Thinking about adding more living space without moving? You’re not alone. In San José, many families are building ADUs — small homes on the same lot as the main house — to help aging parents, grown kids, or to earn extra rent.
With high housing prices and jammed schedules, it really does help to have things be simple and clear. This guide breaks down ADU construction San Jose in plain English, with real examples and tips you can use today.
Let’s walk through it together. 🏡
What’s an ADU, and Why San José?
An ADU (Accessory Dwelling Unit) is a small, full home on your property. Think: a studio, one-bed, or two-bed with a kitchen and bathroom. In San José and across the ADU construction Bay Area scene, ADUs are popular because they:
Add flexible space for family or rental income
Cost less than buying a new home
Can boost property value
Common ADU types:
Detached ADU: a small house in the backyard
Attached ADU: added onto your main home
Garage conversion: turns an existing garage into a home
Junior ADU (JADU): up to 500 sq. ft. inside the main home; usually shares a bathroom
If you only need extra space (not a separate unit), room additions San Jose could be the better fit. We’ll compare both options below.
Why San José Is a Great Place to Build
San José follows California’s ADU-friendly laws and has a helpful local program. Here’s what most homeowners care about:
Faster approvals: State law says the city must review your ADU permit within 60 days.
Setbacks: Many detached ADUs can sit as close as 4 ft from side and rear property lines.
Size: An ADU up to 800 sq. ft. is allowed on most lots that meet basic rules. Larger (up to 1,200 sq. ft.) may be possible depending on zoning and lot size.
Parking: Often not required if you’re near public transit or converting an existing structure (like a garage).
Fees: Impact fees are waived for ADUs under 750 sq. ft. (Other fees, like school fees, may still apply.)
No public hearing: ADU permits are “ministerial,” so you don’t need a big neighborhood vote.
Tip: San José has pre-approved plan options and an ADU help page. Using those can cut time and cost.
ADU vs. Room Addition: Which One Fits?
Choose an ADU if you want:
A private, rentable unit
A full second kitchen/bath
Space for multigenerational living with privacy
Choose a room addition if you want:
More space for your family only
A faster, cheaper way to add a bedroom or family room
To avoid adding a second kitchen
Many families price both before deciding. A quick chat with a designer can make the choice clear.
The Step-by-Step ADU Building Process
Here’s the simple path most San José homeowners follow.
1) Set Goals and Budget
Who will live here, and for how long?
Target size (studio, 1-bed, or 2-bed)?
Budget range (with a 10–15% contingency)
All-electric or gas? (All-electric is common and often cheaper to set up.)
Money tip: Decide early if this is for family, rent, or both. It affects layout, finishes, and return on investment.
2) Check Your Site
Measure your lot and note where utilities enter (water, sewer, electric).
Find any big trees, slopes, or drainage issues.
Snap photos of the backyard and property lines.
City rules to confirm:
Minimum setbacks (often 4 ft side/rear)
Maximum ADU size for your lot
Height limits (cities must allow at least 16 ft; some sites allow taller)
Parking exemptions (many areas near transit don’t need extra parking)
Tip: A short call with a local designer or the city’s ADU desk can save weeks.
3) Pick Your ADU Type
Garage conversion: Often the cheapest and fastest if the structure is sound.
Detached new build: Most flexible and private; great for rentals.
Attached: Good if you want the ADU close to the main home.
JADU: Budget-friendly, up to 500 sq. ft. inside the main house. Note: JADUs usually require owner-occupancy.
4) Design (2–8 weeks)
Choose pre-approved plans for speed and savings, or go custom for a perfect fit.
Keep the shape simple (a rectangle saves money).
Line up the kitchen and bath near existing plumbing if possible.
Plan for energy code (Title 24). Heat-pump water heaters and mini-splits are common and efficient.
Think accessibility: no steps, wider doors, curbless shower — future-you will thank you.
5) Permitting (about 4–10 weeks)
You’ll submit:
Site plan showing setbacks, parking, and utilities
Floor plan and elevations
Basic structural details
Energy and green building forms (Title 24 and CALGreen)
For garage conversions: existing and proposed plans
What to expect:
The city checks your plans (usually within 60 days)
You fix any comments
You pay fees (impact fees waived under 750 sq. ft.; school fees often apply)
No public hearing needed
6) Bids and Financing
Common funding options:
HELOC (home equity line)
Cash-out refinance
ADU construction loan
Savings or family help
Tip: Ask builders for “apples to apples” bids with the same scope. Include site work, utility upgrades, and finishes.
