A VE body is phyically represented by a number of surfaces.
A surface can contain any number of openings (holes, windows, doors) and adjacencies (internal building surfaces that join 2 rooms). Note that openings can not overlap, and openings can not span surfaces. It is perfectly valid for a surface to have an area of 0 where it consists entirely of opening(s) or adjencies (or any combination thereof).
A surface type is derived from its tilt angle and the VE setting for Vertical-horizontal transition angle (VE Model Settings dialog). Similarly, whether a section of a surface is an adjacency is controlled by the Adjacency separation distance.
