As you all know the winters in MI can get a bit cold. I am wondering if it is necessary to insulate a coop? I will be building a 5'widex4'longx4'tall coop. I will make sure that it is tight, with no drafts. I am thinking about using the deep litter method. I will have four winter hardy laying hens. Do I need to insulate the coop, or will their body heat keep it plenty warm in there during the cold? Thanks for the help.