adding ADU's onto a 4-plex

[Jeorgea Beck]

I'd love some feedback. 

I have a 4 plex (two duplexes on one lot) în unincorporated Contra Costa County that cashflows well. I have a fabulous 30 year loan at 3%. One of my buildings was built in 1895 and needs a new foundation. The county tells me I could add up to 3 ADU's, one in the basement (at the same time as replacing the foundation) and two detached ADU's.

Adding any number of ADU's has the potential to double my current cash flow. Particularly if I make them mid-term rentals for traveling nurses and the like.

Does anyone have experience with ADU's being added to 4-plex's. I realize residential financing doesn't currently allow for this and pulling money out down the road could be more complex or strictly in the commercial lending realm.

Any and all feedback is appreciated!