Our site is in a Radon protection area. So I’ve fitted the radon barrier under the insulation, I assume I’m correct to bring the radon barrier up the basement walls to ground level. If so, why would the architect specify a separate tanking membrane? Surely in only need one water and gas tight membrane?

don't think DPC or radon barrier is certified for a tanking application tho.

We had something similar (potential for Methane). The barrier was specified for under the slab only as I'm guessing that any gas in the ground will travel upwards and not laterally? 

 

Turning this the other way round, would a waterproofing membrane give protection against radon?

 

Also, if you're using an external membrane, what protection are you using to ensure it does not get damaged on backfill or if stones are pushed the membrane due to ground movement?