ADU FAQs

General ADU Basics

You should start by determining the ADU type (such as a garage conversion, attached, or detached unit) and confirming the zoning and feasibility for your lot. Next, hire a qualified design-build team; they will prepare complete design and engineering plans and submit a full permit application to the city. Once the building permit is issued, your licensed contractor will prepare the site, construct the ADU according to the approved plans, coordinate and pass the required inspections, and obtain the Certificate of Occupancy on your behalf. For most homeowners, the full process from planning through construction typically takes about 10–12 months, depending on city review times and project complexity.
An ADU (Accessory Dwelling Unit) is a self‑contained secondary dwelling on the same lot as a primary home with independent living facilities (kitchen, bathroom, sleeping and living space) and a separate entrance. ADU types include detached, attached, conversion, and JADU.
ADU stands for Accessory Dwelling Unit. Variants include JADU (Junior ADU), granny flat, in‑law suite, casita, backyard cottage, or secondary suite.
Benefits of building an ADU include rental income, increased property value, multigenerational living, flexible use, tax advantages (depreciation/deductions), and efficient land use. ROI depends on local rent levels, construction cost, and financing.
ADUs enable nearby, independent living with accessible features (no-step entry, grab bars, wider doors), improved safety options, and lower monthly costs compared with institutional care. They also offer flexible, close family support while still preserving privacy.
Yes; state law requires most single‑family jurisdictions to allow ADUs if zoning, setbacks, utilities, and local code are satisfied. Recent state bills remove many parking and owner‑occupancy restrictions, but local regulations still apply.
Most work requires a licensed contractor (CSLB). California does allow “owner-builder” projects, where the property owner takes on the role of the contractor, but these can be complex and risky because they come with strict responsibilities, legal liabilities, and required disclosures. In many cases, you’ll still be required or strongly encouraged to use licensed specialty contractors for work like electrical, plumbing, and HVAC.
A JADU (Junior Accessory Dwelling Unit) is a unit created within an existing primary residence or as an attached structure, up to 500 sqft, with a small efficiency kitchen and a separate entrance. JADUs are also subject to state rules and any additional local regulations.
Affordable options include garage conversions, JADUs, small detached studios (600–700 sq ft), prefab modular units, and converting existing outbuildings. Please note that there are several factors that affect the costs such as site conditions, level of finishes, additional approvals required, and city/county permitting fees.
Focus on converting existing space (like a garage or JADU), keep layouts compact and efficient, and minimize site work, grading, and utility upgrades. Choose durable standard or mid-grade finishes instead of high-end custom options, get multiple competitive bids from licensed ADU-experienced contractors with clear scopes and pricing, and explore available grants or financing to reduce your net cost.

Permitting & Timing

AB 68 requires cities to issue ADU permits within 60 days of receiving a complete application for ministerially approved ADUs; the 60‑day clock begins when the city deems the application complete.

While every project is a bit different, the process usually follows these stages:

  1. Feasibility and zoning check (confirm what is allowed on your lot)
  2. Initial design consultation and budget discussion
  3. Site visit or survey (as needed for as builts, grading, utilities, or setbacks)
  4. Preliminary design (floor plan and basic layout)
  5. Final construction documents (design, engineering plans, and Title 24)
  6. Permit submittal to the city
  7. Permit review and corrections (city comments and revisions)
  8. Permit approval and issuance
  9. Site preparation (demolition, grading, utilities)
  10. Construction of the ADU
  11. Inspections during construction
  12. Final inspection and Certificate of Occupancy so you can legally use the ADU.
Common causes include incomplete applications, understaffed planning departments, technical non‑compliance (setbacks/utilities), title or easement issues, neighbor opposition triggering discretionary review, CEQA/environmental review/additional reviews from multiple local authorities, and utility coordination.

