Creating an Accessory Dwelling Unit (ADU) in San Francisco
San Francisco is increasingly embracing accessory dwelling unit (ADU)s as a way to increase housing supply and provide flexible living arrangements. Whether you're converting a basement, building a detached ADU, or creating an in-law suite, this guide walks you through every step of the permit process.
Important: Working without required permits in San Francisco can result in stop-work orders, fines, mandatory demolition of completed work, and complications when selling your property. Requirements vary by property — your zoning, lot coverage, and setbacks all affect the answer.
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Overview
An accessory dwelling unit (ADU) is a secondary housing unit on a single-family lot. ADUs come in several forms: basement conversions, garage conversions, attached additions, or detached backyard units. San Francisco has been expanding ADU regulations to increase housing supply.
An ADU must meet International Building Code / International Residential Code requirements for fire safety, structural integrity, ceiling height, egress, ventilation, and plumbing. Getting the proper permits ensures your ADU is legal, safe, and insurable.
Do You Need a Permit?
Yes, always. Creating an accessory dwelling unit (ADU) requires a building permit from the San Francisco Department of Buildings. This involves a change of use or new construction and triggers a full code review.
You will need permits for:
- Building permit (for the ADU construction or conversion)
- Plumbing permit (for new or modified plumbing)
- Electrical permit
- HVAC modifications (if applicable)
Some cities also require a separate ADU application or planning approval in addition to the building permit.
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The remaining 6 sections — including step-by-step process, required documents, inspections, and cost breakdowns — depend on your specific property and zoning.
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San Francisco-Specific Requirements
San Francisco's ADU requirements include:
- Zoning: ADU regulations vary by zoning district. Many cities now allow ADUs by right in single-family zones. PermitPaths checks your specific zoning automatically.
- Fire Separation: A fire separation with a minimum 1-hour fire resistance rating is required between the ADU and the primary dwelling (for attached/internal ADUs).
- Separate Entrance: The ADU must have its own entrance.
- Egress Windows: Every bedroom must have an egress window meeting minimum size requirements (5.7 sq ft opening, minimum 24 inches high × 20 inches wide).
- Ceiling Height: Minimum 2.13 m (7 feet) clear height for habitable rooms.
- Smoke and CO Alarms: Smoke alarms and CO alarms are required per the IBC/IRC.
- Kitchen and Bathroom: The ADU must have its own kitchen and bathroom facilities.
- Size Limits: Many jurisdictions cap ADU size (typically 800–1,200 sq ft). Check San Francisco's specific limits.
Step-by-Step Process
- Check zoning eligibility — Verify your property allows an ADU. Use PermitPaths for an instant zoning check.
- Hire professionals — You'll likely need an architect or licensed general contractor for drawings.
- Prepare detailed plans — Floor plans, fire separation details, egress windows, plumbing layout, electrical layout, and HVAC.
- Submit permit application — Apply to the San Francisco Department of Buildings with all required drawings and documents.
- Pay fees — ADU permits can cost $250–$3,000+ USD depending on the scope.
- Wait for review — Expect 3–6 weeks for review. The plans examiner may request revisions.
- Construction — Build according to approved plans.
- Schedule inspections — Multiple inspections are required: framing, plumbing rough-in, electrical rough-in, insulation, and final.
- Final inspection and occupancy — Once all inspections pass, you receive your certificate of occupancy.
Cost Breakdown
- Building permit fee: $250–$3,000+ USD
- Architectural/design drawings: $2,000–$8,000
- Structural engineer (if needed): $500–$3,000
- Plumbing: $5,000–$15,000
- Electrical: $3,000–$10,000
- Fire separation (for attached ADUs): $2,000–$5,000
- General construction: $20,000–$60,000+
Total cost for an ADU in San Francisco typically ranges from $50,000–$150,000+ USD. Rental income or increased property value can provide significant return on investment.
Common Mistakes
- Not checking zoning first: ADU regulations vary significantly by zoning district. Check before investing in plans.
- Inadequate fire separation: The fire separation between the ADU and primary dwelling is heavily scrutinized during inspections.
- Exceeding size limits: Many jurisdictions cap ADU size. Exceeding the limit requires a variance or redesign.
- Ignoring parking requirements: Some jurisdictions require additional parking for ADUs, though many have eliminated this requirement.
- Not planning for utilities: Water, sewer, gas, and electrical connections for the ADU need to be planned carefully.
Required Documents
- Completed ADU application form
- Floor plans — Existing and proposed, showing all units on the lot
- Fire separation details — For attached or internal ADUs
- Site plan — Showing ADU location, setbacks, entrances, parking
- Utility connections plan — Water, sewer, electrical, gas
- Plumbing layout — All fixtures, drainage, water supply
- Electrical plan — Panel locations, circuits, smoke/CO alarm layout
- Structural drawings — If any structural modifications needed
Pro Tips
- Check state and local ADU laws: Many states have passed laws preempting local restrictions on ADUs. Know your rights.
- Consider prefab ADUs: Pre-fabricated ADU kits can significantly reduce construction time and cost.
- Plan for parking: Even if not required, having parking available for the ADU tenant is practical.
- Get multiple contractor quotes: ADU projects are complex. Get at least three detailed quotes.
- Use PermitPaths: Our assessment tool checks your address for zoning eligibility and other factors that affect ADU feasibility in San Francisco.
Frequently Asked Questions
Can I build an ADU in San Francisco?
Many residential properties in San Francisco now allow ADUs. Regulations vary by zoning district. Check your specific property's eligibility with PermitPaths.
How much does it cost to build an ADU in San Francisco?
A typical ADU in San Francisco costs $50,000–$150,000+ USD including permits ($250–$3,000+), design, construction, plumbing, electrical, and finishing work.
How long does it take to get an ADU permit in San Francisco?
The permit review typically takes 3–6 weeks. Construction adds several months. Plan for 8–14 months from design to completion for a full ADU project.
What is the maximum size for an ADU in San Francisco?
ADU size limits vary by jurisdiction. Many cities cap ADUs at 800–1,200 square feet. Check San Francisco's specific regulations for your zoning district.
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