Verification and continuous subfloor void monitoring

Verification and continuous subfloor void monitoring

Project title: Lymington Fields, Dagenham

Client: Large Engineering Company

Location: Dagenham, London

Start date: May 2014

End date: January 2015


Services provided:

  • Ground-gas verification services, (including Visual Inspection and Tracer Gas Testing)
  • Subfloor void continuous monitoring

Key benefits:

  • Saved time
  • Reduced costs
  • Meet industry standards


New housing development requires environmental monitoring to meet NHBC standards

Ground-Gas Solutions (GGS) was commissioned by a large engineering company to carry out verification of a large scale building project. The new housing development was planned on being built on potentially contaminated ground; therefore installation of a gas resistant membrane was required on all building plots.

After some investigation, it was discovered that the site was part of a sand and ballast pit from the early 1900s, which later became a landfill with predominately clay fill.  Since being backfilled in the 1950s, the site had been levelled and used as an open public space.

Each development needed a gas resistant membrane; consequently a third party qualified verifier was required to attend the site for the purpose of installation and verification.

Will - 1-2

GGS and site staff install a ground-gas membrane.

GGS was appointed to carry out Integrity Testing on all blocks within Phase 1b of the project. The method applied was Tracer Gas Testing, which is the process of pressurising the area between the block and beam base of the house, as well as the gas resistant membrane. Once the area has been pressurised, a detector is passed over the membrane to highlight any leaks. Where any leaks are detected, repairs are made and the test is repeated until there are no compromised zones.

GGS environmental engineers carried out this process on eight constructed show homes, all of which were discovered to have inadequate gas protection measures in place. As the show homes had failed the verification test, the potential cost of remedial action was in excess of £20,000 per building.

In order to meet National House Building Council (NHBC) standards, GGS proposed a three week remediation strategy using subfloor void monitoring to assess the ground gas risk.

Will - 1

New housing development with continuous subfloor void monitoring.

These remedial actions both satisfied NHBC requirements and saved the client a large sum of money. GGS also involved the site’s ground workers in the membrane installation. This not only added value to the services provided but resulted in a higher quality of workmanship and a reduction of time needed to remediate.

Through identifying the development’s ground-gas risks, applying a remediation strategy and working closely with the client, GGS were able to save the client nearly £150K. Each development block passed with minimal defects.

To find out more about GGS’s gas verification services, click here.