Hi, is it ok to rout a fire door to fit a smoke and fire seal, or does that affect the fire resistance ?

Thanks

It is acceptable to router a groove in the top and vertical edges of the timber-based fire door leaf or leaves. The groove should be central to the leaf thickness except at the meeting edges of double door leaves where two offset seals may be a requirement. Do not fit a seal to a slave leaf that has flush bolts at its meeting edge, fit the seal to the main leaf instead.

The groove must be only just large enough to accept the seals as a tight fit.  Take care to make sure the groove is only just deep enough to suit the seal thickness as the seal must be flush with the door leaf edge. 

If you can find a BWF Certifire label (see below) on the door leaf you can refer to the CF certification data sheet for details about the type, configuration and size of seals required. If the groove will damage the BWF Certifire label, carefully remove it and reposition it alongside the groove.