Why Fire Rated Cavity Closers Are Essential for Modern Safety and Confinement

Fire rated cavity closers are essential for modern building safety. They play a critical role in preventing the spread of fire and smoke through cavity walls, ensuring the safety of building inhabitants. However, their effectiveness is highly dependent on correct installation and adherence to best practices. By understanding and addressing the real-world challenges of construction tolerances, builders can ensure that these critical components perform as intended, providing vital protection in the event of a fire.

Buildings should be constructed to eliminate or minimise, as much as possible, all potential fire and fire safety risks likely to arise. The building and its inhabitants should at all times be suitably protected. In theory, this should be a fairly straightforward undertaking, but in practice, the building envelope can present both designer and builder with considerations that are not always immediately obvious.

Understanding Cavity Wall Construction

Cavity wall construction relies on the external leaf (that can become saturated with rain) from not coming into contact with the inner leaf that is required to keep dry. Wall ties are shaped to structurally link the skins and prevent rain tracking across to the inner leaf. The cavity successfully separates and isolates the two. However, in the event of a fire, both air and fire can be drawn through the cavity within all the external walls of the building, fueling combustion. This raises the question of whether there is an optimum way of protecting the external envelope at one of the most frequently occurring features—where it is punctuated by window and door openings. Such openings present the designer and contractor with the usual heat-loss and damp-transference considerations, but with multi-occupancy and numerous other structure categories, there is also the additional important requirement to protect against fire and fire transference.

The Role of Fire Rated Cavity Closers

Fire-resistant cavity closers are an accepted way of addressing window and door reveals. A typical closer contains a non-combustible thermal and fire-resistant core that straddles the cavity, effectively linking both skins. Such closers provide passive fire protection. Applied to all four sides of an opening, the completed installation provides a level of fire resistance, commonly 30 or 60 minutes.

Testing and Standards for Fire Rated Cavity Closers

To establish the number of minutes, closers are subjected to testing at a fire research station. Such stations do a good job, and accordingly, best practice construction is witnessed. Products interface squarely, correctly, and consistently. However, if one looks at the actual on-site building tolerances, they are different, prompting the question of whether currently accepted site tolerances adversely affect the performance of fire-resistant cavity closers.

Are such tolerances compatible with those required with a fire-resistant closer, bearing in mind closer and masonry must interface consistently and without gaps, to perform? Construction tolerances accepted by various authoritative bodies vary, but in general buildings, the following are commonly witnessed:

• Fire Rated Cavity Closer Installation: The optimum performance of any fire-rated closer is dependent on correct incorporation. Put simply, the relationship between a fire-resistant closer and masonry should match those under which the test results were achieved. Cavity wall openings constructed to the varied tolerances shown above differ from those used by testing stations and are unlikely to replicate the test results.

Testing stations qualify their test results relate only to the behaviour of the specimens of the elements of construction under particular conditions of test and do not reflect actual behaviour in fires. All openings in cavity walls should be formed squarely and uniformly, observing best practices to fulfill the objectives and requirements of Building Regulations Approved Document Part B.

• Materials and Longevity: While functionality relies on continuous interfacing, core longevity can be aided with the use of stainless-steel metal ties as opposed to plastic ties securing the closer to the masonry. Metal ties that project through the closer body and continue into the actual protective core itself can extend the period the resistant core is anchored and held in position when fire is attacking with continuous interfacing and retention being the objectives.

The building fabric should be constructed so that there are ‘no reasonably avoidable gaps within various elements, at the joints between elements, and at the edges of elements such as those around window and door openings,’ as stipulated within L1A 5.9.

• Fire Rated Cavity Closer Considerations: Fire testing establishments and bodies such as the BBA quite understandably do not provide warranties. It is down to those constructing the building to aspire to the highest standards to get it right. While one continues to witness variable masonry tolerances, one questions whether building envelope fire resistance will actually provide the intended level of protection in the event of a serious fire. Compliant construction should leave nothing to chance.

A site agent of many years standing poignantly summed up the situation: ‘When you buy a new car, the manufacturers often claim it can travel an impressive number of miles per litre, and I do not doubt such a figure is honestly produced, albeit dependent on a featherlight foot on the accelerator, well-inflated tires, etc. Real everyday driving is different, and thus the resultant performance/fuel consumption will be different.

Learn More

See the full range offered by Cavity Trays Ltd. For more see the The Book of Wise Decisions and our Technical Manual Protecting the Building Envelope containing technical data and helpful guidance. Both are available in hardcopy form, without charge upon request. Alternatively, visit our resources page for more.

Remember, whilst standard products are suitable for most applications, some projects require bespoke solutions. Cavity Trays is able to manufacture custom ventilation solutions tailored to specific project needs. Unique architectural designs, historic building renovations, or new builds with unconventional roof structures. Contact Cavity Trays Ltd

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