Transom windows are named as such as they are located around best of a window or doorway’s transom– This is actually the beam that separates the top in the window or door from the remainder of the wall. You’ll really need to set a steel frame with your existing window. https://kylerbtjka.blogprodesign.com/48224610/new-step-by-step-map-for-london-nw1-secondary-glazing-services