Chad and I started the thermal wrap these past two weekends. This 4-inch barrier stands 4 feet back from the tire wall and insulates this area. Plastic is attached to the outside of the insulation boards as a vapor barrier to keep moisture out of the house. First we laid plastic down behind the tire wall. We connected two 2" thick insulation boards for 4" of insulation. We started standing the insulation boards up and backfilled the area. Notice the plastic hanging down from the board on the outside. We insulated the cooling tubes in this inner-area so as not to warm the cool air that will be coming through them. Done for now! Next we'll continue with the 2nd, 3rd, 4th, and 5th courses of the tire wall. After about this point, we will continue the thermal wrap vertically and backfill the area again. The thermal wrap will go all of the way up the back of the house and then tilt in to meet the house back wall at the top tire course. This seals in the tire wall and compacted backfill to create a "temperature battery" for our home.