Converting 4-family into 5-family apartment

[Jeffrey Butler]

Hello fellow BPers!

It took me about 5 years to finally make the decision to invest in real estate and now that I feel I'm late to the show, I want to jump in full speed ahead.

I could probably fill this post with thousands of questions and comments about next steps, and how-to's.. But I'll stick to a few most straight forward questions I have about a legal 4-plex property I'm interested in purchasing. 

I'm interested in buying this property as MY FIRST using a private loan with $0 down with rehab included in the loan.

Basically the property is currently a legal 4-plex with 2 illegal apartments in the ground floor both having their own exits. There are 5 electric meters (4 for tenants and 1 for landlord). The landlord's family members are currently staying in the 2 small illegal units. I am thinking about combining them into 1 additional legal unit to make 5 in total.

I am wondering; 

1) how easy/quick/expensive would it be to legally change the property into a 5 unit building? It is located in a "Central Commercial" zoned location where most other properties are either MF or commercial. Property is located in Westchester County, NY.

2) the property is currently not the best deal with 4 units rented out but adding the 5th unit makes it a MUCH better deal. Is this something recommended to do to "create" a deal on a property that would rather be 6% cap rate and $5K cash flow/yr, but when adding the 5th legal unit makes it 9-10% cap and $20k cash flow/yr?

I understand all municipalities are different but I am just trying to gauge how difficult a task it would be and if it would cost an arm and a leg to do.

Any info is appreciated! THANK YOU