Then I insulated the entire structure - top, bottom and all sides including the panel on the side with the doorway. I used one form of insulation on the first one, but used refrigeration insulation on the second dog house. I then covered the insulation with plywood and shingled that for looks as well as durability.
Next, I built a porch large enough for the dog to stretch out on in the summer and attached a roof for shade. I placed the entire house and porch up on concrete blocks so snow could not reach the floor and rain could flow freely under the house and porch.
In the early winter, I took three sheets of heavy plastic and stapled them together on one end. Then I cut strips in each sheet alternating the cuts on the middle sheet so the cuts overlapped. I taped the sheets over the doorway to provide a windbreak. I made sure the dog using the kennel knew how to push through the flaps of plastic. If the dog showed signs of chewing on the door covering, I treated the flaps with Bitter Apple or another nasty-tasting product.
If the winter had progressively colder temperatures during the day, I added additional straw inside the dog house. One winter in the 1970s, the weather was so cold, I stuffed the dog houses with straw. When I came home from work I found the dogs curled up in their kennels, buried in the straw. The temperature inside the kennel was a cozy 80 degrees, all generated by the animal itself and retained by the insulation, straw and door flaps.
Water was my constant worry. I made sure that each dog had a drink before I took them out and provided hot water in their bowls in their pens. My theory was that the water would be cool but not frozen by the time they wanted another drink. Now there are special insulated containers available for supplying water to outdoor animals. Check them out.