The Masonry Association’s (MA) newly established Technical Committee has issued a warning over the growing use of cavity barriers installed without compression
Describing the practice of installing cavity barriers without compressions as a “foreseeable life-safety risk”, Technical Note TN01/26 released on by the MA on 24 February raises concerns that zero compression cavity barrier systems, now increasingly appearing on UK construction sites, fail to account for the real-world movement behaviour of masonry and framed buildings.
While some such products successfully pass standard fire resistance tests, the Committee argues that these results do not reflect the dynamic conditions encountered throughout a building’s life cycle.
According to the note, “while such products may satisfy laboratory fire test requirements, the Committee has significant concerns regarding their long-term performance under real building movement, settlement, drying shrinkage and construction tolerances.” It adds that “test performance alone is not sufficient evidence of real-world durability or long-term serviceability under conditions of settlement, shrinkage and differential movement.”
Traditional compression-fit cavity barriers are installed with deliberate preload—typically a minimum of 5mm—between the masonry leaf and the structural frame. This preload maintains continuous contact while absorbing the small but unavoidable movements that buildings undergo.
As the Committee explains, “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.”
By contrast, non-compression barriers are fitted to nominal cavity widths and depend entirely on precise alignment at the moment of installation. The note warns that as a building moves over time, “the cavity dimension increases, the barrier does not expand, [and] gaps open at the head or rear face”. It notes that even a 2–3 mm gap is “sufficient to permit fire and smoke bypass”.
Because such gaps form within concealed cavities, they cannot be detected during routine inspections and may remain undiscovered until a fire occurs.
The MA highlights that laboratory-based fire tests are conducted under controlled conditions that do not replicate in-service building behaviour. Completed structures experience “thermal expansion, structural deflection, creep, shrinkage and settlement,” all of which contribute to increasing cavity dimensions.
The note emphasises that movement of “several millimetres” is both normal and expected, especially in concrete frames and masonry walls. Mineral fibre-based fire barrier materials may also shrink over time, further exacerbating the potential for voids if no compression is present.
In its statement, the Committee concludes: “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.”
The Technical Note therefore 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.”
You can access the MA’s Technical Note TN-01/26 here.