REPLACEMENT WINDOWS The Learning Center In most cases, yes. Many older styles of windows, especially those with single glazing, were not very deep. New technology windows have much thicker frames, which means that they project further into the wall of your home, causing the width of the sill to be reduced. When the sill width is reduced, so is the return at the top of the window. This may affect the re-installation of existing blinds or window treatments. This should be discussed with your contractor prior to installation. A good installer will try to keep the window to the exterior as much as possible. However, there is a limit to how far out he can go and still assure proper attachment to the opening and proper weather-tightness in the exterior.     10. Will my new windows have less sill area than my old windows? < back to list of questions about windows 3245 Miracle Drive Murrysville, PA 15668 724-387-2991 PA Contractor ID PA001856