What drives the cost
No two lots price the same. Here is what moves the number, and the list of what a complete quote has to include so you can compare bids line by line.
Five things that matter most
The lot moves the number more than the floor plan does.
A junior ADU inside the house is the smallest job; a second story over a garage is the biggest. Small buildings cost more per square foot, because a kitchen, a bath, a roof and a permit are spread over fewer feet.
How far the sewer, water and power have to travel, and whether the panel or the sewer line needs an upgrade.
A flat lot with a wide side yard is simple. Hillsides, tight access and retaining walls add work.
Plan-check and permit fees, school fees, fire sprinklers and hillside or fire-zone rules differ from city to city.
Cabinets, flooring, windows and fixtures. Every quote should name the allowance for each, in writing.
What a complete quote includes
A low bid is often missing several of these. Ask every builder to fill in each line, then compare complete quote to complete quote.
- Architectural design and construction drawings
- Structural engineering
- Title 24 energy report
- Survey
- Permit and plan-check fees
- School and impact fees
- Utility connections and meters
- Trenching and sewer work
- Site work
- Fire sprinklers, if your city requires them
- Finishes allowance, in writing
- Final clean
- Warranty
Where the money can come out
State law bars impact fees on ADUs under 750 sq ft, and everything else gets smaller too.
Adapting a plan that's already drawn takes less design time than a custom one.
Placing the ADU near the existing lines shortens the trench and the sewer run.
A small unit rarely needs as many heating and cooling zones as a house.
Cost questions
Can you give me a price now?
Not a responsible one before we've seen the lot. The free Lot Check tells you what fits; after design you get a written quote with every line filled in.
How much do I pay up front?
California caps a home-improvement down payment at $1,000 or 10% of the contract, whichever is less, and progress payments can't run ahead of the work. Be careful with anyone asking for more.
Do you help with financing?
We explain the options (HELOC, cash-out refinance, construction and renovation loans) and introduce licensed lenders. We don't arrange loans ourselves.
What would your lot need?
Send the address. We'll tell you what fits and the best next step. Free.