Detached ADU
A detached ADU: a small home behind yours
A detached unit stands on its own foundation, with its own door, kitchen, bath and heating and cooling. Most are one bedroom near 600 sq ft; the larger two-bedroom runs up to 1,200 sq ft.
Because nothing existing has to be reworked, the schedule is the easiest to plan. The cost depends mostly on the ground it stands on and how far the utilities have to travel.
One or two bedrooms, up to 1,200 sq ft
22 to 36 weeks to build
Priced for your lot, in writing after a site visit
What moves the price
Six things that move a detached ADU price
We name each one on your quote. None is a surprise if the lot check has found it first.
Distance to utilities
Trenching for sewer, water and power adds cost for each foot it runs.
Slope and access
A sloped yard needs a deeper foundation. A narrow side yard may mean hauling by hand.
Soil
Soft or expansive soil can call for a thicker slab or deeper footings.
Size and shape
A simple rectangle costs less per square foot than a unit with many corners.
Finishes
Tile, cabinets and windows are the largest swing after the structure.
City requirements
A fire sprinkler, a larger electric panel or a sewer upgrade are added only if your city asks.
The build weeks
What the weeks hold
A one-bedroom, 22 to 28 weeks.
- Weeks 1 to 5
Step 1: Site and foundation
Clear, mark, trench for utilities, pour the foundation and wait for the inspection.
- Weeks 6 to 12
Step 2: Frame, roof and windows
The walls go up in days; roofing, windows and the weather barrier follow.
- Weeks 12 to 18
Step 3: Rough-in and inspections
Plumbing, wiring and the mini-split are run before the walls close. The city inspects each.
- Weeks 18 to 28
Step 4: Finishes and final
Drywall, paint, cabinets, tile, fixtures, then final inspection and the utility meter.
Rules to know
Setbacks, height and rental
Under California law, a city may not require more than a 4-foot setback from the side and rear lot lines for most new detached ADUs. Height limits and size caps vary by city and by lot, and we read them from your city's code at the lot check.
Most ADUs can be rented, usually for 30 days or longer. In most cases an ADU cannot be sold apart from the main house.
If your house was built before 1978, ask us about lead paint before you sign. Work that disturbs painted surfaces needs specific lead-dust practices by a certified firm, and your quote says who holds the certification.
Questions
Asked about this type
Can I build an ADU on my lot?
Most single-family lots in San Diego County can fit at least one. Size, setbacks, utility lines and easements decide what kind. A lot check answers it for your address before you pay for drawings.
What about water, sewer and power?
The unit needs a way to connect. Sometimes it ties into the house lines, sometimes it needs a new meter or a larger panel. We find out which at the lot check and list the cost as an allowance.
Can I rent it out?
Usually yes, for stays of 30 days or longer. Rules on owner occupancy and on selling the unit apart from the house differ by unit type and city. A junior ADU, for example, needs the owner to live on the property. We write down the rules for your address.
How long does it take?
Design takes about two months, the city review varies, and the build runs 10 to 36 weeks depending on the type. The weeks on the cards are build time only.
My house was built before 1978. Does that change anything?
It can. Homes built before 1978 may have lead paint. If work disturbs more than 6 square feet of painted surface inside or 20 outside, or touches windows or demolition, federal rules require specific lead-dust work practices by a certified firm. Tell us the year; we say before you sign whether the rule applies and who holds the certification.
Does a detached unit fit your yard?
Send the address. We read the parcel and call with an answer.