it's interesting how some get frostbite... I think if you have blocked drafts and have adequate ventilation so condensation doesn't build up to drip onto combs and a drinking system to prevent wattles from hanging in the water to freeze up after having a simple drink, they should be fine. last year, my Chicken Dome had a gap along the back wall of about 1/4" but ran the length of the 14' arch... in the early part of the Winter, snow would filter through and land on the roosting birds - it worried me enough to move the roosts out a few inches, but once the heavy snow came and stuck, that gap was filled in - so I worried again about melting in the Spring, and dripping icy cold water. I managed to avoid any frostbite, but have reworked the cold weather wrapping to eliminate that gap. there is still plenty of ventilation without it.
K Epp (new page, can't see your post to know if I'm spelling your user name correctly...) those babies of yours are stunning! I have no D'Uccle pullets/hens. but they are at the top of my Spring "will have" list! D'Uccle and Cochin are my fave's. best tempered and such incredibly beautiful birds...