The Importance of Compression in Cavity Barriers

On 24 February, 2026 the Masonry Association Technical Committee issued a Technical Note (TN-01/26) to provide clear industry guidance regarding the use of cavity barriers and, specifically, the increasing use of zero compression cavity barrier products.It indicates that whilst such products may satisfy laboratory fire test requirements, the Committee had significant concerns regarding their long-term performance under real building movement, settlement, drying shrinkage and construction tolerances.

The new Technical Note explains why a compression fit is essential to maintaining fire integrity over the life of a building covering 1. Background 2. How Buildings Actually Move (Structural Frame, Shortening Brickwork and Mortar Movement and Differential Movement) 3. Why Zero Compression Barriers Are Likely to Fail Over Time (Loss of Contact, Shrinkage and Material Relaxation, Tolerance Stacking and Hidden Failure Mode) 4. Why Compression Fit is Essential 5. TN - 01 / 2 and 6 Summary. Extracts below:

"When installed with compression, a cavity barrier is deliberately preloaded between the masonry leaf and the structural frame or slab edge, ensuring continuous contact across the length of the cavity. This compression provides tolerance absorption, allowing the barrier to accommodate construction deviations, mortar settlement, thermal movement, material relaxation and long-term frame shortening without loss of integrity.

"In contrast, a zero-compression barrier is installed to a nominal cavity dimension with no preload and therefore relies entirely on perfect geometry at the point of installation. As the building undergoes normal in-service movement — including concrete creep and shrinkage, masonry settlement and differential movement between structural elements — the cavity dimension inevitably increases, while the barrier itself does not expand to follow this movement. This leads to the formation of open voids at the interface between the barrier and the adjoining structure. Even gaps of only a few millimetres are sufficient to permit the passage of flame and hot gases, allowing fire to bypass the barrier.

Because these failures occur within the concealed cavity, they remain undetectable during routine inspection, presenting a foreseeable and significant life-safety and liability risk. Positive compression is therefore essential to maintain long-term continuity of fire stopping performance over the service life of the building."

"The Masonry Association Technical Committee considers the use of zero-compression cavity fire barriers to be fundamentally incompatible with the long-term movement behaviour of masonry and framed buildings, and therefore a foreseeable life-safety risk. While such products may achieve compliance in laboratory fire testing, test performance alone is not sufficient evidence of real-world durability or long-term serviceability under conditions of settlement, shrinkage and differential movement.

"The Committee recommends that all horizontal and vertical cavity fire barriers are installed with compression, with a nominal minimum of 5 mm unless greater compression is justified by manufacturer testing. Barriers should be mechanically retained in accordance with tested details, and early design coordination must ensure cavity congestion does not compromise the ability to achieve and maintain compression.

"The growing use of non-compression barriers is driven by installation convenience rather than engineering integrity. In an era of heightened building safety regulation, the industry is urged to return to engineering-led, movement-tolerant fire-stopping solutions. Fire safety must be treated as a life-cycle obligation — not merely a laboratory exercise.(summary)"