How do you fix fire door gaps?
To fix fire door gaps, first find the cause. A dropped door usually needs hinges tightened or replaced and the leaf re-hung. Worn seals are replaced, and a bottom gap is closed with a drop seal. Uneven gaps along the frame mean the frame has moved and needs re-setting, not planing the leaf.
By Sebastian Grabowski, DC Fire & Security, Luton. Updated November 2026.
Start with the cause, not the gap
Government guidance says the gap between door and frame should not be more than 4mm, and the gap at the bottom as small as practicable without the door snagging on the floor. A wide gap is a symptom. If you fix only the number you can leave the fault in place and the gap will open again. Our page on fire door gap tolerances has the measurements, and a gap gauge is the right tool for taking them.
Close the door and look at the pattern of the gaps. The pattern usually tells you what has happened.
| What you see | Likely cause | Usual fix |
|---|---|---|
| Wide gap at the latch side top corner, tight at the bottom | Hinges loose or worn, door has dropped | Tighten or replace hinge screws and hinges, re-hang the leaf |
| Gap grows from top to bottom or the other way | Leaf has twisted or warped | Re-hang if slight, a new leaf if not |
| Gap uneven down the length of the frame | Frame has moved or was fitted out of true | Re-set the frame |
| Gap at the bottom too big | Floor finish has changed, or door cut too short | Fit a drop seal or a threshold where suitable |
| Gap fine but the seal does not touch | Seal worn, painted over or missing | Replace the seal |
| Gap too small and the door binds | Paint build up, swollen leaf or hinge screws pulled | Ease carefully within the manufacturer's limits, check the hinges |
Repairs, in order of how far they go
Hinges. Look first for loose or missing screws, and replace them with the right ones. A hinge that has pulled out of soft timber may need the fixing repaired. Fire doors need hinges that suit the door, so a failed hinge is replaced with a matching rated one. Our guide on fire door hinge requirements explains the spec.
Seals. Intumescent strips and smoke seals only work if they are undamaged, touch the door or frame and are not painted over. Worn seals are replaced to suit the door. See intumescent strips and smoke seals.
Bottom gap. A drop seal closes a gap under the door when it shuts. A threshold seal is another option where the floor allows. Check the door's test evidence first.
Re-hanging. Where the leaf has dropped, the leaf is lifted back into position, the hinges are reset and the closer is re-adjusted so the door shuts into the latch.
Frame re-setting. If the gaps are uneven all the way down the frame, it is the frame that has moved, and no hinge adjustment will cure that. The frame has to be re-set or replaced. This is the repair people most often skip, and the gaps come back within months.
New leaf. Where the leaf is warped, split or cut down too far, a new leaf in the existing frame is the answer. That is an option when the frame is sound. See repair or replace.
What not to do
Do not fill a gap with expanding foam, decorator's caulk or wood filler. They are not fire rated, they hide the defect and they can stop the door closing. Do not plane a lot off the leaf either. Taking too much off the edge can remove the intumescent strip or push the door outside the limits of its test evidence. A small, careful trim is sometimes within the manufacturer's allowance, and if you are not sure, do not cut.
Do not fit bigger seals to cover a large gap. A seal works within the range it was tested for, and a gap well over 4mm needs the cause fixing.
Who should do the repair
Government guidance says repairs or replacement should be done by a competent contractor as soon as reasonably practicable. A simple missing screw can be sorted by the building's maintenance person, but anything that changes the door, the frame or the seals needs someone who knows fire doors. Our crew repairs fire doors and gives fixed prices after seeing the inspection report or photos. Our fire door repairs page explains how to start.
Frequently Asked Questions
Can I fix a fire door gap myself?
Is a 5mm gap on a fire door a fail?
Can I use intumescent filler or foam in the gap?
Can you plane a fire door to close a gap?
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Email your report or photos to info@dcsecurity.co.uk, or use the form. We usually come back with a fixed price the same day. Luton, Bedfordshire, Hertfordshire, Buckinghamshire and London.
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