions run roughly $300 to $520 per square foot. Attached and detached new construction run roughly $400 to $700 or more, among the highest ranges in California. Labor scarcity, strict local building requirements, and the cost of doing business as a contractor in San Francisco drive that premium.
Full ADU cost breakdown: where the money goes
Knowing the categories lets you check a contractor’s bid line by line.
| Category | What it covers |
| Soft costs: design | Architectural design and custom plans before construction starts. Problems caught on paper cost less than problems found mid-construction. |
| Soft costs: consultants | Planning and permitting consultants, who can help navigate San Francisco’s ADU requirements and sometimes save enough review time to offset their fee. |
| Building permit | Generally $5,000 to $20,000, depending on scope and whether you use pre-approved plans. |
| Impact fees | Often waived under California law for ADUs under 750 square feet. Larger units may still pay, depending on jurisdiction. |
| Utility connection fees | New water, sewer, and electrical hookups. Highest for detached units that need new runs from the street or main house. |
| Site prep | Grading, excavation, and foundation work. Varies with slope, soil, and existing structures on the lot. |
| Hard construction costs | Framing, roofing, systems, and finishes. Usually the largest category. |
| Utilities | HVAC, electrical panel, and plumbing sized for a fully independent unit. |
Confirm your unit’s impact fee eligibility early in planning.
If you might later switch the unit from a rental to family space, consider spending a little more on utilities and systems up front. Retrofitting them after construction is far more disruptive.
Cost drivers that shape your ADU budget
Several factors explain why two similar ADUs can carry very different prices.
| Driver | Effect on cost |
| Square footage | A larger ADU costs more in total, even at a similar per-square-foot rate. |
| Floor plan and layout | A simple, efficient plan costs less than unusual room shapes or extensive custom millwork. |
| Kitchen | One of the most expensive rooms per square foot, because of plumbing, electrical, cabinetry, and appliances. |
| Bathroom | Similarly high per square foot, driven by plumbing, waterproofing, fixtures, and tile. |
| Custom vs. pre-approved plan | A custom plan costs more in design fees and review time. A pre-approved plan can save money and months of permitting time in San Francisco. |
| Site conditions | Slope, soil, and existing structures add cost, especially on hillside lots where foundation engineering alone can move the budget. |
| Number of bedrooms | More bedrooms mean a larger unit and a higher total, even at the same finish level. |
| Utility connection distance | A detached unit far from existing hookups costs more to connect. |
Hidden costs homeowners often miss
Property taxes after construction
The added square footage is usually reassessed, so property taxes typically rise after construction. This ongoing cost lasts as long as you own the property.
Utility connection surprises
If existing service cannot support a second independent unit, you may need an electrical panel upgrade or new dedicated service lines that were not in the original estimate.
Unexpected site prep
Poor soil or aging utility lines found once excavation begins are among the most common causes of ADU cost overruns, particularly on older San Francisco properties.
ADU cost examples by project type
These examples show how the ranges apply. Your numbers depend on your site, design, and finish level.
| Project | Where it typically lands |
| Two-car garage conversion, about 400 to 500 sq ft, one bedroom | Toward the middle of $120,000 to $250,000, with standard finishes and no major structural surprises |
| Detached backyard ADU, 500 to 600 sq ft, full kitchen and bathroom | Within $300,000 to $450,000, reflecting a new foundation and full utility connections |
| Prefab ADU on a flat, accessible lot | Toward the lower end of $150,000 to $350,000, because site prep and installation are more predictable |
| Junior ADU within existing walls | Meaningfully below the options above, because it avoids new foundation and major structural work |
| Attached ADU sharing one wall with the main house | Between a garage conversion and a detached unit, depending on how much new construction it requires |
Financing options for your ADU project
Settle financing before you choose an ADU type, because it affects your monthly costs and your project timeline.
Home equity loan
Borrowing against the equity in your primary home is one of the more common ways to fund an ADU, and it avoids a construction-specific loan.
Construction loan
A construction loan pays out in stages tied to construction milestones and often converts to permanent financing when the ADU is finished.
