What Will Your ADU Cost?
Get an instant San Diego ADU estimate — construction costs plus permit and impact fees for your city. Configure it your way and watch the numbers update live.
- Instant results — no email needed to see numbers
- Permit & impact fees for every San Diego County city
- Built from real project data, not national averages
Planning estimate, not a quote. Actual pricing depends on your site, plans, and finish selections — we’ll confirm real numbers after a site walk.
Construction Breakdown
Permits & Fees
City of San Diego
Pre-approved plan programs can cut plan-check fees roughly in half.
Planning-level estimates from published 2025–2026 fee schedules and regional surveys. Impact fees are waived statewide under 750 sq ft; school fees don't apply at 500 sq ft or under. Always verify with your jurisdiction — a free Casita site walk turns these into real numbers for your parcel.
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We'll email this breakdown with permit details for your jurisdiction — and a Casita specialist will follow up about a free site walk.
No spam — just your estimate and a real human follow-up.
What Happens Next
A calculator gets you in the right range. A site walk gets you a number you can plan around.
Get your range
Set the ADU type, size, finish level, and site conditions. The estimate updates live, with a construction breakdown and permit fees for your city.
Free site walk
We come to your property, look at access, utilities, grading, and setbacks — the things a calculator can't see — and tell you what's realistic.
Real numbers
You get a real proposal for your parcel and your plans. If it doesn't pencil, we'll tell you that too.
San Diego ADU Costs, Explained
What drives the number, what's included, and how the estimate becomes a real quote.
Expect roughly $250–$350 per square foot for new detached and attached ADU construction in San Diego County, and about $200–$290 per square foot for garage conversions, depending on finish level and site conditions. Smaller units cost more per square foot because kitchens, bathrooms, and utility connections are fixed costs spread over less area.
A garage conversion is usually the cheapest ADU because the foundation, roof, and walls already exist — in San Diego County they typically run $150,000–$215,000 versus $190,000–$250,000 for a new detached unit of similar size. Choosing a pre-approved plan and keeping the unit under 750 sq ft (which waives development impact fees statewide) also cuts cost.
Permit, plan-check, impact, school, and utility connection fees for a San Diego County ADU typically total $10,000–$35,000 and vary by city and unit size — a small garage conversion can come in under $10,000, while a 750+ sq ft detached unit in the City of San Diego can approach $35,000. California waives development impact fees for any ADU under 750 sq ft, and school fees do not apply to units of 500 sq ft or less. Casita's estimator prices fees for all 19 San Diego County jurisdictions (18 cities plus the unincorporated county) from published 2025–2026 fee schedules.
No — it is a planning estimate built from Casita's real San Diego project data, meant to put you in the right range before you commit to design. Actual pricing depends on your site, plans, and selections. A free Casita site walk turns the estimate into a real proposal for your property.
A complete ADU budget covers design and engineering, permits and fees, site work and utilities, foundation and framing, roofing and exterior, windows and doors, plumbing, electrical and HVAC, drywall and interior finishes, and the kitchen and bathrooms. Casita's estimate breaks each of these out so you can see where the money goes.
Ready for a number you can actually plan around?
A free site walk turns this estimate into real pricing for your property. No pressure, no obligation — just straight answers.