Call the Building Dept. in the jurisdiction where the property is located and ask them if the triplex was permitted as a triplex.

I know in some areas the zoning only permits a certain amount of unrelated persons to live in one unit.

And they (state and local governments) are still doing nothing to close the gap on supply, while increasing construction/permitting/carrying costs. 

Pulling proper permits are very important and also understanding the rules and regulations of the township.

I am considering building another structure if county will permit.

The hardest thing I have seen about this is utilities and the permitting.

@Nick Seginowich I don’t know what the energy code is like where you are looking at the house, but pulling a permit for a full re-hab may trigger updating the insulation, air sealing, windows, etc to a higher efficiency (which can be costly).I would make sure to do your due diligence before pulling the trigger

Never pulled permits like he should have and showed me a fake GC certificate.

Never pulled permits like he should have and showed me a fake GC certificate.

Helping to keep permit costs low is the best course of action in my opinion because that will help building in the area.