Ground-Gas Verification

Ground Gas Verification


“In the case of development, whether the hazardous gas source is natural or man made, it should be considered an ‘engineering failure’ where such gases are found to be elevated to levels which may cause damage to property or adversely affect the health and wellbeing of users of that development.”

Full gas membrane

Above: Ground-gas membrane installation

What is verification?

Verification is the process which identifies that ground-gas protection measures are meeting remediation criteria, in order to ensure the safety of future site users. The process typically involves inspections and non-destructive tests carried out by trained specialists. All elements should be planned, recorded and reported.


Good practice

Good practice for verification of ground-gas protection measures has been brought together within a new key guidance document (CIRIA C735, 2014). This guidance is written for designers, installers, verifiers and regulators.

GGS staff work to current good practice and GGS particularly values the following 7 points from guidance:

  1. A verification plan should be written at the design stage
  2. Ventilation is considered a very effective first line of defence, but it must be verified
  3. Membranes (and ancillary materials) must be chosen which will survive the construction process & provide suitable future protection
  4. Follow-on trades must be made aware of the purpose of gas membranes to reduce risk of damage
  5. Verification is as important as design and installation
  6. A risk based approach to verification is required and an independent third party should be used for verification to avoid conflicts of interest
  7. Integrity testing should be used as well as visual inspection to demonstrate a gas tight seal is present across the membrane.


GGS Services

GGS carries out independent verification of ground-gas measures. GGS has a team of trained specialists who routinely carry out verification in line with good practice.

GGS provides the following key services:

  • Production of a Verification PlanMembrane patch
  • Visual inspection of gas protection measures
  • Integrity testing (Non-destructive seam tests, air lance and tracer gas testing)
  • Continuous verification monitoring (quantitative demonstration of effectiveness of gas protection systems)
  • Awareness training of site operatives and follow on trades (maximising membrane integrity post installation)
  • On site construction quality assurance (CQA) supervision
  • Verification reporting


Subfloor void monitoring









Above: Continuous subfloor void verification monitoring


GGS sees strength in maintaining regular, clear communication with installers and site managers to ensure ground-gas protection measures are installed to the required specification and to avoid misunderstandings. GGS strives to be flexible in order to work around the time restraints of complex development programmes. Strong communication and flexibility help to avoid construction delays, while ensuring gas protection is installed appropriately, providing safe construction and reducing the developer’s liabilities.

Take a look at our gas monitoring data and service packages here.

Contact us for a to discuss your requirements or to request a quote.