How Much Does an ADU Cost?
It depends on your land, your city, and what you want. Construction for some ADU projects starts around $300 per square foot.
Here is where the money goes, and how to get a free estimate for your lot.
A rough idea of the cost
Construction for some ADU projects starts around $300 per square foot. That is for construction only, so plans and permits are extra. Your price can change based on the scope of the project and the finishes you pick.
Scope means how much work your project needs. Finishes are the things you see every day, like floors, counters, and tile.
No two lots are the same, so we need to see your lot and check with your city first. Your estimate is free. It is a ballpark number, so it can change as we work out the details.
What you pay for
An ADU is more than walls and a roof. These are the parts of the total cost. The building itself is the biggest part.
Site check
We look at your lot, your utilities, and your city's rules to see what can be built.
Surveys and reports
A survey maps your land. Some cities also want a soil report, which tests the ground.
Plans and engineering
These are the drawings for the city and the crew. Engineering makes sure the building is strong and safe.
Permit help
We fill out the forms, turn them in, and answer the city's questions.
City fees
Cities charge fees for permits. Some also charge for schools and sewer hookups.
Work on your lot
We get the ground ready, dig trenches, and hook up water, sewer, and power.
The building
This covers the foundation, frame, roof, walls, kitchen, bathroom, and basic finishes.
Upgrades
This is your choice. Think nicer counters, tile, or appliances.
Extra lot work
Some lots need more, like a retaining wall, which holds back a slope. It can also mean tearing out old concrete.
What moves your price the most
- Size. A bigger ADU costs more in total.
- Slope. A flat lot costs less than a hill.
- Utilities. Long runs to the sewer or power line cost more. You may also need a new power meter.
- Access. Tight side yards make it hard to bring in machines and supplies.
- Your city. Fees and required reports are not the same in each city.
- Finishes. Your counters, floors, and appliances change the price.
- Your HOA. It may want the ADU to match your home.
Why small ADUs cost more per foot
Small ADUs often cost more per square foot than big ones. Here is why.
Every ADU needs a kitchen and a bathroom. Those are the most costly rooms to build. Plans, permits, and hookups are needed at any size too.
So a small ADU spreads those costs over fewer feet. The total is still lower, but the price per foot goes up.
State rules that can save you money
- 750 square feet or less
- No impact fees. An impact fee is money a city charges for new building. Your ADU is exempt at this size.
- Over 750 square feet
- Impact fees can apply, but they must be fair for the size. Say your home is 2,000 square feet and your ADU is 1,000. The fee could be 50% of what a new house would pay.
- 500 square feet or less
- No school fees. Above this size, a school district can choose to charge them.
Source: California ADU Handbook, March 2026. Other city fees can still apply.
Ways to spend less
- Convert a garage if you have one. There is less to build.
- Stay at 750 square feet or less to skip impact fees.
- Pick a simple shape. Corners and extra roof lines add cost.
- Build close to your sewer and power lines.
- Use a flat spot on your lot if you can.
- Start with standard finishes and upgrade only what you care about.
How we handle your price
We talk about money from the very first call. You should know your budget before you pay for plans.
When we build, you get a fixed price with no hidden change orders. A change order is a bill for extra work. You will know the number before work starts.
How people pay for an ADU
We don't make loans. We can point you to third-party lenders, which are separate companies. Each lender sets its own rates and terms, and decides who gets a loan. These are common ways to pay:
Savings
You pay with cash you have. There is no loan and no interest.
Home equity line
Equity is the part of your home you own. You borrow against it as you need the money.
Cash-out refinance
You get a new, bigger home loan and take the extra in cash. This changes your mortgage rate.
Construction loan
A loan made for building. The bank pays out in steps as the work gets done.
Some cities offer help, like lower fees. When the state's March 2026 handbook came out, its ADU grant money had run out. Ask your city what is open now.
Questions people ask
Why do online prices look so low?
Many prices only count the building. They leave out plans, permits, and the work on your lot. Always ask what the number covers.
Is a garage conversion cheaper?
Most of the time, yes. The walls and roof are already there. You may still need new floors, power, and plumbing.
Do I pay for an estimate?
No. Your first call, home visit, and estimate are all free.
Can I change things after we start?
Yes. Tell us what you want to change, and we will show you the cost before we do it.
Is an ADU worth the money?
It depends on your goals. Rent money, family needs, and home value all count. We can help you run the numbers for your home.
Get a free estimate for your lot
Send us your address. We will come out for a free consultation. Then you get a free estimate.