An accessory dwelling unit (ADU) is a self-contained secondary home on the same lot as a primary residence, with its own kitchen, bathroom and entrance. Homeowners across Orange County build ADUs for rental income, multi-generational living, a home office, or long-term property value.

What types of ADUs can you build?

L Square designs and builds detached ADUs, attached ADUs, garage conversion ADUs, junior ADUs (JADUs) up to 500 sq ft, above-garage ADUs, and guest houses or casitas, tailored to your lot, budget and goals.

How long does it take to build an ADU?

Most ADUs in Orange County take about 6 to 12 months from first design to move-in: design and 3D plans in weeks 2–5, permitting and city approvals in weeks 5–13, construction in months 4–8, then final inspection. Garage conversions move faster; custom detached units take longer.

Do I need a permit to build an ADU in California?

Yes. ADUs must follow California state ADU law and local zoning codes, including limits on unit size, setbacks and parking. Many Orange County cities have streamlined ADU permitting, and L Square handles the full permit process as part of every project.

Is building an ADU worth it?

For most Orange County homeowners, yes: an ADU can generate rental income, increase property value, house family members with privacy, and add flexible space, with faster approvals than most new construction.

ADU Guide

Building an ADU
in Orange County.

Q: How much does an ADU cost in Orange County?

Cost depends on size, type, design complexity, finishes and site conditions. A garage conversion is typically the most affordable path, while a custom detached unit with premium finishes sits at the higher end. L Square provides a custom quote based on your lot and goals, with financing options available.

Everything you need to know: types, cost, timeline, permits and benefits, from L Square, a licensed accessory dwelling unit contractor serving Orange County and Los Angeles.

What is an ADU?

An accessory dwelling unit (ADU) is a secondary, self-contained home built on a lot that already has a primary residence. Also called a granny flat, in-law suite, backyard cottage, or casita, an ADU has its own kitchen, bathroom, and private entrance: a complete second home on your property.

Homeowners across Orange County build ADUs for rental income, multi-generational living, a private home office, or simply to add long-term value to their property. Thanks to relaxed California state laws and streamlined local permitting, building an ADU has never been more accessible.

Which type of ADU fits your lot?

Every property is different. We design and build the full range of ADUs, tailored to your lot, budget, and goals. Torn between a separate structure and converting what you already have? Start with detached vs garage conversion.

Detached ADU: A standalone backyard home, fully separate from the main house, the most private and flexible option.
Attached ADU: An addition connected to your existing home, sharing one wall, efficient on tighter lots.
Garage conversion ADU: Transform an existing garage into a finished, permitted living space, often the most affordable route.
Junior ADU (JADU): A compact unit up to 500 sq ft created within your home's existing footprint.
Above-garage ADU: A unit built over a garage to add space without giving up yard.
Guest house & casita: A luxury detached suite for guests, family, or a short-term rental.

Torn between the two most common routes? Read our detached ADU vs garage conversion comparison, or browse ADU floor plans by size.

How much does an ADU cost?

The cost of building an ADU in Orange County depends on its size, design complexity, type, finishes, and site conditions. A garage conversion is typically the most affordable path, while a custom detached unit with premium finishes sits at the higher end.

Rather than a one-size-fits-all number, we give you an accurate, custom quote based on your lot and goals, along with financing options to make your project achievable, with no surprises along the way.

Get your free, custom quote →

How long does it take?

Most ADUs in Orange County take about 6 to 12 months from first design to move-in. Smaller garage conversions move faster; custom detached units take longer due to design and permitting. A typical timeline:

Design & 3D plans: Weeks 2–5
Permitting & city approvals: Weeks 5–13
Construction: Months 4–8
Final inspection & move-in: Final weeks

What permits and legal requirements apply?

Building an ADU in California requires adherence to state ADU law and local zoning codes, including limits on unit size, setbacks from property lines, and parking. The size limits have a state floor: under Government Code section 66321 a city may not cap an ADU below 850 square feet, or 1,000 square feet for a unit with more than one bedroom. Many Orange County cities have streamlined ADU permitting to ease the housing shortage, and recent state laws have made approval faster than ever.

As a licensed ADU construction company (CSLB #1095476), we package, submit, and clear every city correction (structural, energy, and utilities) so you never have to navigate the Orange County planning department alone.

What do you actually gain from an ADU?

Rental income: A long- or short-term rental that helps offset your mortgage in one of California's most expensive markets.
Increased property value: ADUs add livable square footage and attract buyers seeking rental or multi-generational potential.
Multi-generational living: Keep aging parents or adult children close, with independence and privacy.
Flexible space: A home office, studio, gym, or guest suite that adapts to your life.
Faster approval: Many cities streamline ADU permits compared to new construction.
Sustainability: A smaller footprint and energy-efficient design lower long-term costs.

Inside a finished L Square ADU: flexible, light-filled space for living or renting.

The demand is measurable; see California ADU statistics for permit growth across our service area.

Why build with L Square

L Square Construction is a licensed accessory dwelling unit contractor serving Orange County and Los Angeles. We handle architecture, structural engineering, interior design, permitting, and construction in-house: one team, one contract, from your first call to your front-door key.

Every build comes with precision craftsmanship, transparent pricing, and weekly progress updates, so you always know exactly where your project stands.

Licensed · Insured · Bonded · CSLB #1095476

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Book a free consultation with a licensed Orange County ADU builder, and get a custom plan for your property.

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