Grey - White Areas

My question: Why are some areas grey and other white?


white is a front face, blue/grey is a back face…


Thanks John. But I don’t understand why on my model the grey area should be back face. It is on the same level. What does that mean if it is back face?

Your question suggests you are not clear about the SketchUp concept of “front” and “back” surfaces of a face. Every SketchUp face has two sides, one known as “front” and one known as “back”. The default SketchUp material, which is applied to every face as you create the face, paints the front side white and the back side blue/gray (note: depending on your viewing orientation, shading may make the white seem grayish or the gray seem brighter).

One subtlety that may have caught you is that if you draw a face at z=0 (on the red-green plane), SketchUp automatically orients the front side downward. if you draw a face off the red-green plane, SketchUp usually orients the front side upward. So, if the gray areas in your image are on the red-green plane, you are seeing their backs. If the white areas are above the red-green plane, you are seeing their fronts.

You can reverse the front/back orientation of a face by right-clicking on it and choosing “Reverse faces” from the popup context menu.

Edit: You posted a reply to John while I was typing. Are you certain the faces are on the same vertical level? Depending on the sequence of operations when you drew them, SketchUp may have concluded that some of them were oriented differently. As noted, you can easily reverse them. When multiple faces are connected and some of them are the way you want, you can select one that is correct and then choose “Orient Faces” from the right-click menu.

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front indicates the outside of a 3d object and back is really inside…

because it has no thickness, SU has to guess, which it is and sometimes gets it wrong…

steve was quicker, but I’ll leave this anyway…


Ok, that makes sense, thanks a lot. I was clear about the concept of front and back but it seemed strange to me that on z=0 I had on one side a front area and directly a back area…

SketchUp usually orients a z=0 face with front downward based on a presumption that you are going to extrude it upward into a solid. When you do this, the side that was originally pointing up will be inside the solid. SketchUp assumes you would prefer to have the front sides pointing outward, so it reverses the z=0 face. There are times when this logic isn’t what you wanted or needed, and you have to reverse faces manually.