Detached ADU

Detached ADUs in Orange County: Costs, Designs & Permits

A standalone backyard home — the most flexible, highest-rent ADU type. Here’s what it costs, how it’s designed, and how OC permitting works.

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A detached ADU is a fully separate home in your backyard, with its own entrance, kitchen and bath. It’s the most private and flexible ADU type — and usually the strongest for rental income and resale. Here’s the cost, design and permit picture.

Why detached

A standalone unit gives tenants (and you) real privacy, commands the highest rent of any ADU type, and adds the most resale appeal because it lives like a true second home.

Costs & sizes

Cost scales with size, finishes and site work — a compact unit is far less than a large, high-finish build. We give you a firm number for your lot rather than a misleading flat figure.

Permits & timeline

California allows detached ADUs statewide and most Orange County cities have streamlined approval. We handle the city submittal and corrections; most detached builds run several months through design, permits and construction.

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Why build with L Square

Design, permits and construction under one roof. L Square is a licensed Orange County design-build team (CSLB #1095476). One contract covers architecture, engineering, city approvals and our own build crews — so your ADU moves on a fixed schedule from first drawing to final inspection, across Orange County and Los Angeles.

01 · Architect-grade design: Every unit is drawn around your lot, light and privacy.
02 · Permit-ready, OC-savvy: We know each city’s ADU rules and clear the approvals for you.
03 · Built once, built right: Our own crews deliver on a fixed schedule, foundation to finishes.

Licensed · Insured · Bonded · CSLB #1095476 · Orange County & Los Angeles

Frequently asked questions

How much does a detached ADU cost in OC?

It depends on size, finishes and site conditions, so we quote after seeing your lot rather than giving a misleading flat number. A smaller, simpler unit costs far less than a large custom build.

How big can it be?

California allows detached ADUs up to 1,200 sq ft, with at least 800 sq ft widely permitted regardless of local rules. The right size depends on your lot and goals.

Detached vs attached vs garage conversion?

Detached is the most private and highest-rent but typically the largest investment; attached shares a wall and suits tighter lots; a garage conversion reuses an existing structure for the lowest cost.

How long does it take?

Most detached ADUs run roughly 6–12 months from first design through permits to move-in, depending on size and city timelines.

Will it add rental income or resale value?

Yes — a legal detached ADU can generate long- or short-term rent and adds livable square footage that buyers value for rental or multigenerational use.

Building an ADU in your Orange County city

ADU rules vary by city — we handle the specifics for your address. Statewide, California allows ADUs up to about 1,200 sq ft with 4-ft side and rear setbacks (CA HCD); your city may add its own details. For the statewide rules, see the CA HCD ADU Handbook.

Irvine ADU rules Anaheim ADU rules Santa Ana ADU rules Huntington Beach ADU rules ADU cost guide All areas we serve

Ready to start
your ADU?

Get a free, no-pressure quote from a licensed Orange County design-build team — and a plan drawn around your lot.