ADU construction · San Jose & the Bay Area
ADU Construction in San Jose, CA
An accessory dwelling unit (ADU) is a second, complete home on your property. Whether it is built in the backyard, attached to the house or converted from a garage, the work is the same discipline: the right site, the right permit and a unit built to code.
- CSLB Lic. #1003436
- Free estimates
- (650) 749-7436
What is an ADU, in plain terms?
Industry Resources & Standards:
An ADU is a self-contained home on the same lot as a single-family house, with its own entrance, kitchen, bathroom and sleeping area. California law encourages them to ease the housing shortage, and it limits what cities can require.
ADUs are used for family members, rental income, guests, home offices and aging in place. The four formats below cover almost every project.
Four kinds of ADU
| Type | What it is | State size guide | Learn more |
|---|---|---|---|
| Detached ADU | A new, separate building in the yard (a guest house) | Up to 1,200 sq ft where a city has no compliant ordinance; cities must allow at least 800 sq ft | Guest houses |
| Attached ADU | A new addition built onto the house, with its own entrance | Up to 50% of the main home’s floor area, and at least 800 sq ft | Room additions |
| Converted ADU | Existing space such as a garage turned into a unit | Within the existing structure; up to 150 sq ft can be added for access | Garage conversions |
| Junior ADU (JADU) | A small unit built within the walls of the existing house | No more than 500 sq ft, with an efficiency kitchen | Garage conversions |
Several types can sometimes be combined on one lot. What your lot allows depends on its size, the existing buildings and your city’s standards.
The state rules that help homeowners
These points come from the California Department of Housing and Community Development (HCD) ADU Handbook. State law was renumbered in 2024, so the section numbers below are the current ones.
| Topic | What the state says | Gov. Code |
|---|---|---|
| Review time | A completed application must be approved or denied within 60 days when the lot has an existing home | § 66317(a)(3) |
| Replacement parking | Not required when a garage is converted to an ADU | § 66314(d)(11) |
| Parking for the ADU | A city cannot require more than one space per unit or per bedroom, whichever is less | § 66314(d)(10)(A) |
| Setbacks | Four-foot side and rear setbacks are the standard for an ADU of at least 800 sq ft; none for a conversion of existing space | § 66321(b)(3), § 66314(d)(7) |
| Owner occupancy | A city cannot require the owner to live on the property | § 66315 |
| Impact fees | None for an ADU of 750 sq ft of interior living space or less | § 66311.5(c) |
| Fire sprinklers | Building an ADU cannot trigger sprinklers in the existing home | § 66314(d)(12) |
Source: California HCD, Accessory Dwelling Units and its ADU Handbook. Cities can adopt their own, less restrictive standards, and the rules change. Confirm the current requirements for your address with the City of San Jose or your city’s permit office before you commit to a plan.
Which type fits your lot?
You have a garage you rarely use for cars: a conversion is usually the shortest path, because the slab, walls and roof already exist.
You have a deep or wide yard: a detached ADU gives the most privacy and design freedom, but needs a new foundation and utility runs.
You want the unit connected to the house: an attached ADU shares a wall and some utilities with the main home.
You want a small suite for a relative or renter: a junior ADU turns an existing bedroom area into a separate unit inside the house.
Where to start: a site visit. We measure the lot and the garage, check the utilities and tell you which of these your property can support.
How an ADU project typically runs
Feasibility
Check the lot, setbacks, utilities and what the city allows, and agree the type, size and layout.
Design and permit
Prepare the drawings and energy documents, submit the application and respond to plan-check comments.
Site work and foundation
Grade the site, set forms and rebar, and pour and inspect the slab or footings.
Framing and shell
Frame the walls and roof, then add the wrap, windows, doors and siding.
Utilities and interior
Run plumbing, electrical and mechanical, pass inspections, then insulate and finish.
Final inspection
The city’s final inspection before the unit can be occupied.
ADU work in San Jose
ADU questions
Do I need a permit for an ADU?
Yes. Every ADU needs a building permit, with inspections for the structure, electrical, plumbing and energy work. We prepare the plans and handle the application.
How long does the permit take?
For an ADU on a lot with an existing home, state law requires the city to approve or deny a completed application within 60 days (Gov. Code § 66317(a)(3)). The full timeline also depends on plan-check comments and the build.
Can I rent out my ADU?
Generally yes, and California does not let a city require the owner to live on the property (Gov. Code § 66315). Rental terms and other rules are set separately, so check your city.
Do I have to provide parking?
State law caps ADU parking at one space per unit or per bedroom, whichever is less (Gov. Code § 66314(d)(10)(A)), and a city cannot require replacement of garage parking when a garage is converted (§ 66314(d)(11)). Local exceptions can apply.
What is the difference between an ADU and a JADU?
An ADU is a complete, independent unit. A junior ADU is limited to 500 square feet and is built within the walls of the existing house, with an efficiency kitchen.
Can I build more than one ADU?
State law lets some formats be combined on a single-family lot. The combination your lot allows depends on its size and your city’s standards, so we confirm it during the feasibility visit.
How much does an ADU cost?
It depends on the type, size, foundation, utility runs and finishes. We give a written estimate after seeing the property. Call (650) 749-7436 to schedule one.
Related services
What Our Clients Say
Join hundreds of happy Bay Area homeowners who trusted Quartz Construction & Remodeling for their projects.
Professional Resources & Regulations
- California Contractors State License Board (CSLB) — Verify contractor licenses
- City of San Jose Building Permits — Permit requirements & inspections
- ENERGY STAR — Energy-efficient materials & standards
What our clients say on Google
Verified reviews from our Google Business Profile. See all reviews on Google.
Get Your Free Estimate
Licensed • CSLB#1003436 • Serving San Jose & Bay Area
Or call us directly: (650) 749-7436
Quartz is a construction and remodeling company serving San Jose and the nearby areas. Our firm offers a wide range of services, including full-home renovations, kitchen remodeling, bathroom renovations, window replacement, deck building and repair, patio construction, and more.
Location
Address: 1777 Hamilton Avenue #1080, San Jose, 95125 California, USA.
Mon-Sat: 08:00 – 19:00
Follow us
© 2025 Quartz Construction and Remodeling, San Jose, California.