5 Reasons Your Revit Family Looks Wrong in Plan View
The family is placed in Revit and looks good in 3D, but in plan view you see extra lines, cannot adjust the material, can see the floor finish beneath the family, or get a solid white fill that you cannot change. The cause is almost always one of five. I have arranged them in the order that is easiest to check in a project, from imports and project settings to editing the family.

