Converting duplex into triplex

[Shahaf Matityahu]

Hi Everyone, 

Does anyone have experience converting a duplex to a triplex?
I am considering renovating the basement into a studio apartment. I contacted the municipality to get information about the Zonnig, and apparently the Zonnig is planned for only 2 apartments. Therefore my only way is to apply to the municipality for an update, I want to explore this option but I have no idea where to start..? any info would be appreciated