Start early by hiring an experienced ADU-focused design-build firm that begins with a proper feasibility study. Skipping feasibility is one of the biggest reasons projects get delayed or redesigned mid-way. A good firm will confirm what is allowed on your lot, flag red flags early (setbacks, utilities, easements, parking, fire access), and then move into clear, code-compliant drafting. High-quality, well-coordinated plans tend to receive fewer comments, which is the fastest path through permitting.

To reduce delays:

  • Work with an experienced, ADU-focused design-build firm that knows local codes and submittal standards
  • Choose a firm that has a dedicated permit technician and project manager to manage end-to-end coordination, timelines, and schedules
  • Submit a complete application package (plans, calculations, forms, fees, required reports)
  • Schedule a pre-application meeting with planning or building staff, if available & required
  • Coordinate utilities, easements, and site constraints early
  • Respond quickly and clearly to any plan check comments comments
Cities cannot deny a qualifying ADU arbitrarily. For most ADUs, they must approve the project ministerially if it meets state ADU law and all applicable objective local standards. A city can only deny an ADU by issuing a written explanation that the proposal does not comply with those objective standards (for example, due to fire or utility constraints, environmental or health-and-safety issues, or other conflicts with a valid ADU ordinance).

LA timelines vary widely by project and City or County workload. As a rough guide, many ADU projects follow this timeline:

  • Feasibility and zoning review (what’s allowed on your lot), plus design and drafting permit documents: around 6-8 weeks (longer for complex sites)
  • Planning/zoning and building department review (with corrections): roughly 8–10 weeks total, including the City’s time to review and issue plan check comments
  • Permit issuance: once all corrections are cleared, often a few days to a couple of weeks
  • Construction: typically 5–6 months for a straightforward ADU

Overall, many projects run 10–12 months from first concept to move-in, though some finish faster and complex sites or slow responses can push timelines longer.

San Diego timelines also vary by project scope and City or County workload. As a rough guide, many ADU projects follow this timeline:

  • Feasibility and zoning review plus design and drafting: around 6-8 weeks (longer for complex or multi-family ADUs)
  • Planning/zoning and building department review (with corrections): roughly 8–10 weeks total, including the time the City takes to review and issue plan check comments
  • Permit issuance: once corrections are cleared, often a few days to a couple of weeks
  • Construction: typically 5–6 months for a straightforward ADU

Overall, many San Diego ADU projects also run about 10–12 months from first concept to move-in, with faster timelines for simple projects and longer timelines for complex sites or slower response times.

From a complete application, permitting typically takes 2-3 months including the time taken by the City or County to review comments; total project timelines from concept to occupancy commonly range 10–12 months.
Yes – options include fast‑track review for a fee (if your City provides the option), hiring experienced consultants, and ensuring a complete first submission. Please note that expedited processing shortens but doesn’t eliminate required reviews.
Most ADUs need a ministerial planning/zoning clearance plus a building permit (which usually covers structural, electrical, plumbing, and mechanical/HVAC work). The city then carries out inspections at key stages – typically foundation, framing, rough electrical/plumbing/mechanical, and a final inspection – before granting final approval / a certificate of occupancy so the ADU can be legally used.
Local building and planning departments enforce codes and inspect construction; non‑compliance can result in fines, mandated remediation, or loss of occupancy rights.
Keep copies of all plans, permits, inspection reports, certificate of occupancy, warranty documents, and contractor agreements to demonstrate permitted, compliant status at sale.

Costs & Financing

In California, a full custom ADU project (design + permits + construction + utilities) often lands in the $180,000–$450,000+ range, depending on project type, size, utilities, and site complexities:

  • Garage / interior conversions: roughly $180,000–$250,000+
  • New detached or over-garage ADUs: roughly $200,000–$450,000+

That usually works out to about $250–$400+ per sq ft for construction alone, with smaller units and complex sites (hillside, utilities upgrades, high-end finishes) at the higher end. On top of construction, you’ll also need to budget for soft costs like design, engineering, surveys (if required), permits, site work (if required) and utility fees.

