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In the past, I would forget to check the render both faces box and some pieces of my 3d model would be ghosted. Now that I am trying to get them to ghost, I can't seem to make it happen. I have toggled the box on and off multiple times for the different colors and still can't make that happen. I know there is something I am missing. I am creating the 3d model using 3d slabs, both vertical and horizontal, in DataCAD, and viewing in object viewer in DataCAD.

I suspect you are just testing the model as you go along. The render backface control only works when you apply a texture to the entity. I never found out how you determine which side is invisible.

The material option to Render Both Faces applies whether or not a bitmap texture is also applied. In more-recent versions of DataCAD we have tried to point polygon face normals 'outward'. So, if you create a slab and view it from the 'outside' you'll be looking at the positive, or 'front' face of each polygon. If you view it from the 'inside', you'll be looking at the negative, or 'back' face of each polygon. When you look at the front face of a polygon, the order of nodes, or vertices, is counter-clockwise. When you look at the back face of a polygon, the order of nodes is clockwise.

The default, non-assigned material has the Render Both Faces attribute enabled. You must assign a user-defined material either by Layer, Color, or Entity to render only the front face of a polygon.

Note: You can also use the Polygon Review options in the Sun Shader to determine which way your normals are facing.

Thanks Mark & Nick for the responses. I am trying to show some interior design ideas to a "do it yourself" client. My idea was to draw the floor & walls and new additional interior elements. In creating the existing exterior walls, it was my intent to have the interior surface be the rendered surface so the exterior would ghost when turning the model allowing you to see the new interior past the exterior walls. I am using vertical slabs to create these walls and using "set by left or right side" along the interior side of the wall surface. In placing vertical slabs, there is no perimeter outline, just one stroke to set the wall. Am I wrong in supposing that the side of the wall used to locate it would be the rendered side? BTW, I am still in version 12. Thanks

Go to Evan Shur's Cheap Tricks Ware site and get Bill D'Amico's Normals macro
http://world.std.com/~eshu/ctw/ctwx.htm

It's well worth the money and not only shows the orientation of the normals but allows you to change them.

The polygons that make up a Smart Wall all have faces with normals that point in the same direction. In the case of Smart Walls, draw them in a counter-clockwise direction to cause the positive normals to point toward the center of the room. This is contrary to the way vertical polygons work but that's the way it is. Which side of the wall you select for inside should not matter, though it does change the direction of the normals for the top and bottom wall caps.