ADU Builder in Orange County & Los Angeles

An accessory dwelling unit (ADU) adds a complete second home to your lot: for family, for rental income, or for a home office or guest house. IA Builders is a licensed general contractor based in Culver City, and we build ADUs, junior ADUs and garage conversions across Orange County and Los Angeles.

Types of ADUs

Detached ADU

A separate, standalone building in the backyard with its own entrance, kitchen and bathroom. It offers the most privacy and the most flexibility in layout, and it's the most involved to build: new foundation, utilities run from the main house or street, and a full set of plans.

Attached ADU

Built as an addition to the main house, with its own entrance. It can make sense on lots where the backyard isn't deep enough for a detached unit, and it shares a wall with the house.

Garage conversion

Converting an existing garage into a living unit. The structure, slab and roof are already there, which usually makes a garage conversion the most cost-effective way to add an ADU. The work includes insulation, a new floor system or slab work as needed, windows, plumbing for a kitchen and bathroom, and often upgraded electrical service.

Junior ADU (JADU)

A smaller unit created within the existing house, usually by converting a bedroom or part of the home. Under California law a JADU can be up to 500 square feet, needs its own entrance and an efficiency kitchen, and can share a bathroom with the main house. In most cases the owner has to live in either the main house or the JADU.

How California ADU rules help

California has passed a series of state laws that make ADUs much easier to build than they used to be. In general terms:

• Most single-family lots can have an ADU, and many can have a junior ADU as well.
• Cities can't use local rules to block an ADU of at least 800 square feet with 4-foot side and rear setbacks.
• Cities must review a complete ADU application ministerially (no public hearing) and approve or deny it within 60 days.
• ADUs of 750 square feet or less are exempt from impact fees.
• Garage conversions generally don't require replacing the lost parking.

Each city then has its own ADU ordinance on top of state law, covering details like height, design and coastal-zone requirements, and HOA rules can apply too. We check the rules for your specific lot before you commit to a design.

Our ADU process

1. Feasibility. We look at your lot, the location of the sewer and utilities, access for construction, and which type of ADU fits. This is where we flag anything that changes the budget, like a long sewer run or an electrical service upgrade.
2. Design and plans. We coordinate architectural drawings, structural engineering, energy calculations and, where needed, a soils report.
3. Permits. We submit to the city, respond to plan-check comments, and handle any coastal-zone or HOA steps that apply.
4. Construction. Foundation, framing, utilities, roofing, insulation and finishes, inspected at each stage.
5. Final inspection and certificate of occupancy, so the unit is legal to live in or rent.

ADUs often go hand in hand with other work on the main house. See room additions and whole-home remodeling.

What affects the cost of an ADU

• Type: garage conversion, junior ADU, attached or detached
• Size and number of bedrooms and bathrooms
• Distance to sewer, water, gas and electrical connections, and whether the main panel needs an upgrade
• Site conditions: slope, soil, access for equipment
• Finish levels for the kitchen, bathroom and flooring
• City fees, school fees and any utility connection fees

Frequently asked questions

Can I build an ADU on my property?

Most single-family lots in California can have an ADU under state law, but lot size, easements, utilities, coastal-zone rules and HOA requirements affect what type and size fits. We'll check your lot at the feasibility stage.

Is a garage conversion cheaper than a detached ADU?

Usually, because the foundation, walls and roof already exist. The condition of the existing slab and framing, and how far plumbing has to run, make the biggest difference.

Can I rent out an ADU?

Generally yes, though state law and many cities don't allow short-term rentals of ADUs, and junior ADUs usually come with owner-occupancy requirements. Check your city's current rules; we can point you to them.

How long does it take to build an ADU?

Plans and permits usually take longer than people expect, and city review times vary. Construction time depends mostly on the type: a garage conversion or junior ADU is faster than a new detached unit. We give you a schedule once we've seen the lot.

How much do I pay upfront?

California caps the down payment on a home improvement contract at $1,000 or 10% of the contract price, whichever is less. The rest is paid on the schedule written into your contract, and any change to price or scope needs a signed written change order.

Last reviewed October 2026