I am really late in posting, but I just wanted to back someone else’s post when they said to do the deep liter method. Leave the poops in it, just turn it every so often and add new fresh bedding on top. The composting poo/bedding combo below will start to decompose and as it does this it will add heat. (Compost gets hot). Obviously you don’t want heavy ammonia scents choking your birds, but the extra litter will insulate the coop floor from the cold ground. I’d insulte the walls as well, as long as it’s covered up with plywood sheeting. I’ve also sometimes made straw bale “boxes” or huts to put my hens in. They don’t like it so much because I didn’t have a roost for them, (could be easily fashioned with a two by four built in between bales) but it was warmer in that small insulated place within the coop.
These two things can raise the heat in your coop about 10 degrees. I’m always amazed how much comfier I feel as I step into my coop in the most fridgid of winter days. Both the bird’s body heat and these other factors make it warmer.
Oh, and flat roosts-like 2 x4 ‘s helps the chickens cover their whole feet with belly feathers. Keeps the ties from the nip of being frost bitten.
I’ve been looking into some “natural” methods of heating- one using compost and the other using aluminum can “solar panels”. When it comes to fridgid winter days, I think flocks just need supplemental heating to keep the bite of freeze off. They seem to do well in 36*F to 50*F. Their feathers make them amazingly adaptable.
For my Seramas, I use large heavy duty packing cardboard boxes modified with doors cut out placed over and outside of pet heating pads. I then use old used torn up ski jackets to cover the whole box plus the openings/doorways to keep the heat in. When winter is done throw out the dusty box. Replace when prepping for winter. Wash the ski jacket and store it for next year. ... I’ve had great luck with this until I got rats in my coop- luckily I had the heating pads off at the time, but the rats had chewed right through the extension cords. So, rats, mice... any critter having a hankering for plastic cord could be hazardous.
Your new coop looks great. I’m so sorry to hear about your misfortune with the last, but so glad to hear your chickens werent harmed.