Can I Build an ADU on My Property?

Here's the good news up front: under California law, almost every single-family property can have some ADU. Cities can't ban them. So the real question isn't "can I build?" — it's "what can I build, where, and how big?"

Feasibility comes down to six things about your specific property.

1. Lot size and shape. State law doesn't set a minimum lot size for ADUs, so even small lots qualify. But the lot's shape decides where a unit can physically fit. A wide shallow lot and a narrow deep lot with the same square footage can support very different ADUs.

2. Where your house sits. The position of the existing house determines what's left over. A house pushed to the front of the lot leaves a generous backyard; a house centered on the lot may leave only slivers on each side.

3. Your garage. An existing garage is often the cheapest path to an ADU — or the thing standing in the way of a better one. Its location, condition, and whether it's attached or detached all matter.

4. Open space. After you subtract the house, the garage, required setbacks, and any easements, what's left is your buildable area. This is often smaller than the yard looks.

5. Existing structures. Sheds, patios, pools, retaining walls, and mature trees all occupy space or complicate construction. Some can be removed; some (like protected trees) can't.

6. What's under and above the ground. Sewer lines, utility easements, and overhead power lines can quietly remove big chunks of your buildable area — we'll cover these in lesson 2.4.

The feasibility mindset

Think of feasibility as drawing a map of your property with all the "can't build here" zones shaded out. Whatever's left unshaded — that's your canvas. Everything in this module teaches you how to shade that map accurately before you fall in love with a floor plan.