What is the recommended gap between leaf edge and frame for a fire rated door?
The recommended leaf edge to frame gap specified in BS 8214: 1990 is 4mm on all edges. Intumescent seals are engineered to react within this size of gap to give optimum sealing and clamping performance.
It is through extensive testing of fire rated doorsets, together with knowledge of the pressure regime within a fire test, that a larger gap is permitted at the threshold of the door. There is negative pressure at the threshold during test conditions and so cool air is drawn in underneath the door. It is for this reason that there is unlikely to be a failure at the threshold and also why there is no need to fit a perimeter intumescent strip at this location (doorsets below FD60 performance). A larger gap at the threshold is also useful from a practical end use application for accommodating floor coverings. We recommend a gap of 10mm from the bottom of the leaf to the structural surround.
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