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.
If you've got the coop dry and ventilated you can try adding bag balm to the comb tips. Vaseline was worthless last winter for us. Bag Balm stays waxy and hardens a bit on the comb as it gets cold. I'm having good luck with it gooped a little thicker on the tips and reapplying each cold night this year.
Hot steamy foods brought out to the coop on a sub zero day steams up and clings to wattles. So even though they love that oatmeal or 1/2 squash out of the oven you really are doing them no favors. Ask me how I know this...LOL
We all have to do what we think is right for our flock by watching them every day. And if that means throwing in some insulation and heat if you've got -30 F with -50 wind chills then do it. I'm doing it. with heat and partial insulation (ceiling, North and west sides) Sunday and Monday I can tell you my coop stayed at -10 degrees and the poop rocks underneath my birds were like granite and there was no frost on my windows on the coop. 11 birds, 7'x6'x6' coop.