How do I limit Rect masking to one side of a cube? Ie, make sure the backface isn't masked as well? To be clear, I'm not asking about how to limit sculpting to one side of a mesh (ie Brush>Auto Masking>BackFaceMask). I'm trying to mask the windows on the North side of a house and the South side gets masked as well.
Since they're windows, you should be able to automatically create polygroups based on the surface normals. This way you can at least isolate the sides you want to work with and mask the rest.