Butyl Tape is used on all overlaps and joints between the radon barrier and pre-formed components. The double-sided butyl tape that we stock has the best adhesion of any we have used in the past ten years, it is 50mm wide, 15m long and comes in boxes of twelve. Please click on the link below for BRE Guidence on protective measures for new buildings.
We also have a gun applied rubberised bitumen adhesive sealant for the awkward detail. This sealant is particularly useful when connecting to existing walls.