Cavity barriers are defined as a construction, other than a smoke curtain, provided to close a concealed space, such as in a roof or ceiling void, against penetration of smoke or flame, or provided to restrict the movement of smoke or flame within such a space.

Cavity barriers require special attention from the designer. By their very nature they are often hidden once installed and are therefore difficult to inspect after installation, handover and subsequently through the life of the building. However the barrier will not become effective until it has been covered up and later inspection, by re-opening the work, could affect its integrity.

The designer should indicate where there is a need for a cavity barrier. Because it is an important element that is often accidentally missed out during construction, the responsibility for its installation and performance must be clearly identified. This is all the more important as the cavity barrier may well be hidden after its installation.

Unless clearly defined, it is possible for an in-appropriate sub-contractor to be given the task of installing cavity barriers.

The requirements and responsibilities for the provision of cavity barriers must be clearly stated in the contract(s). Proprietary systems must be designed in accordance with manufacturer’s instructions.

Recommendations on the provision of cavity barriers are given in Approved Document B and its equivalent Scotland/Northern Ireland guidance. Co-ordination between different trades and contractors is essential particularly when aligning or joining one cavity barrier system with another.

The insulation and integrity requirements may be different from those required by the compartment walls and floors of the building. Care should be taken therefore with their use, particularly for large barriers. It should be noted that barriers in a roof space for example, which are located above the fire separating divisions must provide the same level of insulation and integrity as the division. The recommended
positioning and spacing of Cavity Barriers is given in regulatory guidance documents.

The successful installation and maintenance of cavity barriers is dependent on the supports, top fixing, edge fixing and jointing systems. Cavity barriers are usually tested in fire conditions for a maximum of 3 m vertical drops. Higher drops are viable provided the barrier and support/fixing systems can accept the higher load of the extended drop. In many cases this may require additional support elements and manufacturers can provide the necessary detail. Some will offer site advice free of charge. Unless clearly defined, it is possible for an in-appropriate sub-contractor to be given the task of installing cavity barriers.