ADU FAQs

An ADU (accessory dwelling unit) is a complete, independent home on the same lot as a main house — with its own kitchen, bathroom, sleeping area, and entrance. Common names include granny flats, in-law units, backyard cottages, and casitas. California law requires cities to approve ADUs ministerially (by-right), which means a code-compliant project cannot be voted down or pulled into discretionary hearings.

The four main types: detached ADUs (a standalone backyard cottage, up to 1,200 sq ft under state law), attached ADUs (an addition connected to the main home), garage conversions (turning a garage into living space — cities cannot require replacement parking), and junior ADUs or JADUs (up to 500 sq ft carved entirely within the existing home’s walls, with a recorded deed restriction and an owner-occupancy requirement).

Most single-family and many multifamily lots in California qualify. The real question is what your specific lot allows — zoning, setbacks, easements, fire-severity overlays, coastal zones, and sewer/septic capacity all matter. That’s why we start every project with a feasibility check before anyone spends money on design. Call 562.810.1965 for a free consultation.

A standard ADU is a fully independent unit (detached, attached, or a garage conversion) with no owner-occupancy requirement. A JADU (junior ADU) is smaller — capped at 500 sq ft — created within the walls of the existing home, and it requires the owner to live on the property plus a recorded deed restriction. JADUs are the lowest-cost path to adding a rentable space.

Under state law, a detached ADU can be up to 1,200 square feet. An attached ADU can be up to 50% of the main home’s living area, capped at 1,200 sq ft — so a 1,600 sq ft house could add an 800 sq ft attached ADU, with its own kitchen, bathroom, and entrance. Junior ADUs cap at 500 sq ft. Your city may allow the full state maximums — many do — but local overlays (coastal, historic, fire) can shape what’s practical on a given lot, which we confirm during feasibility.

No. California law prohibits cities from imposing a minimum lot size for an ADU, so lot size alone cannot be used to deny your project. If you own a home, you can almost always add an ADU: a small backyard can fit a cozy studio or one-bedroom unit, and a garage conversion needs no yard at all. Other rules still apply — setbacks, height, fire, and utility requirements shape what fits — which is why we check your lot for free before you spend anything on design.

State law caps what a city can require: no more than 4-foot side and rear setbacks for ADUs. That 4-foot rule is what makes ADUs pencil out on smaller lots — a surprising number of backyards can carry a cottage once you apply it. Front setbacks follow the underlying zoning.

Usually not much, if any. Cities cannot require replacement parking when you convert a garage, and properties near transit — bus corridors, rail stations — are often exempt from any added parking requirement entirely. We map your parcel’s transit proximity during feasibility and tell you exactly what the city can and cannot require.

Not for standard ADUs — state law prohibits cities from imposing owner-occupancy on them, so you can rent both the main home and the ADU. Junior ADUs are the exception: they require the owner to live on-site and carry a recorded deed restriction.

No — state law voids HOA bans and unreasonable restrictions on ADUs. An HOA can still enforce reasonable architectural standards, but it cannot prohibit an ADU outright or impose conditions that make one infeasible. If your HOA is pushing back, talk to us before assuming they’re right.

Yes, but they vary. State law sets minimum allowances cities must honor (generally up to 16 feet, more in some configurations and transit-adjacent areas), and local codes add their own layers. Height is one of the first things we check against your zoning during feasibility.

Often, yes. SB 9 lets owners of single-family lots in urban areas build up to two homes on one lot, or split the lot into two parcels — each of which can hold up to two homes, for as many as four where one stood. Approval is ministerial, with no public hearings. A lot split requires an affidavit that you will occupy one of the homes as your principal residence for at least three years, each new parcel must be at least 1,200 square feet, and some properties are excluded, including historic sites and homes occupied by tenants in the last three years. Full guide: SB 9 lot splits and two-unit homes.

