Protective membrane provision and conditions
During the construction of a new house, providing a protective barrier (i.e. from Radon gas) should be possible by installing a fully sealed radon membrane covering the entire floor area, as well as extending over the external walls.
Diagram HR2 - Typical corner detail for an installed radon membrane
The key areas of concern when installing a radon membrane are as follows:
Radon membrane must be suitably certified.
Radon membrane must be installed in accordance with the certification.
Proprietary ”top hat” seals must be used where membrane is penetrated by service pipes.
Radon membrane must be laid across entire floor and external walls.
Radon membrane must not be damaged during installation.
Seal all tears in radon membrane no matter how small.
Ensure the pipe terminal from the radon sump is identified and permanently marked.
Laps must be sealed fully with appropriate tape.
Protect any area of membrane exposed during construction until permanent cover is in place.
Protecting the radon membrane
Barrier protection principle
Illustrated subsequently are radon membrane and damp proof course arrangements which show the principle of barrier protection. Other arrangement details from radon barrier or DPC manufacturers may also be applied.
Care should be taken to ensure possible differential movement between walls and concrete slabs is minimised and precautions should be provided at wall floor junctions and movement joints.
Avoiding membrane damage
When concrete for the floor is poured, it is essential that the radon membrane is not damaged; special care should be taken when power floating. Damage can be avoided by carrying the membrane at a lower level to the finished floor across the rising wall.
Image - Blinding granular fill to reduce the risk of damage to the radon membrane
All joint and service penetrations must be adequately sealed. As creating gas-tight seals under site conditions is difficult, the use of a prefabricated radon membrane, installed by appropriate fully trained personnel, is recommended by TGD C.
Service pipes with top hat seals
Image - Top hat' seal around a service pipe
It is highly recommended that “top hat” seals as illustrated above are used around service pipe penetrations. Double-sided tape is first placed around the service pipe, the “top hat” is then installed and the clip tightened. Once the clip is tightened, a gas-tight seal is created between the pipe and the “top hat”. Double-sided sealing tape is also applied between the radon membrane and the “top hat”.
Upstands to accommodate settlement
Agrement certs recommend that DPC and radon membrane should not be laid in the same course of blockwork in order to avoid creating slip planes in masonry walls.
Install the radon membrane in accordance with the requirements in its certificate. Generally, the radon membrane is installed with an upstand at the wall/floor junction to accommodate a small amount of settlement (if necessary) as shown.
The radon membrane may be laid flat if it can be predicted with certainty that no settlement will occur during the lifecycle of the building, subject to the requirements of the radon membrane’s certificate.
Gas-tight seals around a water pipes
*Image - Example of gas tight seals *
Double-sided radon-resisting tape being used to seal laps in radon membrane
Image - Double-sided radon-resisting tape being used to seal laps in radon membrane
Ensuring membranes are fit for use
Generally, membranes used for radon protection can be used instead of damp proof membranes in ground floor construction. Independent certification, based on Table 1, by an approved body (e.g. NSAI-IAB), can establish whether a membrane used to protect against radon is fit for use.
Table HR1 - Minimum performance level for LDPE radon proof membranes - Extract from TGD C
