I built a small Woods coop(6x10) for my 5 chickens. We've been getting temps in the low 30s at night here with daytime temps in the 40s and 50s. When do I close the windows? Do I close both the side windows and the monitor windows?
I'm a little south of you in Indiana. My coop has 4 windows, pop door, ridge vent, and open eaves. Its been 3 years now and they've never been closed. As long as there is not direct drafts blowing on them the cold itself is not as big of a problem as lack of ventilation.
The top windows are closed in late fall. Their function is to vent out excessive heat in summer. Never seen a Woods coop with side windows. I'd close those to prevent draft. The complete open front provides enough passive ventilation in winter.
That's what the design is all about. Deep enough to not have moving air back of coop where roosts are. South facing so top windows provide solar gain in winter and are full open summer to create chimney effect - forces air up and out keeping coop cool.
My Woods-style coop is 6' wide by 10' deep, and has a small window on one side in addition to the top windows and the front windows. I'm in Massachusetts. Over the past 4 years we eventually block the top and side windows with only after the winter storms begin. We do not ever block the front, and sometimes there is a little snow that comes in, which doesn't seem to bother them or impair my deep litter bedding. While that's not a very precise recommendation, it's my anecdote that you can go quite late and be fine.
We did roof the coop with "suntuf" clear corrugated plastic panels to let in additional light and warmth and in winter when I rake the snow off, it does make it much brighter and more pleasant in there.