Hi allI have a strange polygon appear on two corners of a building. I have looked at all aspects of the file and can't discover what is causing this polygon, other than a possible Non planar polygon.If this was the case, how would I solve. If Fsds resolves this problem, which does comfirm the existance of a non planar, it seems to affect the 3 'D' design view, adversely.Check Image below, exists on to corners nearest in the picture.Hope someone understands and can helpRegards Dave

hi all for all those interestedThe problem was a concave polygon at each end, not convex.Thanks to Paul who helped me with this problemRegards Dave