If you're thinking about turning an old garage into an ADU, there's a good chance someone has already told you it won't work.
The garage is right on the fence line. Zero setback. No room to spare.
It sounds like a dealbreaker. Most of the time, it isn't.
The short answer
California ADU law treats converting something that already exists very differently from building something new.
If you're converting an existing accessory structure — a garage, a shed, a workshop — the setback rules that apply to new construction generally don't apply to you.
Oakland's own ADU standards say the same thing. For this type of ADU, the City's table lists side and rear setbacks as not applicable. Not "reduced." Not applicable.
Why so many people get this wrong
The confusion is understandable, because in normal zoning the instinct is right.
Old buildings that don't meet today's rules are usually protected as "legal nonconforming." That protection is tied to the building. Knock it down, and the protection normally disappears with it.
So when a contractor says "if you rebuild, you'll lose three feet," they're applying a rule that's correct almost everywhere else. ADU law is the exception.
What the state actually says
Here's the sentence that matters, from California Government Code section 66314(d)(7):
No setback shall be required for an existing living area or accessory structure or a structure constructed in the same location and to the same dimensions as an existing structure that is converted to an accessory dwelling unit…
Read that middle part again. "A structure constructed." That's new construction. The law is deliberately covering the case where you tear the old building down and put a new one back in exactly the same place.
The same sentence goes on to say that a setback of no more than four feet applies to ADUs that aren't conversions or same-footprint rebuilds. So even outside this pathway, four feet is a ceiling on what a city can ask for — not a starting point.
How Oakland handles it
Oakland sorts ADUs into categories. The one that matters here is Category One.
A One-Family Category One ADU covers three situations: converting space inside your house, converting an existing accessory structure, and rebuilding an existing accessory structure.
That third one surprises people. Demolition doesn't automatically push you out of the category. And the note attached to Oakland's own table spells it out:
For demolition of an existing accessory structure that is reconstructed in the same location and to the same dimensions, there is an allowed addition for ingress and egress of up to one hundred fifty (150) square feet.
There's a second note worth knowing about too. It says Category One ADUs are allowed "even if the existing facility to be converted or rebuilt does not meet the underlying zone's current development standards, such as height limits, floor area ratios, lot coverage or setbacks." That's Oakland saying it in plain terms.
Where the line actually is
Here's the part to be careful about. The exemption depends on staying in the same location and the same dimensions.
Oakland allows one addition on top of that: up to 150 square feet, and only for getting in and out — an entrance, or a staircase to an upper floor.
Go beyond 150 square feet and you are no longer in Category One. The whole structure then has to meet the setbacks that apply to a Category Two ADU.
So the thing that costs you the setback isn't demolition. It's expansion.
That distinction changes how you'd approach the design. If a building needs more headroom, for example, raising the roof would change its dimensions. Lowering the floor inside might not. Same goal, very different consequence.
What this doesn't cover
This is the part we'd rather you hear from us than find out later.
Everything above is about zoning. Setbacks, lot coverage, height limits — the rules about where a building can sit.
It says nothing about the building code, and the building code has plenty to say about a wall on a property line. Fire-resistance ratings. Limits on where windows can go. How you'd even build it when you can't reach the outside face.
None of that goes away because your ADU is Category One. So the honest version is: keeping the footprint is usually achievable. Making that wall work is a design problem, and it's worth solving early rather than at plan check.
What to do next
If you're at the early stage, three things help more than anything else:
- Find out where the property line actually is. Most people are going on the fence, and fences move. If the eaves overhang your neighbor's parcel, that's a different conversation.
- Measure the inside carefully. Ceiling heights, in particular. Whether an upper floor can stay habitable often decides whether the footprint can stay as it is.
- Check your zoning overlays. Oakland has an S-9 Fire Safety Protection Combining Zone with extra ADU restrictions, and there's an active disagreement between the City and the state over how far those restrictions can go. If your lot is in that zone, it's worth understanding before you spend money.