Lots of ADU contractors argue the 10% deposit rule, so here is exactly what California law says. Simplified.
I keep seeing this come up, so let me lay out the actual rule, because half the confusion is people remembering it wrong.
The down payment cap is 1,000 or 10 percent of the contract, whichever is less. That whichever is less part is the whole ballgame. It is not 10 percent flat.
Run the math on a real ADU. Say the build is 200k. Ten percent would be 20k, but 1,000 is the smaller number, so 1,000 is the legal max. On basically any ADU the answer comes out to 1,000 flat, because 10 percent of a six figure job is always way more than a grand. The lesser number wins every time.
So when a contractor asks for 10 percent of a 200k job, that is 20k, and that is 19k over the legal limit. Not a gray area. That is California Business and Professions Code 7159.5.
The cap is only the down payment, meaning the money before any work starts. Once work begins, the builder can bill for completed and inspected milestones, and those payments can be large and totally legal. Nobody is saying a contractor only ever gets 1,000. They are saying no more than 1,000 before a single bit of work happens.
Basically Small money to start, then payments that track the actual work.
If a contractor wants to argue it, the code section is right there. 7159.5.