A detached ADU can be up to 1,200 square feet; an attached addition can add up to 50% of the main home’s living area, to a maximum of 1,200 additional square feet; a JADU up to 500 square feet can be created within the home. A new detached ADU needs no more than 4-foot side and rear setbacks, and converting an existing garage or structure in the same footprint requires no new setbacks. There’s no owner-occupancy requirement for a standard ADU. Hillside and fire-hazard overlays can adjust these numbers — which is why we verify your parcel before designing. Our guide to ADUs in unincorporated LA County has the full county standards.

It depends on the type, size, site conditions, and finishes. Garage conversions and JADUs are the most affordable paths; detached new construction costs more because it’s a complete small home — foundation, utilities, everything. The biggest cost variables are site work (grading, sewer lateral condition, panel capacity) and the level of finish. We price every project from your actual lot and plans, not from a menu — call 562.810.1965 for a real number on your property.

The most common paths are home equity lines of credit (HELOCs), cash-out refinances, and renovation loans. Some homeowners build in phases or start with a garage conversion to keep the first project affordable. Our ADU Financing Guide walks through the options in detail.

Programs come and go at the state and local level — some cities and counties have offered pre-approved plan fee waivers or ADU incentive programs. Because these change often, check our Financing Guide and confirm current programs with your city or county before counting on one.

State law (SB 543, effective 2026) requires cities to complete ministerial ADU review within 60 days — but the clock only starts once your application is deemed complete. Incomplete submittals reset the clock, which is why getting the submittal right the first time is the single biggest schedule saver. Our permit process guide walks through all 7 steps county by county, with official portals.

Feasibility and zoning check, design and plan preparation (including Title 24 energy docs), permit application through your city or county portal, plan check and corrections, permit issuance, construction inspections, and final inspection with Certificate of Occupancy. See the full breakdown on our ADU Permit Process page.

No — they’re optional, but valuable. About 20 California counties publish pre-approved ADU plans, which skip structural and energy re-review (site-specific zoning and foundation review still apply). Browse pre-approved plans by city or ask us which program fits your lot.

The number-one delay is an incomplete first submittal — it resets the 60-day review clock. After that: unpermitted existing work discovered at plan check, sewer or septic capacity questions answered late, and coastal or historic overlays found after design instead of during feasibility. We front-load all of it.

Most California ADU projects take about 9 to 12 months from plans to keys. Design and site planning usually take about 4 to 8 weeks, permits clear in about 2 to 4 months for most projects, and construction runs about 3 to 4 months for a garage conversion or 5 to 7 months for a detached ADU. Our ADU timeline guide breaks down every phase.

Possibly — your mailing address doesn’t decide it. West Carson uses a Torrance mailing address (ZIP 90502) but is unincorporated county land, and the same is true of pockets around Torrance and Harbor City, Athens and Westmont just north of Gardena, Lennox, Del Aire, and El Camino Village. Check your address in the County Department of Regional Planning’s zoning/GIS viewer, or look at your property tax bill: if Los Angeles County is the permitting agency, you’re unincorporated. We confirm jurisdiction on every feasibility check, and our guide to ADUs in unincorporated LA County walks through the whole county process.

Through whichever government your parcel actually sits in. Unincorporated parcels permit through LA County: the Department of Regional Planning reviews zoning and your site-specific plot plan, and LA County Public Works Building and Safety plan-checks and issues the building permit, with applications and inspections run through the county’s EPIC-LA portal. Parcels inside a city — Torrance, Gardena, Carson, and the rest — permit through that city’s building department instead. The two systems don’t accept each other’s applications, so confirm jurisdiction first.

Yes — for unincorporated parcels, the county publishes three county-owned standard plans you can download free: two 1,200-square-foot one-story designs and an 800-square-foot design. The construction drawings are already plan-checked, and state law gives pre-approved-plan applications a 30-day approve-or-deny decision once the application is complete, instead of 60. You still need a site-specific plot plan, Title 24 energy calculations, and agency clearances — pre-approved covers the building, not your site. Our guide to ADUs in unincorporated LA County lays out how the program works.

