I have not had too much trouble with the cold. I mean, they don't seem to like it, but they do alright in it. I have lost more birds to the heat than the cold. This is winter number 4 for me. I have put Vaseline on those with the really floppy combs and waddles to help prevent frostbite when it is this cold out. I will keep them cooped in tomorrow to preserve the warmth in the coops, but we don't insulate or provide supplemental heat in there. Dry and draft free, as Lapeerian points out, are the key. I don't know much about silkies though, their different feathers might make them more susceptible to the cold (or to a draft). There are some silkie folks on here that will probably chime in on this for you though.