In today’s market, most custom, site-built ADUs in California end up around $250–$400+ per sq ft for construction. Bay Area, Los Angeles/Orange County, and San Diego often sit on the higher end of that range, while Central Valley/Sacramento are typically a bit lower. Site conditions (like hillside lots), utility upgrades, and high-end finishes tend to push costs up.
Soft costs are non‑construction expenses (design, permits, engineering, surveys, project management). They typically make up around 15–20% of the overall project budget (sometimes more in high-fee cities). Hard costs are the physical construction costs – foundations, framing, roofing, trades (electrical, plumbing, HVAC), and finishes – and they usually represent the majority of the budget.
Yes. From time to time, state, county, city, utility, and nonprofit programs offer loans, rebates, or grants for ADUs – often targeted to affordable housing, seniors, veterans, or income-qualified homeowners. Availability, amounts, and eligibility vary by jurisdiction and change frequently, so it’s important to check current local programs before you plan on any funding.
Common options include cash, HELOC, cash‑out refinance, construction loans (convertible to mortgage), personal loans, contractor financing, CalHFA or other government programs, private lenders, and investment partnerships.

For most homeowners in California, a realistic starting range for a full custom ADU project (design, permits, construction, and utilities) is around $180,000–$350,000+, depending on size, location, and site conditions.

  • Garage / interior conversions tend to sit at the lower end of that range in simpler, lower-cost areas.
  • New detached or over-garage ADUs usually fall toward the mid to higher end of that range, especially in markets like the Bay Area, Los Angeles/Orange County, and San Diego.

Ultra-low numbers you see online (like “build an ADU for $60k–$80k”) usually assume very basic finishes, unusually favorable conditions, or marketing “from” prices. For a durable, rentable, code-compliant ADU in most of California, it’s safer to plan on at least the low six figures and adjust upward for complex sites, utility upgrades, or higher-end finishes.

Choose a high-quality, ADU-experienced design-build firm that can give you efficient layouts and avoid redesigns. To keep costs down, use pre-approved or build-ready plans where available, keep the footprint simple and rectangular (if possible), minimize custom features and structural “tricks,” and use standard window, door, and fixture sizes. Bundling design within a design-build contract can also reduce duplication, cut down on permit comments, and help you get a design that meets your needs without paying for unnecessary complexity.
DIY can make sense for non-regulated tasks like painting, flooring, landscaping, and some finishes. But structural, electrical, plumbing, and HVAC work generally must be done (or at least permitted) by licensed professionals, especially if you are hiring anyone to help. California’s owner-builder options do exist, but they come with specific restrictions, liabilities, and risks, so you should understand those rules clearly before relying on DIY for major work.
Plan 10–20% contingency of construction costs for unforeseen site conditions, changes, or permitting surprises.
In California, cities and counties cannot charge development impact fees for ADUs smaller than 750 sq ft. For ADUs 750 sq ft or larger, impact fees are allowed but must be proportional to the size of the ADU relative to the main home. Some jurisdictions also choose to reduce or waive fees further as a local policy, so it is always worth checking with your local building or planning department.
Adding an ADU often increases assessed value and property taxes. You should also update homeowners insurance to cover the added dwelling and tenant liability, or get landlord insurance if renting.

Design & Construction

Under California state law, ADUs can be as small as about 150 sq ft if they meet the efficiency-dwelling standards in the building code. However, many cities apply their own practical minimum sizes (often in the 220–400 sq ft range), and it’s hard to design a truly rental-viable unit below about 350–400 sq ft once you include a kitchen, bathroom, and functional living space.

