I have brooder lights in every pen, and I raise silkies and seramas. One serama hen froze to death when she slept on the floor away from the brooder lights and it was 13*. After that, I moved all my seramas into a smaller coop wiith a space heater and brooder lamps. It stays above 35* in there , some are crammed into smaller cages, but I had to get them in that room with the heater, and until the cold snap is over, then I will move them back to their regular roomy pens. I don't want to chance losing another nice hen. Today is supposed to get around 40*, so I will be moving them back to their pens.