Here is an old thread on crossing windows. I just ran the track in front of the window on my layout. I even took down the back board so I could have more light in the train room.
If the window is used for only light or ocasional ventilation just cover it up with your backdrop. If this window is the only fire egress definitely DO NOT cover it up!! If this is the case you can either make this section of the backdrop removable, or make it out of paper so if you need to get out in a hurry you can just rip it down. Brian
Thanks everyone for the input. This window is only for light in the daytime so my first thought was to cover it with the backdrop, however I did not take into account the "WAF" (Wife Acceptance Factor) sooooo, the window has to be open during the day. . I remember seeing something in MR where they had a shade painted with the backdrop which covered the window when they were operating. I'll go and do some more research. TTFN