They must be installed to close the edges of cavities, including around window and door openings, at the top of the wall, and at junctions where the wall meets a floor or ceiling. This compartmentalises the void to restrict the invisible spread of fire and smoke.
Essential Fire Stops and Cavity Barriers
Cavity barriers are essential building components designed to close concealed spaces within cavity walls, preventing the hidden spread of smoke and flame throughout a structure. These barriers restrict fire movement by creating a tight seal between the inner and outer leaves of a masonry or timber frame wall. They are typically placed around openings such as windows and doors, as well as at the top of wall cavities and floor junctions. During installation, integrating these barriers alongside standard cavity wall insulation ensures that the thermal efficiency of the building is maintained while simultaneously meeting strict fire safety regulations. Each product is supplied 10mm thicker than the cavity width, allowing it to be squeezed into place to form a robust friction fit.
When fitting these barriers within structural voids, they function as a continuous fire stop that compartmentalises the building. The products are usually made from high-density rock mineral wool enclosed in a polythene sleeve, which provides moisture resistance and helps maintain the integrity of the seal. They are available in various sizes to accommodate standard cavity widths, and they must comply with Building Regulations Part B regarding fire safety. For a complete installation, it is common to use appropriate insulation fixings to secure the barriers firmly against the inner leaf, especially in wider cavities or where a friction fit alone is insufficient to support the weight of the material over time.
Fitting a cavity barrier is a straightforward process that requires minimal specialist tools. The flexible nature of the mineral wool allows it to easily accommodate slight variations in the cavity width or irregularities in the brickwork. This versatility ensures a reliable fit around complex junctions and corners. Installing these barriers helps projects comply with mandatory building safety standards by providing a certified period of fire resistance, often up to 60 minutes. When closing off the top of a cavity, these products work effectively alongside the structural elements supporting the roof, and ensuring the correct placement here also supports the performance of loft insulation installed in the attic space directly above.
Cavity Barrier FAQ's
The barrier is supplied slightly wider than the void it is designed to fill. You squeeze the material flat, push it into the opening, and allow it to expand. This creates a secure friction fit against both the inner and outer leaves of the masonry.
You only need a sharp insulation saw or a heavy duty craft knife to cut the material to length. It is important to cut the barrier accurately so that the ends butt tightly together without leaving any gaps for smoke to pass through.
While their primary function is fire safety, most of these products are wrapped in a polythene sleeve that provides a degree of weather resistance. This outer sleeve helps to stop moisture from crossing the cavity and reaching the inner wall.
The product must be 10mm wider than the actual width of your cavity. For example, if the gap between your brickwork and blockwork is 50mm, you need to use a 60mm wide barrier to ensure a tight friction fit that will not sag over time.