Cast a short length of PVC pipe of at least 100 mm (4 in.) diameter vertically through the floor slab. If the top end of the pipe is placed away from the centre of the foundation slab, a longer run of PVC pipe will need to be placed horizontally in the coarse gravel and all joints in the pipes should be sealed. The pipe protruding from the foundation slab should be capped and sealed properly to avoid radon entry from the sub-slab area. It should also labelled clearly that it is intended for a radon reduction system.