I need to put in a radon remediation system under my house. I'm going to close the crawl space vents, do a sealed vapor barrier and put in a dehumidifier. I had already done this and was happy with results (lower humidity in and under house), but did a radon test and it was very high (so I opened the vents for a short term/partial reduction). My research says to put a perforated pipe under the vapor barrrier and pipe to the outside using a radon pump. All I can find is 4" pipe, but that seems large. Is that recommended? Also, if I already have a plastic vapor barrier, is there any danger in putting in multiple layers, such as mold growing between the layers? (obviously the perfed pipe needs to go between the bottom layer and the soil).

Thanks,