Radon Mitigation Plan – GreenBuildingAdvisor

I need advice on radon mitigation. My home was built in the 1940s in the Appalachians of Virginia. It has a dug out basement with a crawl space. The basement portion has a concrete floor, but it does not have a gravel bed under it. Under the concrete is clay. I keep a whole home dehumidifier running in the basement which has a humidistat set at 50%. I ventilate the basement in the winter to keep the radon levels low. I want to eliminate the need to ventilate the basement since it can drive up my heating bill, so I’m planning to put 10 mil plastic down. I bought a glue gun that has a glue designed to adhere to polyethylene, but I also have 9mm thick 3.87 inch wide tape. I have already install a radon fan with a suction over the sump, in two locations in the basement and one in the crawl space. I have already covered the ground in the crawlspace with continuous sheet of 10 mil polyethylene sheeting. I need to decide how to adhere the polyethylene to the base of the brick walls. I was planning to use some butyl tape (3/32” H x ½” W x 50’ L) found in the roofing section of my home improvement store. A radon mitigation professional told me to use sand to weight the plastic down around the sides.

In the basement, the basement walls are about 30 inches wide on average, creating a shelf that is about 22 inches below the ceiling that has fiberglass insulation between the joists. How far from the ceiling do I need to run the plastic on the walls? Should I cover the “shelf” portion and run it up the wall near the ceiling? In the basement, to adhere the plastic to the wall, I was planning to use 1”x2” furring strips with the plastic rolled once or twice on it and nailed into the wall with some small hardened nails with the butyl tape sandwiched between the wall the the plastic on the furring strip. If that seems too cumbersome, my alternative would be to not sandwich the butyl tape and instead pack it in the top edge of the furring strip once it is on the wall.  Do you know of a better method?

Additional questions:

Do I need a drainage material under the polyethylene on the basement floor? Do I put insulation on top of the polyethylene or under it? What type of insulation should I use? I was planning on using XPS foam board or EPS. What thickness? Do I also need to put the foam board on the walls? If the insulation is under the polyethene sheeting, will moisture cause a problem with the insulation? I have read that the temperature differential between the basement air and the floor should be isolated using insulation to reduce the stack effect. I thought that a drainage material would help the suction of the radon from under the plastic, but it is expensive and I don’t know if I need it. As a substitute for a drainage material, would ½ inch pvc pipe with holes drilled in it, placed along the edge of the basement wall and connected to the radon exhaust system be a good idea? The idea would have the ½” pvc loop together so that the suctions is uniform. Do I even need anything under the plastic like the drainage mat or the ½ inch pvc pipes to assist in migrating the radon gasses out the exhaust system? Since there is no gravel bed under the floor, I’m wondering how to do mitigate cost efficiently. Do I need to seal up any cracks before the plastic is placed? It seems redundant to me, but thought that I would ask.  Please help.