Also, don't forget insurance. Homeowner's insurance is not a deductible expense on "personal use" property. However, if you have one policy that covers both your personal property and your ADU, you can claim the percentage of your insurance that cover's the ADU.
Generally though, I would expect you to have a physically separate insurance policy for the ADU. If so, then the entire cost of that policy is deductible.
The standard homeowner's insurance policy does not cover losses incurred with non-personal use. That's why I would expect you to have a separate policy for the ADU.
