Gaps around a fire door, and why millimetres matter

Fire Doors Brisbane — firedoorsbrisbane.com.au — arranges these inspections with a QBCC-licensed contractor across Brisbane, Ipswich, Logan, Redlands and the Gold Coast.

Published 10 November 2026

Why gaps matter so much

In a fire, flame and hot gas look for the easiest way through. A solid leaf holds them back; the gap around it does not.

A doorset is tested with specific clearances at the head, the jambs, the meeting edges of double doors and the threshold. The rating only holds while those clearances do.

Where the limits come from

The allowed gaps come from the doorset's tested configuration under AS 1905.1 and the evidence for that door. They are not a general rule of thumb, and they can differ between door types.

That is why the inspector measures them against the door's own requirements rather than eyeballing them.

Why gaps open up

Buildings move. Hinges wear and drop the leaf. Frames are knocked by trolleys and furniture. Timber leaves swell and shrink with Brisbane's humidity. Floor coverings are changed, raising or lowering the threshold.

Most gaps did not start out wrong. They drifted.

The fixes that are not fixes

Planing a leaf to stop it binding, then leaving a gap at the head. Packing a frame with whatever is to hand. Adding a thicker seal to hide a gap the seal was not designed for.

Each can leave a door that closes nicely and is no longer within its tested configuration.

What a proper fix looks like

Adjust or replace the hinges, re-hang the leaf, repair the frame, or deal with the threshold, using components the doorset allows. Then re-measure and record the result.

Sometimes the honest answer is that the leaf has moved too far and needs replacing. The contractor should say which, and why.

What you can check yourself

Close the door and look for daylight around it from the dark side. Check that the seals touch the leaf all the way round. Watch whether the door drags, bounces or has to be pushed to latch. None of this replaces the inspection, but it tells you which doors to mention.

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