You can use Split Face on any non-family instance. The Split Face tool splits the selected face of the element; it does not change the structure of the element. After splitting the face, you can use the Paint tool to apply a different material to this section of face. See Applying a Material to the Face of an Element.
In the conceptual massing environment, a surface can host subregions that have their own properties. Creating subregions can help you refine your design and improve the accuracy of an energy analysis. You can assign a material to a subregion or extrude its profile into a solid or void form to change the topography of the surface.
A wall with a split face (around the window) before painting
A wall with a split face (around the window) after painting
To split a face
Projection type examples
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Top down is useful for drawing skylights.
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Parallel to level is useful for drawing windows.
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In the following example, the wall around the window is split, so that it can be painted to match the border around the door.