Product category:
Walls
News Release from: Cavity Trays | Subject: Cavity barriers
Edited by the Buildingtalk Editorial
Team on 25 May 2006
Cavity Barriers protect against methane
or radon
Radon and Methane cavity barriers and gas-grade oversite membranes are detailed in the latest Cavity Trays manual.
What happens if you overlook building-in the protection measures required when construction on ground identified as methane or radon emitting? On a site in Herefordshire that is exactly what happened, and the consequential upheaval was both costly and time-consuming
This article was originally published on Buildingtalk on 16 Jun 2003 at 8.00am (UK)
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The development of new homes was on ground that had previously been identified as emitting methane gas.
Aware of the situation, the contractor had constructed the first phase incorporating a dpc methane oversite membrane.
The barrier protected the entire oversite of each unit, but terminated against the inside face of the internal block work skin.
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After completing the external walls, the contractor realised the methane protection should have continued through the external cavity wall skins also.
The absence of cavity barriers meant there was nothing in place to prevent methane gas rising in the cavities and permeating the building envelope.
The houses did not comply with regulations and furthermore presented a most serious potential danger.
He contractor faced two options.
He could take down the new structures to slab level and rebuild.
Alternatively he could attempt to introduce the missing gas-control measures into the existing walls.
He selected the latter.
Special methane protection cavity barriers were preformed for insertion into the external walls.
It was necessary for the contractor to break out the external and internal skin in sections, to permit the preformed barriers to run through the entire cavity wall and unite / overlap the oversite membrane.
All laps between cavity barriers and between barriers and membrane were sealed using a wide gas grade sealing strip.
The barriers were stepped in profile within the cavity, so rainwater penetrating the external skin was arrested and discharged out of the structure via Type W caviweeps / cavivents.
Below the barrier level at specified intervals in the external skin, high performance cavibricks were installed.
These were built in without sleeves or ducts so rising gas was directed out of the cavities, away from the structure.
The arrangement established a ground level integrity shield against rising gas, effective throughout the walls and floor.
It was a costly exercise for the contractor, involving much labour and disruption of the building programme - especially as both cavity skins had to be disturbed.
Subsequent phases of the site were constructed with linking methane cavity barriers built-in at the appropriate stage in construction.
An exceeding easy and straightforward undertaking, and a low-cost one, as long as you remember such barriers must be built-in at the right stage in construction! Radon gas emitting sites require similar protection measures.
Currently the requirements can vary from region to region.
It is always in the interests of the builder or contractor to determine the measures necessary prior to commencing work.
Contact should always be made with the Local Authority for guidance and instruction.
Radon and Methane cavity barriers and gas-grade oversite membranes are detailed in the latest Cavity Trays manual number 17.
Copies available now.
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