ADU Floor Plans and Layouts
What will actually fit is a question about your garage, not about a plan book. The useful starting point is the legal envelope: what the code lets the unit be, and where the fixed points in your existing structure are.
California ADU law was renumbered by SB 477 in March 2024. The sections cited here are the current ones, Gov. Code 66310 to 66342. Local overlays still apply to your parcel, so confirm your specifics with your city building department or San Diego County before finalising plans.
What the rules actually say
- Converting existing space is not held to the 1,200 square foot cap on new ADUs, so the garage footprint is usually the real constraint
- A JADU is 150 to 500 square feet and has to sit inside the residence or an attached garage
- You may add up to 150 square feet beyond the existing structure, for ingress and egress only, which is typically where a new entry or stair lands
- The fixed points that shape a layout are the existing slab, the old garage door opening, and how far the plumbing has to run from the house connection
- A bedroom needs code-compliant egress and the space has to be conditioned, which is what turns a garage into habitable square footage
Common questions
Will a two-car garage fit a one-bedroom ADU?
Often, because a conversion is not capped at the 1,200 square feet that limits new construction, so the garage footprint is what you are working with. Whether a separate bedroom fits alongside a kitchen and bath depends on the actual dimensions and where the plumbing can run. That is what a design consultation measures.
Where does ADU planning actually start?
With a measurement, not a plan. Before an ADU planner can draw anything useful for a conversion, someone has to establish the garage dimensions, where the existing plumbing and panel are, and whether the structure is attached or detached, because that last one decides whether a JADU is even available to you.
Can I use a stock ADU floor plan?
For a new detached unit, often yes. For a garage conversion, less so: the layout has to work around your existing slab, walls, and the old door opening, which is why conversions are usually drawn to the building rather than picked from a catalogue.
What does the extra 150 square feet get used for?
Access, and only access. The statute allows the expansion solely to accommodate ingress and egress (Gov. Code 66323(a)(1)), so it typically becomes an entry or a stair, not extra living area.
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