Those gable vents will help. They maybe cover four chickens' worth of ventilation? Will there be enough roof overhang to keep snow from accumulating and blocking the vents?
In regards to more ventilation... Are the soffits open or closed? Looks like they're closed from the pictures. Having some of them open would create a good amount of ventilation and have it placed up high. And I don't think you'd have an issue of snow accumulation (I'm in south Alabama so I don't know the "doings" of heavy snow
). You could go as far as to create some sliding panels to open, reduce, or close those possible soffit vents. Don't forget to screen the soffit vents if you go that route.
Ventilation is good, draft isn't. Keep all of your winter ventilation up high above the chickens' heads. Summer ventilation is a bit different...they welcome a breeze during the heat...meaning those windows could be larger or maybe leave them as they are and create some larger screened areas on the other two walls. I've often thought that if I lived in a cold climate that I'd design my coop with sufficient upper ventilation to handle things during the winter. But, I'd also have large screened openings in the walls, larger than standard windows. For winter use I would install snug fitting shutters into these openings (probably built from the cutout panels where the large openings were created) knowing that the upper vents were adequate for the chickens. Leave it wide open for summer but in the winter shutter the sides up and let the upper vents do their things. Just my thoughts...
Will the coop have a covered area that the pop door opens to? That would allow the adventurous chickens somewhere to venture if snow gets to be an issue in the full run.
I've spoken of snow...and I'm not sure if you have it much or just really cold temperatures. If you do have snow, have you worked out how your "people" door will work if snow piles in front of it?
Best wishes,
Ed
