The Masonry Association of Great Britain (MAGB) has formally launched its new Technical Committee and published its first Technical Note (TN-01/26), addressing the installation of cavity fire barriers and highlighting the importance of compression in maintaining long-term fire performance.
The Committee’s inaugural guidance focuses on the increasing use of zero-compression cavity barriers and raises concerns regarding long-term performance in buildings subject to structural movement, settlement and shrinkage. The publication marks the beginning of a programme of quarterly Technical Notes aimed at strengthening technical leadership and improving lifecycle safety across the masonry sector.
From Laboratory Compliance to Real-World Performance
Technical Note TN-01/26 draws attention to the difference between laboratory fire testing conditions and real building behaviour.
While cavity fire barriers may achieve compliance in controlled fire resistance testing, buildings are dynamic systems. Structural frame shortening caused by elastic shortening, creep and shrinkage, masonry settlement, mortar compression, thermal movement and construction tolerances can all alter cavity dimensions over time.
The Committee’s position is that barriers installed without positive compression rely on ideal geometry at the point of installation. As in-service movement occurs, even small dimensional changes may result in gaps that compromise fire integrity within concealed cavities.
This introduces a lifecycle performance question: not simply whether a product passed a test, but whether the installed system maintains continuity and contact throughout the building’s life.
Expert Commentary: Compression in Cavity Fire Barriers
The following responses were provided by Keith Aldis, Chair of the Masonry Association Technical Committee, for London Construction Magazine.
1. What is the primary risk associated with zero-compression cavity barriers in real buildings compared to laboratory conditions?
Our position is that the chief risk is a loss of long-term contact and continuity due to normal building movement.
Laboratory fire tests are conducted under static and controlled geometries and measurements are taken under simulated conditions which at best present a close approximation of the issues. However, buildings are dynamic systems subject change in dimensions over time.
Examples being reinforced concrete frame shortening (elastic shortening, creep and shrinkage), masonry settlement and mortar compression, thermal movement, build tolerances and in this case, differential movement between frame and cladding (the inner substate or leaf and outer leaf).
On the inner and outer leaf facings of the buildings, movement is accommodated by the installation of expansion & compression joints, positioned at appropriate spacings in accordance with the relevant standard. However, little is done with respect to the movement between the frame and cladding – essentially within the cavity.
Normally a zero-compression barrier is installed to a nominal cavity width with no preload which itself may leave an air gap between either the inner leaf facing or outer leaf facing. When in-service movement occurs, the cavity dimension increases but the barrier does not necessarily expand to follow it. Even small gaps of 2–3 mm can permit the passage of flame and hot gases, allowing fire to potentially bypass the barrier.
Because these interfaces are concealed within the cavity, such failures are typically undetectable during routine inspection. The risk is therefore a foreseeable and hidden life-safety failure mode developing over time.
In contrast, a compression-fit barrier is preloaded against adjoining elements. This preload absorbs movement, accommodates tolerance, and maintains continuous contact on each of the inner and outer leaf facings, over the life of the building.
2. How should designers and contractors account for structural movement when specifying and installing cavity fire barriers?
Structural movement must be treated as a primary design input in all construction.
Design teams & engineers should quantify expected movement, including concrete frame shortening (often 10–30mm over multiple lifts or floors), masonry settlement at each floor level, and differential movement at slab edges and support systems.
A compression fit should be specified, with a nominal minimum preload recommended at 5mm unless greater compression is justified by a manufacturer’s testing. This provides tolerance absorption and maintains seal integrity over time.
Barriers should be therefore mechanically retained in accordance with tested details, and installation should be documented to demonstrate compliance with Building Safety Act duty holder requirements.
3. What is the potential compliance or liability implications if fire-stopping performance degrades over time due to movement?
Under the Building Safety Act 2022, there is clear emphasis on demonstrable, long-term performance and accountability across the duty holder chain.
If a cavity barrier is specified without compression and subsequently loses contact due to predictable building movement, we believe the risk may be considered as foreseeable. Thus, liability exposure may extend to designers, engineers, contractors, product suppliers and building owners.
Concealed fire spread resulting from known movement behaviour could be interpreted as a failure to exercise reasonable skill and care. Professional indemnity exposure and reputational damage to the design team are likely consequences.
We believe therefore that the central compliance question is no longer simply whether a product passed a laboratory-based fire test, but whether the system was engineered to remain effective - as is reasonably practicable - for the life of the building.
A Broader Technical Role
The Masonry Association Technical Committee brings together senior technical representatives from across the masonry supply chain, including brick and component manufacturers, fire barrier and insulation suppliers, façade contractors, structural engineers, warranty providers and training bodies.
According to the Association, further Technical Notes will follow as part of a wider commitment to improving understanding of real-world building performance and lifecycle safety within masonry construction.
