Fire safety warning issued over zero-compression cavity barriers

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.”