7) Pre-Construction Setup
Finalize the contract, schedule, and allowances
Order long-lead items (windows, electrical panel, heat pump)
Talk to neighbors about timing and access (keeps things friendly)
8) Build (about 3–9 months)
Typical order:
Site prep and trenching for utilities
Foundation
Framing and roof
Rough plumbing, electrical, HVAC
Insulation and drywall
Cabinets, tile, flooring, paint
Final fixtures and appliances
City inspections, then Certificate of Occupancy
Rough timelines:
Garage conversion: 3–6 months
Detached 1-bed (400–800 sq. ft.): 6–9 months
Prefab/modular: structure can arrive faster, but site and utility work still take time
9) Move-In and Enjoy
Set up mail, address numbers, and trash service
Decide on renting (most areas require 30+ day rentals; check local rules)
Keep a simple maintenance list (filters, gutters, caulking)
What Does an ADU Cost in San José?
Ballpark ranges (every site is different):
Garage conversion: – 140k–220k+
Detached 1-bed (400–800 sq. ft.): – 220k–380k+
Larger custom ADUs: – 350k–500k+
What drives cost:
Utility upgrades (200-amp electrical panels are common)
Sewer line condition and distance
Slopes, retaining walls, and drainage
Fancy finishes or complex rooflines
Separate utility meters (optional)
Ways to save:
Stay at or under 750 sq. ft. to avoid impact fees
Use pre-approved plans and simple shapes
Choose standard-size windows and doors
Go all-electric (often cheaper to install)
Keep plumbing close together (kitchen/bath back-to-back)
Pick durable, mid-grade finishes (vinyl plank floors, quartz tops)
Real-Life Stories
Maria in Willow Glen turned her old detached garage into a bright 380 sq. ft. studio for her mom. The surprise? The sewer line needed repair. Her builder caught it early and adjusted the plan. Total cost ended near $165k, and the whole process took about six months. When her mom moved out, Maria rented it to a traveling nurse for steady income.
Rahul and Priya in Berryessa built a 2-bed, 800 sq. ft. detached ADU using a pre-approved plan. Permit review took seven weeks, and construction finished in eight months. They spent about $295k. Their parents live there now, and childcare just got a lot easier.
Quick Rules Check (Helpful, Not Legal Advice)
Size: 800 sq. ft. allowed on most lots; up to 1,200 sq. ft. may be possible depending on zoning
Setbacks: Often 4 ft side/rear for detached ADUs
Height: At least 16 ft allowed by state law; some sites allow more (check with the city)
Parking: Often not required near transit or for conversions
Owner-occupancy: Not required for most ADUs; usually required for JADUs
Fire sprinklers: Usually not required if the main house doesn’t have them (confirm with the fire department)
Rentals: Long-term rentals are generally allowed; short-term limits vary
Always confirm current rules with the City of San José before you start. Codes change.
ADU Construction Bay Area vs. San José: Any Differences?
Across the Bay Area, rules are similar thanks to state law. Still, each city can add small changes (height where transit is nearby, lot coverage, local fees, or historic rules). If you own property in different cities, check each city’s ADU page. Pre-approved plans and permit timelines can vary.
Simple Starter Checklist
Walk your yard and sketch possible ADU spots
Decide your size target (e.g., 500–750 sq. ft. to save on fees)
Call your city’s ADU help desk or a local ADU designer
Compare pre-approved plans vs. custom
Get at least two builder bids with the same scope
Pick financing, set a 10–15% contingency
Talk with neighbors early
Choose durable, simple finishes to stay on budget
When a Room Addition Makes More Sense
Room additions San Jose can be faster and cheaper if you just need:
One more bedroom or a bigger family room
No second kitchen
A lower-cost way to expand the main house
If you want privacy or rental income, an ADU wins. If you only need space, a room addition can be the budget hero.
FAQs
How long will it take?
From first call to move-in, plan for 6–12 months depending on type and size.Can I rent it out?
Long-term rentals are usually fine, but check San José’s current rules on minimum stay lengths.Do I need parking?
Often no, especially near transit or for garage conversions.Will I need a new electric panel?
Many homes upgrade to 200 amps for an ADU. Your electrician can confirm after a load calc.Is prefab faster?
The structure may be quicker, but you still need permits, foundation, and utility work. Total time can be similar, but prefab can reduce on-site disruption.
Ready to Start? Here’s Your Next Step
Take a 20-minute yard walk and mark two possible ADU spots.
Set a “not-to-exceed” budget range and a wish list.
Email a local ADU designer or builder with photos and your goals.
Small steps today lead to keys in hand tomorrow. If you’re weighing ADU construction San Jose or comparing with room additions San Jose, this is the moment to explore. Your future self — and maybe your family — will thank you.
