Help: Looking at a duplex and a single family home on 1 lot.

[Alex Boylan]

I'm looking at a a duplex and a single family home on the same lot.  Lot is 50 x 135, which is normal for the area.  Numbers look good.  I'm trying to figure out what I'm missing or not thinking about when buying this type of investment.  If it were a traditional Tri-plex, I would allow my normal protocol but this is unique to me and I feel I'm not thinking of something.  Any advice would be great.