How Much Does a ADU Cost in San Diego? (2026 Data)

The short answer: adu cost San Diego depends on scope before it depends on finishes. A clean estimate should show labor, materials, permits, and contingency separately. If one line says “complete adu” with no quantities, you are looking at a dispute waiting to happen.

ADU Cost Breakdown in San Diego

Use the published total as the anchor. The percentages are a sanity check. Labor should not disappear into a lump sum, materials should have allowances, and contingency should be visible. Hidden contingency inside a contractor’s margin makes change orders harder to judge.

What Drives the Cost Up in San Diego Specifically?

San Diego adds pressure through seismic code, busy inspection calendars, tight staging, and premium finish labor. A bid can look cheap because it ignores the local friction. Ask how many inspections are assumed. Ask whether parking, debris, protection, and access are priced. Ask who pays when the inspector asks for a correction.

The usual cost drivers are utility trenching, fire access, school fees, separate meters. The expensive version of this project is rarely one upgrade. It is usually three small misses stacked together: unclear scope, low allowances, and no plan for surprises.

5 Hidden Costs Most Contractors Don’t Tell You About

1. Demo exposes prior work. Old wiring, bad framing, rot, and unpermitted changes can turn a clean scope into a correction job.
2. Allowances are often too low. A $3,000 allowance can become $7,000 once the owner picks real fixtures.
3. Protection and cleanup cost money. Dust barriers, floor protection, haul-off, and daily cleanup should be priced.
4. Change-order overhead is real. A $1,200 field change can carry supervision, procurement, and schedule costs.
5. Delay costs compound. One late inspection can affect subs, temporary housing, storage, or missed rental income.

Is $150-$350 a Realistic ADU Cost in San Diego?

Yes, as a published planning range. It is not a contract price. Compare it against your quantity takeoff, finish schedule, and site conditions before you accept a bid.

Why Are Contractor Bids So Different?

One contractor may include permits, protection, debris, management, and contingency. Another may leave those as owner costs or change orders. Normalize the scope before comparing totals.

What Should Be Included in the Estimate?

Look for demolition, labor, materials, permits, subcontractors, supervision, cleanup, warranty, payment schedule, and exclusions. Missing exclusions are a red flag.

How Much Contingency Should I Carry?

Carry 10% to 15% for most residential jobs. Use the higher end when the home is old, access is tight, or drawings are thin.

Can CostCheckGPT Review My ADU Estimate?

Yes. Paste the bid into CostCheckGPT and ask it to flag missing line items, soft allowances, vague exclusions, and cost ranges that look light for San Diego.

When Should I Get a Second Bid?

Get a second bid when one proposal is more than 15% away from the others, when line items are vague, or when the contractor asks for a large deposit before scope is clear.

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