Fire door gaps that are too big — tolerances and remedies

Why the gap matters more than it looks

A fire door works as a set: leaf, frame, seals and hardware. The intumescent seal expands to close the perimeter gap once heat builds, but before that point smoke moves freely through anything oversized. Since smoke inhalation is the dominant cause of harm in escape routes, an oversized gap undermines the door's purpose long before the timber is under any real strain.

What causes gaps to open up

In occupied buildings the cause is rarely the original specification:

• Hinges dropping under load, especially where a closer is fitted and only two hinges were used.
• Frames moving as a building settles or after adjacent works.
• Floor coverings replaced with a thinner finish, opening up the threshold.
• A leaf trimmed on site to fix a binding problem.
• Repeated slamming loosening the frame fixings.

Repair options in order of cost

Not every oversized gap means a new door set. Adjusting or replacing hinges, re-fixing or packing the frame correctly, fitting a compliant threshold seal, or adding an approved gap-filling system can bring a door back into tolerance. Where the leaf has been trimmed beyond the manufacturer's allowance or the certification label is missing, replacement is the honest answer and we will say so.

Getting it recorded properly

Each door we inspect is recorded with its location, its measured gaps, its condition and a photograph. That schedule is what you hand to an inspecting officer, and it is what lets you budget remedial work over a sensible period instead of all at once.