To understand what a cavity barrier is, we must first define what we mean by a ‘cavity.’ In a home a cavity is an enclosed space usually found within a wall or enclosed by structural beams that serves no practical purpose. In an external wall a cavity can potentially function like a chimney facilitating the movement of flames, gases and smoke to other parts of the building. With cavities now understood it is important to have a clear definition of a cavity barrier.

Cavity barriers defined

A cavity barrier, which is sometimes referred to as a stop sock represents a block made of fire-resistant material that seals off the kinds of cavities we mentioned in order to restrict the spread of fire.

Why is it important to discuss fire cavity barriers?

Cavity barriers are now considered mandatory as a fire protection element in the construction of new homes. It is the responsibility of the builder to ensure that cavity barriers are installed. A recently undertaken review and report concluded that many UK homes have been built without adequate fire protection. This report was in the aftermath of the Grenfell disaster and was led by Atkin Chambers. It found that there are missing or poorly fitted cavity barriers in many timber-framed properties. In addition to this, of course, older properties would have been constructed prior to the time when cavity barriers were considered mandatory and as such a fire risk assessment should be carried out on such properties by an accredited company.

Where are cavity barriers fitted?

The relevant guidelines are covered in BS 9991 (fire safety in the design, management and use of residential buildings) and ADBV2 (fire risk assessment strategy) and form part of building regulations. The latter dictates that cavity barriers should be fitted:

• At the junction situated between an external cavity wall (except when walls have two leaves of masonry or concrete with a minimum thickness of 75mm) and each compartment floor and compartment wall.
• At the junction between an internal cavity wall (except when walls have two leaves of masonry or concrete with a minimum thickness of 75mm) and every compartment floor, compartment wall, or other wall or door assembly which forms a fire-resisting barrier.

How fire cavity barriers provide protection

The mechanism of a cavity barrier is achieved by the sealing off of gaps within a cavity during fires. Fire cavity barriers are made of highly heat sensitive materials and when a fire starts they will expand to seal off the gap. By slowing down the spread of a fire it allows any inhabitants more time to evacuate and will also give firefighters more time to put the fire out, potentially reducing the damage done to the property. Those cavities that have not been effectively managed will facilitate the drawing in of air and smoke, allowing the fire to spread much more quickly. It seems such a simple solution to what can be a devastating problem, so there is no excuse for not fitting fire cavity barriers in new homes.