What Is an ADU?
An Accessory Dwelling Unit (ADU) is a secondary housing unit on a single-family residential lot. In San Francisco, ADUs go by many names — in-law unit, granny flat, backyard cottage, garden apartment. Whatever you call it, an ADU is a fully independent living space with its own kitchen, bathroom, entrance, and sleeping area.
California's ADU laws (AB 881, SB 13, AB 68) have dramatically expanded homeowners' rights to build ADUs — overriding many local restrictions that previously made them nearly impossible in cities like San Francisco.
Types of ADUs You Can Build in San Francisco
Detached ADU
A standalone structure in your backyard, side yard, or rear yard. Can be up to 1,200 square feet regardless of your lot size. This is the most flexible option and typically offers the best rental income potential.Garage Conversion
Convert your existing garage into a finished living space. Often the most cost-effective option because the structure already exists. You are NOT required to replace the lost parking space.Basement Conversion
Convert unused basement space into a legal dwelling unit. Requires proper ceiling height (minimum 7 feet), egress windows, ventilation, and waterproofing. Common in SF's older homes with unfinished basements.Junior ADU (JADU)
A unit up to 500 square feet created within your existing home — for example, converting a bedroom with a separate entrance and kitchenette. JADUs are often the fastest and cheapest to build. You can build a JADU AND a detached ADU on the same lot.How Much Does an ADU Cost in San Francisco?
Real numbers from the SF market:
What's Included in These Costs
- Architectural design and engineering
- DBI permit fees and plan review
- Site work and foundation
- Framing, plumbing, electrical, HVAC
- Insulation, drywall, paint
- Kitchen and bathroom fixtures
- Flooring, doors, windows
- Title 24 energy compliance
- Final inspections and Certificate of Occupancy
What Drives ADU Costs Up
- Site conditions: Sloped lots, limited access, and poor soil conditions increase foundation and site work costs.
- Utility connections: Running new sewer, water, and electrical service to a detached ADU can add $15,000–$40,000 depending on distance and existing infrastructure.
- Finishes: Builder-grade finishes vs. high-end finishes can swing costs by 30–50%.
- Structural complexity: Two-story ADUs, complex rooflines, and custom designs cost more than simple rectangular floor plans.
The SF DBI Permit Process for ADUs
San Francisco has streamlined its ADU permitting, but it's still a multi-step process:
Step 1: Pre-Application Research (1–2 weeks) Check your lot's zoning, setbacks, and utility access. Determine which type and size of ADU is feasible.
Step 2: Design & Engineering (4–8 weeks) Architectural plans, structural engineering, and Title 24 energy calculations — all prepared for DBI submittal.
Step 3: DBI Plan Review (8–16 weeks) Submit your plans to DBI for review. Expect plan check comments and at least one round of revisions. ADU projects typically get expedited review — but "expedited" in SF still means 2–4 months.
Step 4: Permit Issuance Once plans are approved, your building permit is issued and construction can begin.
Step 5: Construction Inspections Multiple inspections throughout construction — foundation, framing, rough plumbing/electrical, insulation, and final.
Step 6: Certificate of Occupancy After final inspection, you receive a Certificate of Occupancy — the legal document that makes your ADU a permitted dwelling unit.
Pro Tips for Faster Permitting
- Submit complete, code-compliant plans the first time. Incomplete submittals get sent back and restart the queue.
- Use standard details and proven floor plans. Custom everything takes longer to review.
- Respond to plan check comments within 2 weeks. Don't let your file go stale.
- Work with a contractor who has been through the DBI process before. Experience with the department saves months.
ADU Rental Income in San Francisco
Current market rental rates for ADUs in San Francisco:
- Studio/efficiency: $1,800 – $2,500/month
- 1-bedroom: $2,200 – $3,500/month
- 2-bedroom: $3,000 – $4,500/month
Important: ADUs in San Francisco are subject to rent control and just-cause eviction protections. Consult a property management professional or attorney for current tenant regulations.
Will an ADU Increase My Property Value?
Yes — significantly. Appraisers value ADUs based on the income they generate and the additional living space they provide. In San Francisco's market, a fully permitted ADU typically adds $200,000–$400,000+ to property value.
Key factors that maximize ADU value:
- Full permit and Certificate of Occupancy (unpermitted units are a liability, not an asset)
- Separate utility meters
- Private entrance and outdoor space
- Quality finishes that match the neighborhood
- Code-compliant kitchen and bathroom
Is an ADU Right for You?
An ADU makes sense if you:
- Want rental income to offset your mortgage or supplement retirement
- Need space for a family member (aging parent, adult child)
- Want a home office or studio separate from your main home
- Plan to stay in your home long-term and want to maximize property value
- Have underutilized space (unused garage, unfinished basement, large backyard)
Next Steps
The first step is a feasibility assessment. We visit your property, evaluate your lot, review zoning and setback requirements, and give you a clear answer on what type and size of ADU you can build — and what it will cost.
No obligation. No pressure. Just the information you need to make a smart decision.