Ground Gas Protection measures, which include gas membrane, barriers, development ventilation and ground floor slabs, are often required by local authorities and warranty providers to have independent assurance in the form of verification.

RSK have been verifying gas membranes and gas protection since 2019 and is led by Christopher Larkin who has recently been accredited with the NVQ4 in the Verification of Ground Gas Protection Systems. RSK are also members of the BVC (British Verification Council) and the BGA (British Geomembrane Association). RSK have Engineers across the UK (trained by Neil Salvidge in verification of gas membranes) who are available to meet verification needs across the country.

With respect to the available guidance documents, namely BS 8485-2015 CoP for Gas Protection, CIRIA C735 Good Practice on the Testing and Verification of Protection Systems, BRE 211 (2023) Radon Guidance for Protective Measures for New Buildings, ASTM documents for verification testing procedures and NHBC NF94 Hazardous Ground Gas (an essential guide for housebuilders), RSK have experience with the verification of membranes, barriers and ventilation measures with in depth detailed reporting that will satisfy Local Authority conditions.

Verification Procedures

Site verification should be carried out in accordance with the verification plan and can comprise:

Visual Inspections 

The Engineer will always provide a detailed visual inspection of 100% of all seams/welds/joints as well as the membrane surface (paying particular attention to areas prone to failure), ventilation measures and floor slab. All inspections will comprise the taking of detailed photographs of the workmanship as well as any defects encountered and the remedial measures carried out.

Mechanical Point Stress Test 

This method, carried out in accordance with ASTM D4437-08 (2013) comprises running a blunt instrument along the edge of the membrane to identify any unbonded seams on the membrane interface.

Air Lancing 

Air Lancing, which is also carried out to ASTM D4437-08 (2013), identifies areas of unbonded seams by directing a high pressure column of air from a compressor via a 4.8mm nozzle at a minimum pressure of 345kPa (50 psi) at a distance no greater than 50mm from the seam being tested. Specialist equipment and training are used to ensure this test is compliant with guidance.

Dielectric Testing (Spark Testing) 

This method, carried out in accordance with ASTM D4787-13, involves introducing current to the ground at a voltage equal to the dielectric strength of the membrane. An electrically charged brush is swept over the surface of the membrane. Defects (in the form of pin holes) are identified when an electrical current is formed and an audible alarm is emitted. Note, not all membranes and site conditions will be considered viable for the use of Dielectric equipment, the Verification Plan author should be well versed in these aspects and design the verification procedures accordingly.

Avoiding Additional Costs and Costly Mistakes 

The world of ground gas assessment, protection and verification is beset with obstacles and potential for mistakes which can lead to costly or very costly remedial measures. RSK can guide you through the process from the beginning with intrusive investigations, data collection and analysis, interpretation, Ground Gas verification plans, on site verification and reporting to ensure your development clears all relevant conditions.

If you are reading this and have a site with some problems, RSK can help with the potential re-definition of gas risk (following further data collection and analysis) to advise and verification of retrospective action, we have a wealth of experience in helping sites through these difficult times.

RSK can provide the right materials to avoid any costly damage to the gas membrane or Radon barrier by follow on trades with tool box talks, posters and other materials.

Accreditation and Memberships 

RSK’s Gas Membrane Verification team is run by an NVQ Level 4 qualified person in the verification of ground gas protection, Christopher Larkin, who is contactable for all verification needs at , details of this accreditation are available here

RSK are also working towards becoming part of the Register of Specialists in Gas Protection Verification (SGPV) under the Gas Protection Verification Scheme when applications open later this year

RSK are a full member of the British Verification Council (BVC) and are also an associate member of the British Geomembrane Association (BGA).


The newly issued Radon maps have caused havoc in some areas that now require basic or full radon protection where previously there was no requirement. Whichever protection is required a Radon resistant membrane/barrier should be installed, a common problem we encounter is when a membrane that has not been tested for Radon has been installed, its very important to ensure that the product has been tested and approved for use in a Radon environment. RSK are able to help if you have any concerns or questions.

While it is not a legal requirement to have radon barriers or membranes validated BRE Radon guidance on protective measures for new buildings (including supplementary advice for extensions, conversions and refurbishment projects (2023) states that the Radon Protective Measures Quality Management Record should be correctly followed and completed to ensure contractual responsibility and recommends that the verifier holds CL:AIRE Accreditation, NVQ 4 in ground gas verification of ground gas systems and is a member of the British Verification Council (BVC).


Please note that full radon protective measures require additional measures that aid ventilation such as a radon sump, ventilated sub-floor void and active systems such as fans (depending upon the development).


Testing for Radon is always recommended, whether you or your development is situated in a new radon area, RSK can help guide you through the process of Radon protection at any stage of the development.

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RSK Geosciences is part of the RSK group of companies

The RSK group is a leading integrated environmental, engineering and technical services business offering bespoke end-to-end solutions to a variety of sectors. Headquartered in the UK but with an established presence throughout Europe, Africa, the Middle East, Asia and Australia, RSK helps organisations around the world achieve their business aspirations in a sustainable and efficient manner.