Well, I do not insulate and keeping chickens in a barn with other animals, like horses, who produce a lot of body heat creates enough heat in the room for chickens to be safe despite ambient temperatures, like putting a bunch of people in a room and suddenly you are hot because you are all sharing body heat.  I do not intend to do anything fancy other than provide a little light in the really dark months.  This is a new system here for me regarding coops as I moved in April and haven't wintered here yet.  The winds this spring were fierce though.  I have a barn basement which I hate (200 year old farm here) that is divided out into 'runs' internally, but then there is a small cottage that serves for the other 'nice' girls who I worry won't get along with some of the bigger chickens.  So far we have harmony-- despite momma chicken chasing the heck out of the ducks.  I told one woman to put toddler socks on her birds heads, like ski masks, but for long term I don't want to do that to a bird if I am not really in love with the breed.  Not knowing what I am headed for regarding the housing here I don't want to keep anyone that has a large comb.  The Delaware rooster is at risk so he is in the barn... but like I said, there is something about that basement that feels like a basement to me despite it being built to hold animals which I don't care for.  Maybe Dorkings aren't for me...?