The cheapest ADU quote is rarely the cheapest ADU. In San Diego, two bids for the same unit can look tens of thousands of dollars apart simply because one includes permits, utilities and site work and the other does not. To compare quotes fairly, line them up item by item, confirm what each one excludes, and check the contract terms before you look at the total.
This guide walks through what a complete ADU bid should include, the red flags to watch for, and the questions that make every builder show their real price.
Why ADU quotes vary so much
An ADU is a full home built on an existing lot. That means design, engineering, permits, utilities and construction all have to come together. Builders price those pieces very differently.
Some quote a “build price” for the structure only. Others quote turnkey, from design to final inspection. Some use low allowances for finishes, which makes the quote look cheaper until you pick real cabinets and tile. Before you compare totals, make sure you are comparing the same scope. For a full breakdown of typical budgets, see our ADU cost in San Diego guide.
What every San Diego ADU bid should include
Use this checklist on every quote. If an item is missing, ask whether it is excluded or simply not written down.
| Bid item | What to look for | Why it matters |
|---|---|---|
| ADU type and size | Detached, attached, garage conversion or JADU, plus square footage | Each type has different costs and rules |
| Design and architecture | Floor plans, elevations, revisions included | Some bids charge design separately |
| Structural engineering | Foundation and framing calculations | Required for most new ADUs |
| Title 24 energy report | Energy compliance documents | Required for plan approval in California |
| Permits and plan check | Who pulls permits, and whether City fees are included or estimated | Fees can be significant and are often left out |
| Utility connections | Water, sewer, electrical and gas tie-ins, panel upgrade if needed | One of the most common surprise costs |
| Site work | Grading, demolition, trenching, access, retaining walls | Sloped or tight San Diego lots add cost |
| Foundation | Slab or raised, with soil conditions noted | Poor soil can change the price |
| Finish allowances | Dollar amounts for cabinets, counters, flooring, fixtures | Low allowances hide the real cost |
| Appliances | Listed by model or allowance | Often excluded |
| Solar | Whether panels are included | New detached ADUs generally need solar under California’s energy code |
| Timeline | Design, permit and build phases with dates | Shows whether the builder has a realistic plan |
| Warranty | Length and what it covers | Protects you after move-in |
Costs that are often left out of ADU quotes
These are the items that most often turn a “good” quote into an expensive project:
- City and agency fees. Plan check, permit and inspection fees, plus school fees, which apply to ADUs over 500 square feet.
- Impact fees. Under California law, ADUs under 750 square feet are exempt from impact fees. Larger units may pay fees in proportion to the main home.
- Utility upgrades. An older main panel, a long sewer run or a new water meter can each add thousands.
- Landscaping and hardscape. Paths, fencing and patios around the ADU are frequently excluded.
- Survey and soils report. Some lots need them before engineering can start.
For the current local rules behind many of these items, read our guides to San Diego ADU requirements and ADU regulations and recent updates.
How to compare ADU quotes side by side
- Get at least three written bids for the same plan or the same size and type of ADU.
- Put them in one spreadsheet, using the checklist above as rows.
- Mark every exclusion. Give each missing item a realistic estimate so all bids cover the same scope.
- Compare allowances. Raise any low allowance to a realistic figure for the finishes you actually want.
- Check the payment schedule. Payments should follow completed milestones, not dates.
- Compare timelines. A builder who promises permits in two weeks is either very experienced with the City or overpromising. Ask which.
- Only then compare the totals.
The bid that comes out lowest after this exercise is often not the one that looked lowest at the start.
Red flags in an ADU quote
Watch for these warning signs:
- A large deposit before work starts. California law limits the down payment on a home improvement contract, including an ADU, to $1,000 or 10% of the contract price, whichever is less. A builder asking for more is breaking the rule. See the CSLB guidance on down payments.
- Payments ahead of the work. Progress payments should not exceed the value of work completed or materials delivered.
- A one-page quote. A real ADU bid runs several pages and lists scope, exclusions and allowances.
- “Permits by owner.” This can shift legal responsibility for the work onto you.
- No license number. Every California contractor bid should show a license number. Check it on the CSLB license lookup.
- Pressure to sign today. A fair price will still be fair next week.
Questions to ask every ADU builder
- How many ADUs have you completed in the City or County of San Diego?
- Can I see two or three finished projects and speak to those homeowners?
- Is your quote fixed price, or are there items that could change?
- Who handles permits and plan check corrections?
- Who is my main point of contact during the build?
- Do you carry general liability and workers’ compensation insurance?
- What happens if the City asks for changes to the plans?
- How are change orders priced and approved? (California requires them in writing.)
These questions overlap with how you would vet any builder. Our guide on how to choose a general contractor in San Diego covers licensing, insurance and contract checks in more detail.
Design-build vs. separate designer and builder
You can hire an architect and a builder separately, or use a design-build firm that handles both. Separate hiring gives you more control over design but adds coordination, and the design can come back over budget. Design-build gives you one contract and one point of responsibility, with pricing checked against the design as it develops.
Whichever you choose, ask for the build price to be estimated early, before the plans are finished. If you are still deciding on a layout, browse our ADU design ideas for San Diego homes.
Get a clear, itemized ADU quote
NJ Design & Build is one of the licensed ADU builders in San Diego that provides itemized, design-to-final quotes. Every bid lists what is included, what is excluded and what the allowances are, so you can compare it fairly with any other quote.
Call us at (619) 966-7766 or request your ADU quote online.
Frequently asked questions
How many ADU quotes should I get in San Diego?
At least three. That gives you a fair view of the market and makes it easier to spot a bid that leaves out major costs.
Why is one ADU quote so much cheaper than the others?
Usually because it excludes items such as permits, utility connections, site work or appliances, or uses low finish allowances. Compare scope before price.
How much can an ADU contractor ask for upfront in California?
No more than $1,000 or 10% of the contract price, whichever is less. Later payments should match the work completed.
Are ADU permit fees included in contractor quotes?
Sometimes. Many quotes list City fees as an estimate or exclude them. Ask the builder to state this in writing.
Do I pay impact fees on an ADU in San Diego?
ADUs under 750 square feet are exempt from impact fees under state law. Larger ADUs may pay fees in proportion to the main home’s size.
