Publicity surrounding these incidences heightened regulatory and public expectations for managing ground gas risks and to assist the house building industry to better address ground gas related hazards, NHBC produced detailed technical publication in 2007 entitled ‘Guidance on Evaluation of Development Proposals on Sites where Methane & Carbon Dioxide are Present.’
The NHBC guidance was well received by regulators and industry alike; but comprehensive advice relating to specific design concepts, expectations for construction and verification approaches remains less prescriptive. To help clarify expectations, NHBC has produced enhanced guidance (Technical Extra; August 2012) that focuses on common design, workmanship and verification essentials. Downloadable copies of this document and NHBC ground gas guidance are freely available free at www.nhbc.co.uk
NHBC experience suggests that one area where improvements must be focused is at the construction site. The gas membrane should be protected as soon as possible after installation and commissioned installers should be selected based on ability to offer the quality and competency of service and standards required. Obviously installed measures should comply with National Occupational Standards and whilst specialist installers work to these standards, a nationally recognised qualification offers the necessary reassurance to the house building industry that the commissioned installer is appropriately skilled.
Construction Skills Council now offers assessment against these national standards and it is envisaged that by 2013 that operatives holding an NVQ level 2 “Diploma in Sub-structure Work Occupations (Construction) - Installation of Gas Membranes”, should install on high gas-risk sites and whilst a Basic Installer’s Card currently exists automatic renewals for this card ceased in January 2012 and will only remain valid until 2017 with the NVQ forming the replacement.
Quality assurance measures should always be considered as part of the installation package. Indeed independent verification, to NHBC’s satisfaction, will always be requested for high risk gas sites before the Buildmark cover for a new home can be issued. However there is a vast array of verification approaches currently available. To aid the house building industry understanding of best practice approach NHBC are collaborating with CIRIA on new guidance relating to this topic. Publication is expected in March 2013 and details on this work can be obtained from CIRIA by visiting (www.ciria.org)