Under California’s state ADU law, most cities must allow at least 850 sq ft for a studio or 1-bedroom ADU and 1,000 sq ft for a 2-bedroom ADU. Many local ordinances allow ADUs up to 1,200 sq ft, but the exact maximum can vary by city, zoning, and lot size. Junior ADUs (JADUs) are capped at 500 sq ft under state law. Always check your local ordinance, as cities can set their own maximums as long as they meet or exceed the state minimums.
There is no statewide limit on the number of bedrooms in an ADU; state law focuses on overall size, not bedroom count. In practice, bedroom count is constrained by square footage and building code requirements for light, ventilation, and egress. As a rough guide, about 500-600 sq ft often supports 1 bedroom, 800–900 sq ft can support 2 bedrooms, and 1,000+ sq ft can fit 2–3 bedrooms depending on layout. Local ordinances, parking, and occupancy rules may also affect what is allowed on a specific property.
Yes, two-story ADUs are allowed under California’s state ADU laws, but they must still comply with state height rules and your city’s local standards. Recent changes (including SB 897) require cities to allow ADUs up to certain minimum heights (for example, taller attached ADUs up to about 25 feet), which often makes two stories possible. However, each jurisdiction can still set its own overall height and story limits, so whether a 2-story ADU is allowed on your lot depends on your specific local code.
Key cost drivers: unit size, type of the ADU foundation type, site access and grading, slope, site work required, utility connections, structural complexity, level of finishes, local labor rates, material costs, code driven upgrades and required engineered solutions.
Don’t undersize electrical/mechanical/plumbing capacity, ignore soft costs outside of the fee of the contractor (such as design, permitting, city fees), overlook insulation,ventilation or soundproofing, ignore privacy or egress requirements, skimp on storage or functional layout, or fail to plan early for utilities and related upgrades, drainage, and access routes for construction and long term maintenance.
Coordinate early with your designer, contractor, and utility providers. Decide whether you want separate meters or shared service for power, gas, and water, then plan clear routes for sewer, water, and electrical lines between the main house and ADU. Make sure to budget for potential panel and service upgrades, trenching, and utility fees, and confirm everything meets local code and utility company requirements.
Including utilities can make the ADU easier to rent and justify a slightly higher advertised rent, but it also means your net income depends on the tenant’s usage. Check local norms (how nearby rentals are structured), estimate typical monthly utility costs, and decide whether to: (1) bundle utilities into a higher “all-in” rent, (2) charge a flat utility fee on top of rent, or (3) meter and bill utilities separately.
Design single‑level units with no‑step entry, wider doorways, accessible bathrooms, lever handles, and space for mobility aids to future‑proof the unit and broaden the tenant pool.
Prioritize durable, low‑maintenance materials, mid‑range appliances, neutral palettes, and high-impact areas like the kitchen, bathroom, lighting, and hardware. Avoid ultra-luxury finishes and overly custom details that drive up cost without meaningfully increasing rentability or resale value.
Look for clear written warranties, including these commonly provided ones: a longer-term warranty on structural elements (often around 10 years) and (2) a workmanship and materials warranty on general construction (commonly 1–2 years), and (3) pass-through manufacturer warranties on products like roofing, windows, and appliances, plus a simple process for reporting and fixing defects.
An experienced project manager coordinates permits, trades, inspections, budget, and schedule, and helps catch issues before they become expensive delays. Without construction experience, trying to manage an ADU yourself can be stressful and risky. You’ll usually get the best results by working with a full-service ADU design-build firm (like Urbatect) that has an in-house project manager and permit coordinator. They handle feasibility, design, permitting, scheduling, and day-to-day coordination so you’re not chasing contractors, managing change orders, or guessing what should happen next.
Choose energy‑efficient, Title 24‑compliant windows sized for egress in bedrooms, balanced daylight and privacy, and durable frames appropriate to local climate.
Communicate design and construction timelines early, address privacy and shading concerns in design, and maintain a tidy, respectful worksite to minimize opposition.
Choose durable, easy-clean materials over delicate ones. Use tile or good-quality engineered/LVP flooring instead of soft woods, durable exterior cladding like fiber-cement or well-detailed stucco, and solid mid-range fixtures and hardware rather than cheap ones that fail early. Opt for low-porosity counters (like quartz over soft natural stone), washable interior paints, and make sure mechanical equipment is placed where it’s easy to access and service to keep long-term maintenance low.
Respect setbacks and privacy, orient key rooms to capture natural light and the best view lines, maintain emergency and fire access, preserve usable yard space, avoid blocking natural drainage or sunlight for the main house, and plan efficient utility runs for sewer, water and power.

