Threshold Sealing in BS 8214:2026

One area where the revised standard provides greater clarity is the treatment of threshold gaps and the use of bottom‑of‑door sealing systems. This article summarises the relevant changes and outlines how threshold sealing should now be considered as part of a compliant fire‑door system.

1. Removal of former acceptance of unsealed thresholds

Earlier practice allowed smoke‑control doors to be assessed or treated as compliant when the threshold was left unsealed. BS 8214:2026 now makes clear that this is no longer appropriate.

“While in the past it has been deemed acceptable to allow smoke control doors to be unsealed at the threshold… this is no longer the case.”
“…the smoke leakage performance is required to be measured over the whole specimen, including the threshold…” 

This change means that any door intended to restrict the movement of ambient‑temperature smoke must incorporate threshold sealing that forms part of the tested or classified performance.

2. Thresholds treated as part of the full smoke control perimeter

BS 8214:2026 confirms that the bottom of the door must be addressed in the same way as the head and jambs when smoke control performance is required. Where smoke sealing is needed:

• The gap beneath the door must be sealed using a suitable bottom of door sealing system, for example a drop seal.
• The sealing system should provide a leakage rate not exceeding 3 m³/h per metre at 25 Pa, tested in accordance with BS 476-31.1 or BS EN 1634-3.

This ensures the threshold contributes to the overall smoke control performance of the door assembly.

3. Considerations during specification and installation

The updated guidance also recognises practical factors that influence threshold performance. These include:

Floor flatness and floor finishes
The actual achievable threshold clearance can be affected by surface levels and the degree of flatness across the door’s opening arc. These conditions are external to the door manufacturer and may only be fully understood at the point of installation.

Environmental and operational conditions
There are situations where the operation of the door or the function of the sealing system may be influenced by building conditions, such as pressure differentials. This may need to be considered when selecting or configuring threshold sealing.

Specific application areas
Healthcare and other hygiene sensitive environments may require additional considerations regarding materials and cleaning processes, as noted in the updated guidance. 

4. Fire doors as part of a complete system

BS 8214:2026 moves further toward treating fire resisting and smoke control doors as coordinated systems rather than individual components. This includes:

• Door leaf
• Frame
• Seals (including threshold sealing)
• Ironmongery
• Interfaces with surrounding construction

Threshold sealing should therefore be selected as part of the overall system and aligned with supporting test evidence.

5. Alignment with wider smoke control strategies

Threshold sealing forms one element of a broader smoke control approach within a building. BS 8214:2026 highlights the need to consider the interaction between door seals and building wide smoke control measures (e.g., evacuation strategies, ventilation, and pressurisation). Ensuring compatibility between the door’s threshold seal and the building’s wider smoke control measures supports consistent performance.