Hi, I have to install a batwing smoke seal to a FD120 timber doorset and wanted to know if there is a specific size I have to use? I wanted to use the 10x10mm seals as this would mean I wouldn’t have to move the door stop back as much as the bigger seals. Is 10x10mm acceptable? I’m unable to find any information that tells me 10mm cannot be used.

The purpose of a smoke seal is to restrict the spread of cold smoke. The dimensions of the seal is not related to the fire rating of the door. Refer to Building Regulations Approved Document B, Appendix C 'Fire Doors' for the requirements.

See Table C1 and Notes 2

There is also useful information about smoke seals at https://www.ifsa.org.uk/