Finishing Basement Floor

I am insulating an attic that has never been insulated. I want to use fiberglass insulation rather than blown insulation. 1. After researching websites and friends, it was suggested that R-38 or higher type insulation is recommended for the upper midwest. Is this correct? 2. The beams in the attic are 2x6's and I need about 640 sq ft. I was wondering would it make sense to use 2 layers of R-19 insulation rather than R-38/R-49 insulation--the first layer with a vapor barrier and the second layer without? Thanks and much help appreciated, jgwoods

I need to install a plastic membrane over a dirt crawl space for radon mitigation. This will have a suction point to pull radon out from under the sealed space. The book says to use "4 mil high-density cross-laminated white polyethylene". This stuff seems only to be available from specialty dealers and it seems to be fairly expensive, about $100 for a 10*100 foot roll. Can I use something else that I might find at a local hardware or building supply store? My crawl space is pretty ragged. There is a lot of debris and rock shards. I don't want to dig the space up any more than necessary. Can I throw something like a cheap blue tarp over the rough sections and then put the sealed barrier on top of that?