Frostbite prevention is centered around low humidity levels in the coop, and not insulation.
There should be good airflow through tha tcoop, regardless of temp.
Our coop is insulted on 3 walls, but the rest is left single walled.
Bedding is frozen solid all winter, so we just keep adding dry hay on top.
WHen it hits 30 below, we have a small ceramic heater running, along with a regular 60 watt bulb hanging near the floor, so that the temp comes up a few degrees.
They get more shelter then the wild birds, but that does not mean that they require it.
We also allow for only 4 nest boxes with 40 birds, to ensure no frozen eggs.