When elements are transparent, only edges and fill patterns (including solid fills) are drawn on element faces.
If you are editing model categories for elements in a linked model
When elements are transparent, only edges and fill patterns (including solid fills) are drawn on element faces. The faces between pattern lines are not drawn. In Hidden Line view and Shaded view, parts of edges are hidden. An edge can be hidden by the face of any non-transparent element, and by a face of its own element (even when it is marked transparent). Edges are not hidden by other transparent elements.
The following images show the same model in 3D view. The second image shows how part of the roof looks when transparency is applied.