What clearance is allowable between a fire door and a frame for a fire rated door?
The preferred door edge to frame clearance specified in BS 8214: 2008 is 4mm on all edges.
This 4mm clearance is required as Intumescent seals are engineered to react within this clearance size to give the optimum sealing and clamping performance.
It is only with extensive testing of fire rated doors and doorsets, combined with knowledge of the pressures within a fire test, that larger clerances are allowable at the threshold of the door where it meets the floor.
Tests have shown that there is negative pressure at the threshold during test conditions which allows cold air to be drawn in underneath the door, on this basis there is unlikely to be any failure at the threshold, there is therefore no need to fit a perimeter intumescent strip at this area but this applies only to doorsets below 60 minutes performance.
More clearance at the threshold is useful and practical in as much as there is space for various types of floor covering, having installed doors and frames for many years we would recommend allowing 20mm from the timber floor to the underside of the door if you intend fitting carpets.
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