My chooks have had less colds in the severe low temps than in the mediocre temps. Chickens can stand a lot of cold if they are well fed and roost in decent dry, ventilated housing with minimal (pref no) draughts. Add maize to the diet to give them central heating. Use vaseline on their combs and wattles if they risk frost-bite.
Ensure they can get out of the wind and out of the wet and they should stand the winter better than you.
Last year I was going to insulate the houses but it was not necessary. I also introduced a heat lamp which sent them crazy with fright and so abandoned it.
On freezing cold nights I have a board which fixes over the large expanse of mesh between house and scratching shed and this stops a lot of excessive airflow. I remove it in the day to air and drive out damp.
Dry, well fed, well sheltered, healthy chooks will come to little harm through cold.