One firm handles everything: feasibility, architectural and structural design, Title 24 energy documentation, engineering, permit submittal and corrections, construction, inspections, and final sign-off. No handoffs between an architect, a permit expeditor, and a separate builder — which is where most ADU projects lose months.

All 58 California counties — our own design-build crews cover Southern California and our vetted licensed subcontractor partners extend our reach statewide. Browse our locations to find your county and city.

Yes. ADU Cities is built by Mars Construction Industries Corp, CSLB #1138550 — A General Engineering, B General Building, C-36 Plumbing, and C-20 HVAC. Verify any contractor’s license at cslb.ca.gov before you sign anything.

Yes — permits are part of the job, not an add-on. We prepare the submittal package, file through your city or county portal, respond to plan-check corrections, and coordinate inspections through final sign-off.

Call or text 562.810.1965 for a free consultation. We’ll look at your lot, tell you what it can carry, and give you a straight answer on feasibility before you spend a dollar on design.

Yes. Standard ADUs can be rented long-term with no owner-occupancy requirement — rent the ADU, the main home, or both. The math is why so many owners do it: a one-bedroom ADU renting for about $2,500 a month brings in $30,000 a year — $150,000 in five years — from land you already own. Owners use that income to cover the ADU payment, offset their mortgage, or fund retirement; others house family instead. Our ADU rental income guide runs the numbers in detail.

It depends on your city — short-term rental rules vary enormously across California, and some cities restrict or ban non-hosted STRs. Check your city’s rules on our Can I Airbnb My ADU? page before planning around nightly income.

California has created a legal path for separate ADU sales (AB 1033), but it’s opt-in for local agencies and comes with conditions — it’s not available everywhere yet. If separate sale matters to you, ask us and we’ll check your jurisdiction’s current stance during feasibility.

Yes — a finished, permitted ADU can raise a California home’s value by about 20 to 30 percent. On a $900,000 home, that could mean $180,000 or more in added value. Buyers pay more for a home that comes with rental income or private space for family, and appraisers now count finished ADUs in the total value, weighing added living square footage and rental income potential. How much you actually gain depends on your market, the ADU’s quality, and whether it’s permitted — unpermitted work adds risk, not value. Our guide to how much value an ADU adds breaks down the numbers.

Yes, but only on the new unit — your whole home does not get reassessed when you add an ADU. Proposition 13 still protects your existing base value on the main home, and the county only adds the value of the new construction to your assessment, so you are taxed on what you built, not on a brand-new value for your entire property. For most homeowners that means a modest increase based on the cost and size of the ADU, not a shocking jump all at once. A garage conversion usually adds less than a large detached ADU, because less new construction is involved. We help you estimate the increase before you build, and our ADU property tax guide walks through how it works. For specifics on your parcel, check with your county assessor.

It depends on the ADU type and your utility providers. Some jurisdictions allow or require separate meters; others share service with the main home. We evaluate sewer lateral capacity, water service, and electrical panel capacity during feasibility — undersized infrastructure found late is a classic budget-buster.

Not if your main home doesn’t require them. California law is explicit: an ADU cannot be required to have fire sprinklers if the primary residence is not required to have them — and building an ADU never triggers a sprinkler retrofit on the main house. The rule covers detached, attached, and garage-conversion ADUs. If your main home has sprinklers (most California homes built since 2011 do), the ADU needs them too. Full breakdown: ADU fire sprinkler requirements.

A garage conversion typically takes about 3 to 4 months to build, while a detached ADU typically takes about 5 to 7 months depending on utilities and finishes. Add design (about 4 to 8 weeks) and permitting (most projects clear in about 2 to 4 months) in front of construction, and most homeowners are looking at about 9 to 12 months from plans to keys. Site conditions — grading, utility trenching, panel and sewer work — move the schedule more than the floor plan does. Our ADU timeline guide breaks down every phase.