Acoustic, smoke & fire containment systems

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Fire, Smoke and Weather Sealing for Door Assemblies

Do I need to fit a threshold seal - and if so, why?

BS9999 (an Approved Document to the Building Regulations for England & Wales) states that if a fire rated door has a gap of over 3mm at the threshold, then you do need to fit a threshold seal. It's very difficult to know before the door is installed whether the gap will be over or under 3mm, so we do always recommend fitting a threshold seal. There are other reasons for this too. It is often assumed that the threshold is a low-risk area, but extensive research has proven that this is definitely not the case - an unsealed threshold presents a major cold smoke hazard. That is why undercutting the threshold of a door leaf to provide extra ventilation is extremely risky too, both in practice and principle. Threshold sealing is also essential for acoustic containment, as an acoustic sealing system will only truly be effective if it incorporates every gap around the door, and that includes the threshold. For more information on our threshold seals, please refer to our door bottom seals or drop seals.

Please download our door sealing guide for further information.