A Comfort customer has the option to choose either of these: A Rough Opening installation is where the entire window, mainframe, and sashes are removed back to the original wall studs. No trace of the original window will remain. The opening is then reconstructed with the new window installed, and includes a new wood extension jamb, new interior perimeter stops, new interior ranch or colonial style wood trim, a new interior sill or stool if required, new exterior stops and exterior wood casing with a sill, and the complete new wood exterior is then wrapped with newly formed aluminum trim, caulked and sealed, maintenance free!A Retrofit installation is the industry standard and is typically where the operating sash vents of an existing window are removed, but the existing window mainframe remains intact. The new custom sized window, along with its new mainframe and sashes, is then installed into the existing mainframe. There is virtually no disturbance to any existing trim or wall area. Most of the time, a wood stop will be applied to the interior perimeter of the new window and the existing exterior trim is wrapped with formed aluminum trim, caulked and sealed, maintenance free! Note: Glass sizes of the new window will be slightly smaller than the original window.