TN-01/26 is available via the Masonry Association of Great Britain.
The Committee’s inaugural guidance focuses on the increasing use of zero-compression cavity barriers and raises concerns regarding long-term performance in buildings subject to structural movement, settlement and shrinkage. The publication marks the beginning of a programme of quarterly Technical Notes aimed at strengthening technical leadership and improving lifecycle safety across the masonry sector.
From Laboratory Compliance to Real-World Performance
Technical Note TN-01/26 draws attention to the difference between laboratory fire testing conditions and real building behaviour.
While cavity fire barriers may achieve compliance in controlled fire resistance testing, buildings are dynamic systems. Structural frame shortening caused by elastic shortening, creep and shrinkage, masonry settlement, mortar compression, thermal movement and construction tolerances can all alter cavity dimensions over time.
The Committee’s position is that barriers installed without positive compression rely on ideal geometry at the point of installation. As in-service movement occurs, even small dimensional changes may result in gaps that compromise fire integrity within concealed cavities.
This introduces a lifecycle performance question: not simply whether a product passed a test, but whether the installed system maintains continuity and contact throughout the building’s life.
Expert Commentary: Compression in Cavity Fire Barriers
The following responses were provided by Keith Aldis, Chair of the Masonry Association Technical Committee, for London Construction Magazine.
1. What is the primary risk associated with zero-compression cavity barriers in real buildings compared to laboratory conditions?
Our position is that the chief risk is a loss of long-term contact and continuity due to normal building movement.
Laboratory fire tests are conducted under static and controlled geometries and measurements are taken under simulated conditions which at best present a close approximation of the issues. However, buildings are dynamic systems subject change in dimensions over time.
Examples being reinforced concrete frame shortening (elastic shortening, creep and shrinkage), masonry settlement and mortar compression, thermal movement, build tolerances and in this case, differential movement between frame and cladding (the inner substate or leaf and outer leaf).
On the inner and outer leaf facings of the buildings, movement is accommodated by the installation of expansion & compression joints, positioned at appropriate spacings in accordance with the relevant standard. However, little is done with respect to the movement between the frame and cladding – essentially within the cavity.
Normally a zero-compression barrier is installed to a nominal cavity width with no preload which itself may leave an air gap between either the inner leaf facing or outer leaf facing. When in-service movement occurs, the cavity dimension increases but the barrier does not necessarily expand to follow it. Even small gaps of 2–3 mm can permit the passage of flame and hot gases, allowing fire to potentially bypass the barrier.
Because these interfaces are concealed within the cavity, such failures are typically undetectable during routine inspection. The risk is therefore a foreseeable and hidden life-safety failure mode developing over time.
In contrast, a compression-fit barrier is preloaded against adjoining elements. This preload absorbs movement, accommodates tolerance, and maintains continuous contact on each of the inner and outer leaf facings, over the life of the building.
2. How should designers and contractors account for structural movement when specifying and installing cavity fire barriers?
Structural movement must be treated as a primary design input in all construction.
Design teams & engineers should quantify expected movement, including concrete frame shortening (often 10–30mm over multiple lifts or floors), masonry settlement at each floor level, and differential movement at slab edges and support systems.
A compression fit should be specified, with a nominal minimum preload recommended at 5mm unless greater compression is justified by a manufacturer’s testing. This provides tolerance absorption and maintains seal integrity over time.
Barriers should be therefore mechanically retained in accordance with tested details, and installation should be documented to demonstrate compliance with Building Safety Act duty holder requirements.
3. What is the potential compliance or liability implications if fire-stopping performance degrades over time due to movement?
Under the Building Safety Act 2022, there is clear emphasis on demonstrable, long-term performance and accountability across the duty holder chain.
If a cavity barrier is specified without compression and subsequently loses contact due to predictable building movement, we believe the risk may be considered as foreseeable. Thus, liability exposure may extend to designers, engineers, contractors, product suppliers and building owners.
Concealed fire spread resulting from known movement behaviour could be interpreted as a failure to exercise reasonable skill and care. Professional indemnity exposure and reputational damage to the design team are likely consequences.
We believe therefore that the central compliance question is no longer simply whether a product passed a laboratory-based fire test, but whether the system was engineered to remain effective - as is reasonably practicable - for the life of the building.
A Broader Technical Role
The Masonry Association Technical Committee brings together senior technical representatives from across the masonry supply chain, including brick and component manufacturers, fire barrier and insulation suppliers, façade contractors, structural engineers, warranty providers and training bodies.
According to the Association, further Technical Notes will follow as part of a wider commitment to improving understanding of real-world building performance and lifecycle safety within masonry construction.
TN-01/26 is available via the Masonry Association of Great Britain.
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Expert Verification & Authorship: Mihai Chelmus
Founder, London Construction Magazine | Construction Testing & Investigation Specialist |
