My first year with chickens in northern Vermont. I have 5 26 week old hens - all cold hardy breeds. Their coop is well insulated and winterized - ventilated, straw, protected from wind as best I could (covered their run with a tarp and construction plastic, leaving space for moist air to escape). The roost is below he ventilation. We are having our first below zero night and I'm worried about them. Tell me they will be fine?? They have one nesting box with a thermopeep pad (to prevent eggs from freezing - 3 are laying) and a heated waterer but no other heat. Also, how can you tell frostbite from dirt? My buff orps have whitish/ gray particles on their combs. I can't tell if it's just dust/dirt or frostbite and I don't want to wash them off or rub it to make it worse. Here is one of them - top of the comb looks whitish.