Cold weather is coming here...but not cold like in the east. Supposedly will get down around 35-40 at night around here. This morning I had to scrape a little ice off the car. Our five chickens are in a garden coop where the henhouse is covered by the roof and some hardware cloth. All around is wood and a few ventilation holes, but it's an open roof. So far they've been pretty good but I'm getting worried that they will be getting cold soon. Should I do a heat lamp? If so, what should the wattage be? The henhouse is small, only around 4x4 feet. Should I cover the top with a tarp or a blanket or something too? WWYD? Thanks!