The Masonry Association of Great Britain (MAGB) is calling for the fire safety performance of cavity barriers to be considered over the full life of a building, not just at the point of laboratory tests.
MAGB’s newly formed Technical Committee has warned that while zero-compression cavity barriers may achieve compliance in laboratory fire testing, risks may occur over time because buildings are not static systems.
In its first technical note – TN-01/26 – the committee has outlined concerns that barriers installed without positive compression rely on “perfect geometry”.
However, structural frame shortening caused by creep and shrinkage, brickwork settlement, mortar movement, thermal expansion and construction tolerances can all increase cavity dimensions over time.
According to the committee, as movement occurs, even gaps of only a few millimetres may allow flame and hot gases to bypass the barrier.
As these interfaces are concealed once construction is complete, such failures are not detectable through routine inspection, creating significant “life-safety, liability and reputational risk”, the committee added.
The guidance recommends the installation of horizontal and vertical cavity fire barriers with compression – with a nominal minimum preload of 5mm unless greater compression is justified by manufacturer testing – to maintain contact and integrity under long-term movement conditions.
Keith Aldis, chair of MAGB’s Technical Committee, said: “Our first technical note reflects our collective assessment of how buildings behave in reality over time.
“Laboratory fire testing is conducted under controlled conditions, but real structures are subject to settlement, shrinkage and differential movement.
“Positive compression in cavity fire barriers is fundamental to maintaining contact and continuity as that movement occurs. Our guidance is intended to support long-term fire integrity and promote durable, movement-tolerant solutions across the sector.”
