Linear Seal in Fire Door Assemblies and BS 8214 Compliance

Definition of Linear Seal

The linear seal is the protected gap between the back of the door frame and the surrounding structural opening into which the fire door assembly is installed. This area plays a critical role in maintaining the overall fire performance of the assembly.

Fire Door Inspections

Fire door inspections are typically undertaken on a non-intrusive basis, relying on visual assessment alongside photographic and documentary evidence to determine the specification and condition of the linear seal.

Where the available evidence is insufficient, an intrusive inspection may be required. This generally involves the careful removal and reinstatement of architraves and should only be carried out by a suitably qualified contractor with appropriate insurance.

Regulation 38 Information

In accordance with Regulation 38 of the Building Regulations, fire door assemblies should be supported by comprehensive handover information. This should include clear evidence of the linear seal, ideally supported by photographs taken before, during and after installation, demonstrating that the installation aligns with the relevant standard.

BS 8214 – Installation Standards (2016 vs 2026)

BS 8214 provides guidance for the specification, installation and maintenance of timber-based fire door assemblies.

Fire door assemblies installed prior to April 2026 may demonstrate compliance with BS 8214: 2016

Fire door assemblies installed from April 2026 onwards should target compliance with BS 8214: 2026

The updated 2026 edition is expected to further reinforce good practice around installation, inspection and documentation, including the treatment of linear seals.

Section 9.4.1 of BS 8214: 2016 (and equivalent provisions in the 2026 edition) specifically addresses the sealing of the gap between the frame and surrounding structure, recommending suitable tested solutions.

Sealants and Linear Seal Performance

Sealants used to form the linear seal, including mastics and expanding foams, should be supported by appropriate fire test evidence.
 

Typically, this includes testing in accordance with:

BS 476-20 or BS EN 1366-4

BS EN 1366-4 assesses the ability of a product to maintain the integrity of a linear gap under fire conditions, including rapid temperature rise associated with flashover.
 

Use of such products is conditional upon evidence of suitability for the specific wall construction and gap configuration in which they are installed. Generic use without supporting test evidence is not considered compliant.
 

Alternatively, sealants may be deemed acceptable where they form part of a successfully tested fire door assembly, in accordance with: BS 476-22 or BS EN 1634-1

Cold Smoke Performance

Where smoke control is required (e.g. FD30S / FD60S and E30S / E60S doors), the fire door assembly — including seals — should also be capable of restricting the passage of cold smoke.
 

Linear seals and associated components should therefore be able to demonstrate compliance with:

BS 476-31.1 and/or BS EN 1634-3
 

Summary

Compliance with BS 8214 remains fundamental to the correct installation of fire door assemblies, particularly in relation to the linear seal. As industry standards evolve, it is important that installations are aligned with the appropriate edition of the standard in force at the time of installation.
 

Equally important is the availability of robust test evidence and installation records, ensuring that both fire resistance and smoke control performance can be verified. Proper documentation of the linear seal is essential in demonstrating compliance and supporting the ongoing fire safety strategy of the building.