In May I rescued 6 ex-battery hens (one since passed away). My dh built them a really nice coop (approx 5wx8lx4h). It's an insulated, draft-free coop with glass pane windows, perches, three nesting boxes and some floor space covered in shavings to walk around on. It has no ventilation holes, but the small coop door is open all day. My husband has not added any ventilation holes due to fear of drafts. Today I noticed black spots on two of the hen's combs. The hens are severely claustrophic. They do not go into the coop unless to lay (if they don't find a "better" place to lay) or to nest at dusk. They spend most of their time in our shed where we store their grain and straw. They lay their eggs on the bales. As it's dark so very early they're in their proper coop about 14 hours with no ventilation and a frozen water bowl. It's -15 C today. What kind of ventilation holes do we (I) need to add to the coop? I was thinking about drilling some holes in the side of the coop that faces the shed to minimize drafts. How many holes should I drill? Should I cover the holes with mesh? Should I drill holes on more than just the one side of the coop? With the holes affect the birds perched high in the coop. (Two have recently discovered perching and I would hate to chill them). Thanks!! PS I love these birds.