An accessory dwelling unit (ADU) is a second, self-contained home on the same lot as your house — a backyard cottage, a garage conversion, or a suite above the garage. In Orange County, ADUs are one of the smartest ways to add living space, house family, or earn rental income without moving. Timberline Build Co. designs and builds ADUs across San Juan Capistrano, Dana Point, San Clemente, Laguna Niguel, and the surrounding South Orange County communities.

Call Timberline Build Co. at (949) 229-1692 to talk through your lot and your goals. We will tell you honestly whether an ADU works on your property — and which type makes the most sense.

Types of ADUs We Build

Not every lot suits every ADU. These are the main types, and the right choice depends on your yard, your existing home, and your budget.

Detached ADU: A brand-new, stand-alone backyard home. The most flexible option — you choose the size, layout, and finishes. Best when you have usable yard space.
Attached ADU: An addition connected to your existing home, with its own entrance, kitchen, and bathroom.
Garage conversion: Your existing garage becomes a legal living space. Usually the fastest and most affordable path, because the structure and foundation are already there.
Junior ADU (JADU): A smaller unit (up to 500 square feet) created inside your existing home, with its own entrance and a small kitchen. A good fit when you want a compact space for a family member or a renter.
Above-garage ADU: A new living space built over an existing or new garage. A strong option on smaller lots where yard space is limited.

California ADU Rules, in Plain Language

California law has made ADUs much easier to build in recent years. Here is what it means for you, in plain terms. Rules are set by the state and by your city, and they do change — Timberline confirms the current requirements for your exact address before we design anything.

Your city must allow ADUs. State law requires cities to permit at least one ADU (and one JADU) on a lot with a single-family home. A city cannot deny your ADU just because neighbors object.
Permits move faster. For a complete application, the city must act within 60 days. That does not mean the whole project takes 60 days — design, engineering, and plan corrections take time — but the permit clock is short.
Setbacks are small. A detached ADU generally needs only 4-foot side and rear setbacks, so it fits on more lots than most people expect.
Size limits are generous. A detached ADU can generally be up to 1,200 square feet, and an attached ADU up to 50% of your home’s living area (with a minimum allowance). A JADU is limited to 500 square feet.
Parking is often not required. If your home is within a half-mile of public transit, in a historic district, or you are converting a garage, the city generally cannot require replacement parking for the ADU.
You can rent it out. ADUs can be rented long-term. Short-term rentals (under 30 days) are generally not allowed for ADUs. An ADU is not sold separately from the main house.
Owner-occupancy. The state removed the rule that the owner must live on the lot to get an ADU permit, so you do not have to live in either the main house or the ADU to build one.

Your city’s zoning, your HOA (if any), and your lot’s utilities can add conditions. That is exactly what our site visit is for — we check the real constraints on your property before you spend money on design.

How Timberline Builds Your ADU

We keep the process straightforward and we stay in touch at every step.

1. Site visit and feasibility. We walk your lot, look at access, utilities, setbacks, and the existing structure, and we tell you which ADU types are realistic and what they would roughly cost. If an ADU is not a good fit, we will say so.

2. Design. We design the ADU around how you will use it — a rental, a family suite, a home office, or a place for an aging parent — and around your lot’s constraints. You approve the layout and finishes before we submit anything.

3. Permits. We prepare the plans, engineering, and permit application and work through the city’s corrections with you. You always know where your permit stands.

4. Build. Our crew builds the ADU, we coordinate inspections, and we keep the site tidy and the schedule honest. You get regular updates, not surprises.

5. Final walkthrough. We walk the finished ADU with you, fix anything that is not right, and hand it over ready to live in or rent.

What Does an ADU Cost?

There is no single ADU price — the honest answer is that it depends on the type, the size, the finishes, and your lot. Here is how to think about it.

A garage conversion is usually the most affordable route, because the structure is already standing. A JADU inside your home is also on the lower end. A new detached backyard home costs more, because you are building from the ground up — foundation, framing, roof, and new utility connections. In Orange County, a well-built ADU commonly runs from the low $200,000s for a straightforward conversion into the $400,000s and beyond for a larger new detached unit with higher-end finishes. Those are planning ranges, not a quote.

What changes the number most is size, whether utilities need upgrading (especially the electrical panel and sewer), the level of finishes, and site access. After our site visit, Timberline gives you a line-item estimate for your specific project — so you see exactly what you are paying for before you commit. We do not quote a low number to win the job and then add costs later.

An ADU also adds value to your property and, if rented, monthly income. We will help you weigh the build cost against the rental or family value so you can decide with real numbers.

Is an ADU Right for Your Property?

Most single-family lots in South Orange County can support some form of ADU, but the best type and size depend on your lot. Bring us the address and we will check the setbacks, access, utilities, and any HOA rules, then give you a straight answer. If an ADU is not the right move, we will tell you — and we will tell you what is.

Ready to find out what an ADU would look like on your lot? Call Timberline Build Co. at (949) 229-1692 or contact us to schedule a free site visit and feasibility review. We serve San Juan Capistrano, Dana Point, San Clemente, Laguna Niguel, Aliso Viejo, Laguna Hills, Mission Viejo, and the surrounding South Orange County area.