Construction loan for new building on owned parcel?

[Bud Dwyer]

I currently own a four plex on a large parcel.  I want to build a 2nd four plex next to it.  Does anyone know the process to put this in to motion?  I guess my main question is, would this void my current 30yr Mortgage and turn it in to a commercial loan?

Other than that I already have a contractor in place who can build it, but I don't know if I need to get plans drawn up from an architect first, or how to start it.  If anyone has done a similar project before or knows what to do, and what potential pit falls to avoid it would be appreciated.