Legal, Renting & Market Guidance

California’s state ADU law strictly limits how much parking cities can require. For most ADUs, a city can require at most one parking space per ADU, and even that must be waived in many common situations – for example, if the ADU is within ½ mile of public transit, is within an existing home or existing garage, or when a garage is converted, where replacement parking for the main house generally cannot be required. JADUs inside the existing home typically do not require new parking. Always check your local ordinance and regulations, but in practice many ADUs end up with no additional parking requirement because they qualify for one of these exemptions.
In California, HOAs cannot outright ban ADUs or JADUs on single-family lots just because the CC&Rs say so. Laws like AB 670 make any HOA rule that effectively prohibits or unreasonably restricts a compliant ADU void and unenforceable. However, HOAs do still have a say: they can require you to submit plans and get design approval, and they may enforce reasonable architectural and aesthetic standards (materials, colors, privacy, noise, etc.) as long as those standards don’t prevent or defeat an ADU that complies with state and local codes. In practice, you’ll need to work with both the city/county for permits and the HOA for design approval.
Yes. California law requires cities to allow ADUs on most multifamily properties, but the number, size, and placement are limited by state rules and your local ordinance, so the exact allowance depends on the specific property.
Often no. California’s ADU and JADU rules are designed to create long-term housing, and many cities now prohibit rentals of ADUs for less than 30 days. On top of that, local short-term rental ordinances and HOA rules frequently ban or tightly regulate Airbnb-style use. Always check your city’s rules and any HOA restrictions, and plan on using an ADU primarily for long-term (30+ day) rentals or family use, not as a hotel unit.
ADU rents are mainly driven by location, unit size and bedroom count, and overall condition/age of the unit. Amenities (parking, laundry, outdoor space, storage, A/C), furnishing, whether utilities are included, and lease length (short vs long term) also move the number, as do local rental market supply and demand and rules around pets or occupancy. It is recommended to contact your local real estate agent to find accurate rent estimates for your ADU.
Long-term rentals (typically 30+ days) are generally allowed and are what California’s ADU laws are designed to support. Short-term rentals (like Airbnb-style stays) are much more restricted: many cities either prohibit short term rentals in ADUs or allow them only under strict local short-term rental rules (registration, licensing, owner-occupancy, etc.). Always check your city’s ordinance and any HOA rules before planning short-term use.
Thoughtful ADU design that respects scale, materials and setbacks can add housing supply while preserving neighborhood character; many cities use design standards to ensure compatibility.
Focus on both build cost and future rent. Keep construction efficient (simple layouts, no unnecessary structural complexity), choose high-demand unit sizes (often 1–2 bedrooms), and use durable, low-maintenance finishes with broad appeal. Boost rentability with in-unit laundry, good light, storage, and parking where possible. Speed permitting by working with an experienced ADU design-build team and consider energy-efficient systems that lower utilities and improve net cashflow over time.
A well-designed, properly permitted ADU will usually increase both resale value and marketability, especially in areas with strong rental demand or multigenerational living. Buyers and appraisers tend to pay more when the ADU has clear permits, documented code compliance, and solid construction quality. By contrast, unpermitted or poorly built ADUs can hurt value or trigger price reductions and repair requests during escrow.
Prefab ADUs work best on simple, accessible lots where there’s enough space for trucks/cranes to reach the backyard and the owner is comfortable with standard layouts and finish packages. A custom, site-built ADU is usually better for owners who want the layout, look, and storage tailored to their needs, functionality and the main home. Many ADU design-build firms (including Urbatect) generally recommend custom ADUs in California so they can respond to site constraints, local codes, and long-term value, but it’s smart to get ballpark quotes for both and compare total cost, access feasibility, and level of customization.