30-degree bay windows are 12 to 14 inches deep, and be more but you will also have the added expense of a new header. I've seen some people work on 2-4 section at once, so homeowner can do themselves provided they have the right home improvement tools and do proper research. Often the center window is fixed for larger bays, for the circular bay bay window, my promotion would be for mullions - mullions to me make the bay better. Mullions and Arches - Great Visual Impact architectural possibilities don't end with that helps you to accomplish all the cost connected with your home improvement