Accessory dwelling units — built for California's future.

California's housing shortage has made accessory dwelling units (ADUs) one of the most practical investments a homeowner can make. Whether you need a rental unit, a home office, space for family, or a long-term aging-in-place solution, an ADU adds square footage, flexibility, and value. CaliFirst Remodel designs and builds detached, attached, and garage-conversion ADUs across California, from Los Angeles backyards to Bay Area lots where every square foot counts.

What is an ADU, and what types can I build?

An accessory dwelling unit is a secondary residential unit on the same lot as a primary home. California recognizes three main types:

• Detached ADU: A standalone structure, typically in the backyard.
• Attached ADU: A unit attached to or within the primary residence, often a converted wing or basement.
• Garage Conversion ADU: A converted attached or detached garage.

Junior ADUs (JADUs) are smaller units — up to 500 square feet — created within the existing footprint of a single-family home, usually with a small kitchenette and an exterior entrance. CaliFirst builds all three types, with garage conversions and detached units being the most common in Southern California.

How much does an ADU cost in California?

CaliFirst ADU projects typically range from $150,000 to $400,000, depending on type, size, finish level, and site conditions.

• Garage conversions: $80,000 to $180,000 for a straightforward conversion; more if the foundation, roof, or electrical panel needs upgrading.
• Attached ADUs: $120,000 to $280,000.
• Detached ADUs: $200,000 to $400,000+, especially for larger units with full kitchens, laundry, and premium finishes.

Site conditions that increase cost include sloped lots, limited access for equipment, aging utility connections, septic systems instead of sewer, and required foundation work. We provide a detailed budget after a site evaluation and feasibility study.

How long does it take to build an ADU?

Most ADU projects take 12 to 20 weeks of active construction after design and permitting. However, the full timeline — from first conversation to certificate of occupancy — often stretches to 8 to 14 months because of design, plan check, and utility coordination.

• Design and feasibility: 4 to 8 weeks.
• Permitting and plan check: 8 to 16 weeks, depending on the city.
• Construction: 12 to 20 weeks.
• Final inspections and utility activation: 2 to 4 weeks.

Cities like Los Angeles, San Jose, and Oakland have streamlined ADU processes, but busy plan-check departments and utility backlogs still cause delays. Starting early is the single best way to protect your timeline.

What does California ADU law say about setbacks and size?

State law (AB 2294, SB 9, SB 10, and related legislation) limits local restrictions on ADUs. As of 2026, key rules include:

• Detached ADUs can be up to 1,200 square feet in many cases, though some cities allow larger units.
• Setbacks for detached ADUs are typically 4 feet from side and rear property lines.
• Height limits vary by zoning but often allow up to 16–18 feet for detached ADUs.
• Parking is not required for ADUs if they are within half a mile of public transit or if they convert an existing garage.
• Owner-occupancy requirements have been largely eliminated for most ADUs.

Local cities can impose additional design guidelines, especially in historic districts or hillside areas. CaliFirst navigates both state law and local ordinance for every project.

What are the most common ADU utility considerations?

ADUs need independent or shared connections for water, sewer, gas, and electricity. Common issues include:

• Electrical panel upgrades: Many older homes need a 200-amp panel to support an ADU.
• Sewer lateral capacity: A camera inspection often reveals root intrusion, offsets, or insufficient slope.
• Gas lines: If the ADU has a stove, dryer, or tankless water heater, the gas meter may need upsizing.
• Water pressure: Long runs to a backyard ADU can require booster pumps.
• Solar and Title 24: New ADUs must meet California energy code requirements, which may include solar-ready design or solar panels depending on size and jurisdiction.

We coordinate all utility work and inspections as part of the project.

What materials go into a CaliFirst ADU?

• Foundation: Slab-on-grade, raised foundation, or existing garage slab reinforcement.
• Framing: Wood or advanced framing with continuous insulation.
• Exterior: Stucco, fiber-cement siding, or wood accents to match the primary home.
• Roofing: Composition shingle, standing seam metal, or flat membrane to match the main house.
• MEP: Updated electrical panel, tankless water heater, mini-split HVAC, and energy-efficient appliances.
• Interior: Custom cabinetry, quartz countertops, luxury vinyl plank or tile flooring, and LED lighting.

FAQ

How much does an ADU cost in Los Angeles? Most ADUs in Los Angeles cost between $150,000 and $400,000, with garage conversions on the lower end and detached units on the higher end.

How long does ADU permitting take in California? Plan check typically takes 8 to 16 weeks, though some cities have expedited ADU tracks. Total project timeline is usually 8 to 14 months.

Can I rent out my ADU? Yes. Most California ADUs can be rented long-term. Short-term rentals are restricted in some cities, so check local rules.

Do I need to live in the main house? For most ADUs built after recent state law changes, owner-occupancy is not required.

Will an ADU increase my property taxes? Yes, but only on the value of the new construction. The existing primary home is not reassessed under Prop 13.

Related services

• Whole-home remodeling
• Kitchen remodeling
• Room additions

Begin the conversation

ADUs are one of the smartest additions you can make to a California property. CaliFirst Remodel handles feasibility, design, permitting, and construction. Share your vision and our team will prepare a preliminary site assessment and budget review.