Might I say that this thread is all fine and well but there are layers of considerations to be made based on where you live--i.e. your climate (a dry cold like where I live or maritime Northeast or Northwest with moisture laden cold). How many birds do you have in your coop? How tall is your coop in relation to the roosting bars (can humidity keep rising above your birds at their roost level and out the coop) . I think there are rapid weather events where outdoor humidity "Mother nature" is very difficult to fight against before temperature drops...these events are the worst for frostbite. And personally I believe "cold is cold" dry or humid. And this is where breed research for your area (picking the right comb and wattles) is key.
That being said there are basics to dealing with frostbite. And that is keeping things as dry as you can in the coop. removing Poop, regularly will help. Using dry pine shavings seems to absorb moisture from poo better than hay IMHO. Ventilation as Two Crows has said above the birds roosting spot.