ADU Basics: What San Diego Homeowners Should Know

Granny flat, casita, backyard cottage, in-law suite — whatever your family calls it, the State of California calls it an ADU, an accessory dwelling unit, and right now it's the most asked-about project in San Diego remodeling. The reasons vary: a place for aging parents, rental income to offset a mortgage, a landing pad for a boomerang graduate, or simply making an underused backyard earn its keep.

The good news is that California and the City of San Diego have spent the last few years making ADUs dramatically easier to approve than they used to be. The better news is that a little orientation up front saves months of wandering.

The three flavors of ADU

Most projects land in one of three categories, each with its own cost and complexity profile:

• Detached — a new standalone structure in the yard. The most flexible and the most private, and generally the most involved to build, since it needs everything a small house needs: foundation, utilities, and a roof of its own.
• Attached — an addition that shares a wall with your house but lives behind its own entrance. A close cousin of a conventional room addition, often the efficient choice on tighter lots.
• Conversion — an existing garage or portion of the house, transformed. Usually the fastest path, with the caveat that older garages often need more structural correction than owners expect.

What your lot will and won't allow

State law guarantees most single-family homeowners the right to build an ADU, but your specific lot still writes the fine print: where it can sit, how tall it can be, how big it can get. Setbacks for ADUs are friendlier than for ordinary additions, and San Diego has been notably generous compared to many California cities — but the analysis still starts with your property lines, not your Pinterest board. If you want a primer on how those constraints work, we broke them down in setbacks, FAR, and lot coverage.

Decide what it's for before you design it

The single best question in ADU planning isn't "how big can I go?" — it's "who is this for, and for how long?" A rental unit wants durability, privacy, and its own utilities. A parents' casita wants single-level living, wide doorways, and a step-free entry. A future-flexible unit wants a layout that can pivot between the two. Each answer pushes the design in a different direction, and choosing early is much cheaper than changing later.

A small house is still a house

An ADU compresses every trade of a full custom home — foundation, framing, plumbing, electrical, Title 24 energy compliance — into a few hundred square feet, which is exactly why the design-build model suits it so well. One team, one set of drawings, one budget carried from sketch to keys — it's how we approach ADUs and every other project, and small buildings reward it more than most.

If a backyard cottage has been living rent-free in your imagination, let's find out what your lot can actually do. Request a consultation or give us a call — we'll give you a straight read on your options before you spend a dollar on drawings.