We did the proper building of the straw bales with 3 layers of stucco on the inside and outside and the roof is a standard roof with 6 inch deep fiberglass insulation in it and plywood on the underside. Our straw bale root cellar is attached to our house and we can open the door to it to let some of the wood heat in. We also put a little heater in it, on a thermostat to ensure things didn't freeze. We have temperatures of 40 below Celsius.