What our ADUs have cost
These are the totals we have historically seen on our own ADU jobs in Santa Cruz County.
| Type of ADU | Historically, around |
|---|---|
| Garage conversion | $320,000 |
| Studio | $400,000 |
| One-bedroom | $525,000 |
| Two-bedroom | $650,000 |
Your lot is what turns a typical number into your number. The rest of this guide covers the parts of a budget that the City and County publish themselves.
Size: the 750 square foot line
Fees drop sharply below 750 square feet. In the unincorporated County, ADUs under 750 square feet are exempt from impact fees and most building permit review fees. The County gives its own example: fees for a new 750 square foot ADU are about $25,000, against about $5,000 for a 640 square foot one.
In the City of Santa Cruz, ADUs under 750 square feet also fall below the threshold for school impact fees, which the City puts at around $3.15 a square foot.
Conversion or new construction
Both the City and the County say a new, detached backyard cottage is the most expensive kind of ADU, in construction and in fees. Converting space you already have, such as a garage or part of the house, can cost substantially less to build and permit.
In the County, conversion ADUs get reduced building permit fees, and the County waives its sewer and water connection fees for conversion ADUs and junior ADUs. A conversion still needs a full bathroom, a full kitchen, its own entrance and its own heat source.
Garage, backyard or part of the house? The quiz asks what you have to work with and tells you what likely fits.
Take the quizWater and sewer connections
This is where two lots with the same cottage can end up far apart.
- City of Santa Cruz. The City says a detached new-construction ADU will almost always need new water and sewer connections, with the fees that come with them. Conversions and attached ADUs don't need separate connections, but can outgrow the existing water meter, and upsizing it can mean opening the street.
- County sewer. If your lot is on a County sewer system, new-construction ADUs pay connection fees, conversion ADUs don't, and every ADU adds an annual sewer assessment on the property tax bill.
- Soquel Creek Water District. If your water bill comes from this district, every new ADU needs its own district water service, and the district publishes its ADU water service charges on its development services page.
Septic
If your house is on septic, the County asks you to talk to Environmental Health early, because a parcel on septic may need a septic upgrade before an ADU can be added. The County's own advice for keeping the cost down is to place the ADU close to the system and on the uphill side.
The lot itself
- Slope. The City notes that a unit on a slope needs more careful engineering and can cost more to build.
- Alleys and driveways. If the ADU sits on an unpaved alley, the City says you could be responsible for paving your stretch of it. A longer driveway, which isn't required, adds paving and drainage.
- Parking. In the County, a new-construction ADU needs one parking space, with exceptions near transit, in historic districts and near car share, except in certain coastal areas where the space is always required.
- Solar. A detached ADU has to meet the state's solar panel requirement, so the County reminds owners to put the panels in the budget.
How we price a project
After a call about your address, Warren Swanepoel, the owner of WS Builders, walks the lot. You get a fixed price in writing before any work starts, and the finish date is written into your contract. Design, permits and construction are all done by our team.
Questions homeowners ask
Is a garage conversion cheaper than a new backyard cottage?
Usually. The City and County both say a new detached unit is the most expensive kind of ADU. Historically, our garage conversions have come in around $320,000, against around $400,000 for a new studio.
Does building smaller really save money on fees?
Yes. In the County, ADUs under 750 square feet skip impact fees and most building permit review fees. The County's own example puts a 750 square foot unit at about $25,000 in fees and a 640 square foot unit at about $5,000.
Is there a way to estimate County fees myself?
Yes. The County publishes an ADU Fee, Cost and Cash Flow Estimator on its ADU pages.
The quickest way to know what your own lot allows: the 60-second quiz, then a free 20-minute call with Josh if you want one.
Take the quizSources
- Plan Your Financing (fees, conversions, septic, sewer, solar), County of Santa Cruz
- ADU Basic Requirements (fee waivers, parking, septic), County of Santa Cruz
- ADU Fee, Cost and Cash Flow Estimator, County of Santa Cruz
- Accessory Dwelling Units (school fees, water and sewer, site planning), City of Santa Cruz
- Development Services (ADU water service), Soquel Creek Water District
- Typical totals: WS Builders' own ADU projects in Santa Cruz County.
Rules change. We checked every source on October 27, 2026. Call the City or County planning counter before you design.