Converting triplex into fourplex

[Eduardo Chavez]

Good afternoon, 

I own a triplex in an unincorporated area in Los Angeles County. I am looking into converting it into a fourplex by converting a detached garage into an ADU. I'd love to hear what the process was like from those who have done this as of late in Los Angeles County. Do I contact my local planning department to find out if my property is eligible for this ?