Cavity Barrier Installation Best Practices

Cavity barriers must be installed to the tested configuration for the specific product, substrate and cavity width, with fixings, compression levels and orientation matching the test evidence. Incorrect installation can invalidate that evidence and compromise fire performance.

Approved Document B sets out where barriers must be positioned: at compartment floor lines, compartment wall junctions, and the edges of cavities around openings (Volume 2, Section 9, Clauses 9.2 and 9.3 for non-dwellings; Volume 1, Section 9, Clauses 9.10 and 9.11 for dwellings).

In ventilated façade systems, open state barriers such as the VFB 60/60, VFB 120/120 and VFB Plus must maintain the required air gap while still achieving a reliable fire seal when activated. Over-compression is one of the most common installation errors, and it can compromise both airflow and fire performance.

For product-specific fixing schedules and tested configurations, visit the Tenmat Technical Hub.

Cavity barriers can go in at new build stage, as part of the planned build sequence before façades are closed, or be retrofitted into existing buildings where fire risk assessments, façade inspections or external wall surveys identify missing, damaged or non-compliant barriers. New build is the more straightforward scenario, as access to the cavity is unrestricted and the substrate and cavity width are known in advance.

Retrofit is more complex, since barriers often need to go into concealed cavities behind finished façades with limited access. Under the Building Safety Act 2022, accountable persons for higher-risk buildings are legally obliged to act on identified deficiencies. In occupied buildings, installation needs careful sequencing to minimise disruption, and phased programmes are common on larger residential blocks where the whole façade can’t be accessed at once.

In every case, installation must follow the tested configuration for the chosen product and align with the project fire strategy.

Who carries out the work depends on the project type. In new build, it’s typically the main contractor or a specialist façade subcontractor, as part of the planned build sequence. In retrofit and remediation projects, specialist passive fire protection contractors are more commonly engaged, particularly where intrusive works are needed to access concealed cavities.

Whoever installs them, they must follow the manufacturer’s product-specific guidance, since cavity barriers are tested in specific configurations and any deviation, whether in substrate, fixing method, compression or orientation, can invalidate the product’s fire performance.

NHBC and LABC both require evidence of correct installation as part of their warranty and building control processes for new residential construction. Retaining installation records and product documentation supports compliance and contributes to the golden thread of building information required under the Building Safety Act 2022.

For product-specific installation guidance, refer to the Tenmat Technical Hub.

NHBC requires cavity barriers in new residential construction to be installed in accordance with Approved Document B and BS 9991, correctly positioned at compartment floor lines, compartment wall junctions and around window and door openings, and within the maximum cavity dimension limits set out in both documents.

NHBC inspectors assess installation as part of the building control and warranty process. Products must be installed to the manufacturer’s guidance and supported by test evidence to BS EN 1366-4, with classification to BS EN 13501-2. Where installation doesn’t meet the required standard, remediation is needed before the warranty is issued.

LABC has a similar requirement for compliant installation as part of its building control sign-off. Retaining data sheets, installation records and test certificates supports sign-off with both bodies and forms part of the golden thread of building information required under the Building Safety Act 2022.