The honest answer is a range, not a number — and anyone who gives you an exact price without walking your lot is guessing. Below are the ranges San Diego ADU builders themselves publish, what moves a project up or down inside them, the permit and utility fees people forget to budget, and a simple educational estimator to play with.
These are published ranges from San Diego ADU builder guides (2026), shown so you can plan. They are not a quote, an estimate, or an offer for your project — only a licensed builder who has looked at your property can price your ADU.
| ADU type | Published range | Guide |
|---|---|---|
| Junior ADU (JADU), inside the existing home | $50,000 – $100,000 | Can I build one? — eligibility check |
| Garage conversion | $100,000 – $210,000 | Garage conversion cost guide |
| Detached new build | $300,000 – $450,000+ (about $375–$600 per sq ft) | Detached ADU cost guide |
Why the ranges are wide: size, site conditions, how far the new unit sits from existing water/sewer/electric lines, finish level, and your city's fees all move the total. Two ADUs of the same size on different lots can honestly differ by six figures.
Usually the cheapest path to a legal unit — the published $100k–$210k range, what the money actually goes to, and when a conversion is not cheap after all.
Read the guide →The published $375–$600 per sq ft, the size math at 600–1,200 sq ft, and the cost stack behind a backyard build.
Read the guide →Eight quick questions — city, ownership, garage, HOA, septic — and a plain-language likely / maybe / talk-to-the-city result.
Read the guide →Pick a type, a size, and a finish level. The estimator applies the published per-square-foot bands behind the ranges above. It is a planning toy, not a pricing tool.
Educational estimate range only — not a quote, not an offer, and not a price for your property. It does not include financing costs, and permit, school, and utility charges vary by city and property (see the fee notes below). Only a licensed builder who has seen your property can price your project.
Download this guide as a printable PDF
The PDF is the same ranges, drivers, and fee notes on this page in a clean printable file — the version homeowners share in neighborhood groups and with family.
San Diego ADU Match is a matching service, not a contractor. We never quote or estimate a price for your property, and we do not give feasibility or legal opinions — those calls belong to licensed builders and your city. Guides on this site are general information, not advice about your property.
Construction is only part of the check you write. These are general notes to budget around, not figures for your property — amounts are set by your city and utility providers and depend on the project.
A licensed builder looks at your lot, your city's rules, and your budget band, and tells you plainly whether the project pencils. This is the step a match request starts.
Custom plans or a preapproved plan set, then city plan check and a building permit. Timelines vary by city — Oceanside, for example, publishes a 60-day permit-review clock.
Construction in stages with city inspections along the way, ending in a final sign-off. You contract and pay the builder directly — a matching service is never in the middle of the money.
That feasibility conversation — your lot, your city's current rules, your utilities, your budget — is the real answer to every cost and rules question. It is exactly what a match request starts: one licensed local builder, matched to your project, and nobody else.
The intake form lives on our main page — that page states whether intake is currently open.