CAVITY BARRIERS
WHAT IS A CAVITY BARRIER?
A cavity barrier is type of passive fire protection system that prevents the spread of fire by dividing void spaces within ceilings, walls and floors. They work by sealing the gaps in a cavity in the event of a fire. Cavity barriers are designed and installed to prevent smoke and/or flames travelling through concealed spaces and extensive cavities by restricting their pathway with fire stopping materials.
These spaces often serve no function; however, unsealed cavities can allow the spread of fire and essentially act as a chimney as the fire will search for its nearest point of air source, providing an easy route for smoke and flames to move around the building and between compartmentation barriers. Fire can spread very quickly and un-noticed in these areas until it is too late so it is crucial to ensure they are protected adequately.
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Approved Document B of the Building Regulations defines a cavity barrier as a construction, other than a smoke curtain, which:
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​closes a concealed space against penetration of smoke or flame; or
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restricts the movement of smoke or flame within such a space.​​
HOW DOES A CAVITY BARRIER PERFORM?
Cavity barriers are normally formed from mineral fibre and/or intumescent materials, which expand when exposed to high temperatures and in turn closing the void and stopping the spread of smoke and flames from one compartment to another. This increases time for appropriate action to be taken in stopping a fire, evacuating a building successfully, and reducing structural losses in the event of a major fire.
Working very closely with our partners we can ensure the correct cavity barrier is selected and tested for the specific scenario and building makeup. The correct installation of cavity barriers within the building is essential in ensuring compliance with fire safety regulations and building codes.
WHERE ARE CAVITY BARRIERS REQUIRED?
Cavity barriers should be fitted near the edges of internal cavities around openings such as windows, door openings or extract vents, as well as the junctures of each compartment wall, floor, and exterior cavity wall and within roof or floor spaces.
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​​Approved Document B, paragraph 9.3 states cavity barriers must be fitted:
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​at the juncture of each compartment wall, compartment floor and exterior cavity wall (excluding walls with two masonry leaves or concrete with at least 75mm thickness).
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at the juncture of an interior wall (excluding walls with two masonry leaves or concrete with at least 75mm thickness) and each compartment wall, compartment floor, or other door or wall construction that can function as a fire-resisting barrier.​​
According to both BS 9991 and Approved Document B Volume 2, cavity barriers are required to have 30 minimum integrity and 15 minimum insulation (BS 9991 Figure 24 and Table 3). Both documents also allow cavity barriers to provide only 30 minutes’ integrity; clause 19.2 of BS 9991 cites 0.5mm thick steel and 38mm timber as being suitable cavity barrier materials for the perimeter of windows.
Cavity barriers should be designed and fitted according to building regulations. Advice should be sought from a fire engineer and all fire protection systems should be fitted and maintained by a certificated third-party company.
RWS works very closely with leading Cavity barrier manufacturers such as Firefly, Rockwool, ARC and AIM to ensure all our installs are installed to tested and certified details. On the occasions installs are tricky we will arrange a site visit with the relevant manufacturer to look at other options or technical assessments.
