ADU 101
Everything you need to know before you build.
What an ADU is, what California law guarantees you, what it costs, and what it earns — the whole picture, in plain language, before you spend a dollar.
The basics
What is an ADU?
An accessory dwelling unit is a complete, self-contained home on the same lot as your house — its own entrance, kitchen, bathroom, and address. It can be a new backyard cottage, an addition to your home, or a converted garage.
To ease the housing shortage, California passed a series of state laws that legalized ADUs on virtually every residential lot and stripped away the local rules that used to block them — minimum lot sizes, owner-occupancy requirements, discretionary hearings. The state already said yes; your city works out the details.
The result: a backyard home that earns rental income, adds real square footage and equity, or houses the people you love — on land you already own.
The four types
Four ways to add a home.
Every lot is different. These are the four ADU types California law recognizes — and we build all of them.
Detached ADU
A stand-alone backyard home with its own entrance, kitchen, and real privacy — the highest square footage, rent, and resale value.
Up to 1,200 sq ftAttached / Bump-out
An addition built onto your existing home — ideal for tighter lots and lower budgets, matched to your house.
Seamless matchGarage conversion
Turn an underused garage into a fully permitted rental in the fastest timeframe — the structure already exists.
Fastest paybackJunior ADU
A compact unit carved from existing space — the lowest-cost path to rental income, skipping foundation and shell work.
Up to 500 sq ftCalifornia law
The state already said yes.
Six things California law guarantees every homeowner — no matter which city you live in.
Allowed on nearly every lot
ADUs are legal in every residential zone in California — with no minimum lot size. If you own a home, you can almost certainly build one.
Guaranteed square footage
Every city must approve at least 850 sq ft (studio / 1-bed) or 1,000 sq ft (2-bed+). Many allow detached ADUs up to 1,200 sq ft.
4-foot setbacks
Your ADU can sit just 4 feet from side and rear property lines, up to 16–18 feet tall — most backyards qualify.
Your garage counts
Legally built garages and accessory structures can be converted — or demolished and rebuilt as an ADU in the same footprint.
No one can veto it
HOAs can't prohibit an ADU, neighbors' sign-off isn't required, and you don't have to live on the property to rent it out (30-day+ rentals).
Usually no extra parking
Conversions need no new parking, and new ADUs near transit are exempt too. When one space is required, a tandem driveway spot counts.
Current as of 2026 state ADU law. Every city adds its own details — we confirm exactly what your lot allows, free, before you commit to anything.
What it costs
Plan around $450–$550 per square foot, all-in.
That range covers everything — design, engineering, permits, construction, and standard finishes. A 600 sq ft one-bedroom typically lands around $280,000–$300,000; a 400 sq ft studio in the low $200,000s — and larger plans bring the per-foot cost down. Here’s what moves the number.
Site work & utilities
The distance from your main panel and sewer line to the ADU, slope, and access for equipment set the foundation of the budget. Site work and utility runs cost roughly the same at any unit size — which is why cost per square foot drops as you grow.
Size & layout
Bedrooms — not raw square feet — drive rental income, and kitchens and baths are the most expensive rooms per foot. A well-planned 600 sq ft one-bedroom often out-earns a larger studio.
Finish tier
We build in three finish tiers — Standard, Premium, and Luxury — across siding, flooring, cabinets, counters, and fixtures. Standard is included in the base price; upgrades are priced line by line, so you choose where the dollars go.
Build under 750 sq ft and state law exempts you from city impact fees entirely — often a five-figure saving that makes compact units remarkably efficient.
What it earns
Income now. Equity forever.
An ADU is the rare investment you can live next to — it pays you monthly and adds lasting value to the property underneath it.
Rental income
$1,700–$2,000 / month
Southern California ADUs rent for roughly $2.90–$3.35 per sq ft across the county. A 600 sq ft one-bedroom brings in about $1,700–$2,000 every month, year after year — and bedrooms, not square feet, drive the rent.
Property value
Real square footage, real equity
A permitted, new-construction ADU adds appraisable living space to your property — equity you keep whether you rent the unit, house family, or eventually sell. Rental use can bring tax advantages too, and only the ADU’s added value is assessed — never your existing home.
Common questions
Asked at every consultation.
Straight answers to the questions homeowners ask us most — and anything we haven’t covered, we’ll answer on a free call.
Do I need to live on the property to rent out my ADU?
No. California law removed owner-occupancy requirements for standard ADUs — you can rent out the ADU (or the main house) without living on-site, as long as rentals are 30 days or longer. Short-term rentals under 30 days follow separate local rules that vary by city.
Can my HOA block my ADU?
No. State law prohibits HOAs from banning ADUs on single-family lots. An HOA can apply reasonable design guidelines — paint colors, materials — but it cannot prevent you from building, and your neighbors' sign-off is never required.
Will an ADU raise the property taxes on my whole house?
No. Your existing home is not reassessed. Only the value the ADU adds is assessed — typically around 1–1.25% of the construction value per year. A $250,000 ADU usually adds roughly $2,500–$3,100 a year in property tax, an amount rental income normally covers many times over.
How long does it take to build an ADU?
Plan on about six months end to end: roughly 1–3 months for design and city permits, then 3–4 months of construction. Garage conversions are usually faster since the structure already exists. City review times vary, but state law caps ADU permit review at 60 days.
Do I need to add parking?
Usually not. Garage conversions require no replacement parking, and new ADUs within half a mile of transit are exempt from parking requirements. Where one space is required, a tandem spot in your existing driveway counts in most California cities.
Can I convert my garage?
Yes — if it was legally built, your garage or other accessory structure can be converted into an ADU, or demolished and rebuilt in the same footprint. Conversions skip foundation and shell work, which is why they're typically the fastest-payback ADU type.
Who handles the permits?
We do. Design, engineering, city submittals, plan-check revisions, and inspections are all handled in-house as part of one fixed-price contract — you approve the plan and we manage the city from first submittal to final sign-off.
Can I sell my ADU separately from my house?
Generally no — an ADU is part of your property and sells with it. Recent state law created limited exceptions that let some ADUs be sold separately as condominiums, but the rules are narrow and depend on your city adopting them. If separate sale matters to you, ask us and we'll walk through what applies to your lot.
What size ADU can I build?
Every California city must approve at least 850 sq ft for a studio or one-bedroom and 1,000 sq ft for two or more bedrooms, and many allow detached ADUs up to 1,200 sq ft. Junior ADUs top out at 500 sq ft. Your lot's exact maximum depends on local rules — we confirm it free before you commit.
Do I have to pay city impact fees?
Not if you build under 750 sq ft — state law exempts those units from city impact fees entirely, which can save tens of thousands of dollars. Larger ADUs pay fees proportional to their size, and we include every fee in your fixed-price quote so there are no surprises.
Find out exactly what your lot allows — free.
Design your ADU in minutes and get a transparent line-item estimate — or talk to a real person about your property, your city, and your numbers.