Will I also have to replace the window sills currently in my house?
It all depends on the condition of your current window sills and how your existing windows were originally installed.
Most non-impact windows have much smaller aluminum frames. Therefore, it is likely we will have to remove the old window frame to install the new impact-resistant windows, especially if the old windows were installed directly next to the frame. However, in some instances, there is enough space in between to install the new windows without removing the old frame. This is obviously a case by case basis, and we will have to formally inspect your windows before we know whether we have to replace the old frame or not.