Verification of a retro-fitted radon membrane

Verification of a retro-fitted radon membrane

Title: Verification of a retro-fitted radon membrane

Client: A UK House builder

Location: Weston-super-Mare



  1. A radon barrier that had already been fitted onto a building had been damaged by site workers
  2. Access to the damaged radon membrane could only be gained through removing small amounts of blockwork at a time

Actions taken:

  1. Initial inspection of the radon barrier to establish the extent of the damage
  2. Provision of training, advice and observation for site staff who would carry out the repairs
  3. Ongoing observation and support for newly trained site workers
  4. Provision of a verification report following completion of the project
  5. Provision of a flexible service to allow for six site visits without fixed dates


Verification of a retro-fitted radon membrane



radon membrane verificationThe client informed us that a completed property had a damaged radon membrane. It appeared that when construction was taking place, a site worker had mistakenly cut away part of the barrier leaving the building and any future receptors at risk of exposure to harmful radon gas. GGS specialists were requested by the client to assess the level of damage, train site workers on industry leading repair methods, and then verify the fixed membrane to ensure the repairs were robust.

The difficulty was that the cavity wall could only be accessed through the breeze blocks used to construct the building. This was going to have a significant impact on the progress of applying and verifying repairs.

Challenges and solution

Groundworkers were employed to knock out individual breeze blocks in the areas where there was suspected to be a radon gas risk. This allowed GGS to observe the extent of the damage to the radon proof membrane. The barrier had been cut and was now in two pieces in many parts of the development. The two sides of the radon barrier needed to be reattached by adhering a self-adhesive gas resistant (SAGR) material to the brick work with a heat gun. A layer of waterproof bitumen paint would also be required to form an additional barrier and to allow a better fix to the walls.

Once inspection of the radon membrane was complete, GGS provided training for the groundworkers on industry standard methods of repairing ground gas membranes. Once they began, GGS offered support and guidance on each visit to ensure they were carrying out the work to the highest standard.

radon membrane verificationThe process of repair involved the identification of walls where the radon barrier was or could be damaged at DPC level. One breeze block was removed at a time to allow for observation of any damage. If damage was visible, a second block would be removed so repairs could be applied.

Bitumen-based primer was applied ensuring that it contacted the damaged membrane on both sides of the cavity wall. This was then left for two hours, after which a self-adhesive gas resistant membrane was applied. The membrane was then verified, and the breeze blocks replaced.

Due to the walls being load bearing and structurally integral to the building design, they required four days to set prior to the block work adjacent to them being repaired.  This meant that only a small part of the development could be repaired and observed at any one time.

Once all of the repairs had been made, GGS used a hand picker to check that the SAGR had adhered solidly to the brick work and existing radon barrier to seal the gap and achieve the required protection standards.



  1. radon membrane verificationGGS provided experienced specialists to assess the level of damage to a radon membrane on a completed building with limited access
  2. GGS provided training and observation for site staff for them to apply repairs
  3. GGS verified the membrane to ensure repairs were robust and provided a verification report on completion
  4. GGS provided a flexible service, enabling the client to manage a problem project with ease



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