California state grants and programs
California has offered state grant programs for ADU construction, but availability and funding change. Confirm a program’s current status before you count on it in your budget.
Rental income and ROI considerations
Many homeowners build an ADU for rental income, and San Francisco’s rental market can make it a productive long-term investment. Compare expected rental income with your total ADU cost to estimate the payback period before you choose a project type.
A detached unit may rent for meaningfully more than a garage conversion, but the more expensive option is not always the better financial choice. Run the numbers for each, especially if the ADU is an investment property.
Permits and fees: what San Francisco requires
Permits and fees add cost and time to any ADU project. Permitting delays can raise financing and holding costs before you start building, and first-time ADU owners are often surprised by how much of the overall timeline permits consume.
Building permit process
ADUs follow the city’s standard review path, though state law requires a decision within 60 days for compliant applications. A complete, accurate application the first time moves faster than one that has to be resubmitted.
Permit costs and timeline
Permit costs generally run $5,000 to $20,000. The timeline depends on whether you use pre-approved plans and on how complex the project is. Pre-approved plans generally move faster and can lower total cost by avoiding extended review cycles.
Working with a contractor: getting accurate estimates
Real bids reflect your property and design in a way online ranges cannot. A guide like this one gives you realistic ranges, but only a detailed, site-specific bid from a local builder gives you your own number.
Getting multiple quotes
Get several quotes. ADU pricing commonly varies 20% to 40% between builders for the same project. Ask each contractor for a price per square foot alongside the total bid so you can compare them directly.
What a detailed estimate should include
A detailed estimate separates soft costs, permits and fees, site prep, hard construction costs, and utilities, so you can see where the money goes. Ask each contractor how they handle utility sizing and connections, because that line varies widely between bids.
A bid that looks cheap but leaves out major categories rarely stays cheap once construction starts.
California ADU cost context: how San Francisco compares
San Francisco ranks among the most expensive ADU markets in California, because of high labor costs, complex sites, and some of the state’s strictest building requirements. A cost range that looks reasonable for California can fall well short of a comparable San Francisco project.
Cost figures in national or statewide guides rarely reflect the local premium. When you compare quotes with numbers you find online, check whether those numbers were built for San Francisco or extrapolated from a broader California average.
ADU vs. home addition or remodel
An addition or a remodel can sometimes meet similar needs without a separate unit. An addition attached to the main house, with no kitchen or separate entrance, generally avoids some ADU-specific permitting and utility requirements, but it cannot produce the same rental income.
Remodeling existing space can sometimes add living area for less than any new construction, ADU included, when the existing structure and systems are in reasonable condition.
Rental income and full independence point toward an ADU. Extra family space without a separate unit may point toward an addition or remodel.
California ADU program basics
California’s statewide ADU program sets baseline rules every city must follow, including San Francisco: streamlined review timelines, limits on how much cities can restrict ADU size relative to lot size, and standardized parking rules. These rules make ADUs buildable on far more properties than older local codes allowed.
Knowing the baseline helps you tell which limits are San Francisco’s own choices and which apply statewide. Account for both layers when you start designing.
Key takeaways
- Garage conversion ADUs in San Francisco typically cost $120,000 to $250,000. Detached new construction generally costs $300,000 to $450,000 or more.
- Cost per square foot runs roughly $300 to $520 for conversions and $400 to $700 or more for new construction.
- Soft costs, permits, impact fees, utility connections, site prep, and hard construction costs all add to the total.
- Square footage, kitchen and bathroom finishes, custom versus pre-approved plans, and site conditions are the biggest drivers you can control.
- Property tax increases and unexpected site prep are common hidden costs to budget for.
- Several detailed quotes are the most reliable way to find the real cost for your property.
Get an ADU cost estimate for your San Francisco project
Talk to a local San Francisco ADU contractor early to get a detailed cost breakdown for your property, your ADU type, and your finish level. Ask about permits, budget contingencies, and how they structure a build from design through final inspection.
Use this guide as the starting point for that conversation, and let an itemized bid set the final budget.
