Verification and gas membranes

Verification of remedial measures in the UK construction industry even where planning conditions require it is at best an after thought and occasionally forgotten completely.  Gas protection measures is one such area where commonly the need to provide verification of the gas memebrane is often only recalled when it is realised the handover of the building cannot occur until all the planning conditions are signed-off.  Evidence of the presence of the membrane being laid may come to light yet is often too pawtry to demonstrate that its integrity was maintained both during the installation and the subsequent construction process. Whilst there has been an understanding for many years about the need to maintain integrity of the membrane which is often seen as the last means of defense ( see construction watch points is offered in BRE 414 (2001)‘Protection measures for housing on gas-contaminated land’) concern has persisted that without published guidance on verification, poor installation practice may be accepted due to weak verification planning and implementation.

The first authoritative guidance to plug this gap was published in 2014 by CIRIA – (Report C735) entitled ‘Good Practice and verification of protection systems for buildings against hazardous ground gases.’ This was shortly followed by BS 8485:2015 ‘Code of practice for the design of protective measures for methane and carbon dioxide ground gases for new buildings’ which also addresses verification.  Both these documents see verification as part of the design phase when the specification and verification plan should be determined, as well as the installation stage, although there are some differences between the  two publications.  Furthermore, the NHBC, the primary warranty provider in the UK for new homes, have their own scheme to address ground gas and have provided their own overview of their expectations for verification which can be downloaded at,66000,en.pdf. If you are confused you probably are not alone and to raise the level of knowledge within the industry CL:AIRE has just launched a one day course on the Verification of Gas Protection Systems which looks at the links between BS8485 and C735 as well as setting the verification process in a risk based context.  Additionally, the course looks at the methods and what constitutes good practice with respect to integrity testing. For more information and the full scope of the course and dates see