Gaps Underneath Fire Doors

What is the maximum gap allowed under a fire door?

The maximum gap allowed under a fire door is usually 10mm. However, this is not always the case. It is essential to consult the manufacturer’s guidance for the specific type of door that has been installed.

Why should I worry about the gap under my fire door?

Fire doors need a bit of a gap around them to swing freely above the floor covering. However, if the gap is too wide, the fire door’s effectiveness will be compromised. In that case, the door may not provide the protection that it should if a fire breaks out.

All Responsible Persons for fire safety have a legal obligation to maintain their fire doors in accordance with its certification. There is new legislation for the maintenance of fire doors in residential flats. As a result of this legislation, thorough fire door checks must be caried out every three months in properties over 11 meters high, or containing two or more separate dwellings. Consequently, if fire doors are found to be non-compliant, and there are no plans in place for repair or replacement, the Responsible Person could be prosecuted.

Are gaps allowed under fire doors?

Yes, fire doors should have gaps underneath them to allow free movement and ventilation. The allowance for the size of this gap varies between manufactures and must fall within the specified range for that door. Therefore, as recommended in BS 8214:2016 – 9.5.3, you should check requirements with your fire door manufacturer. This is the only way to ensure that every door on your premises is complaint. The door manufacturer should be able to give you specific advice for your circumstance.

If smoke protection is required by Building Regulations, the maximum gap underneath the fire door is reduced to 3mm.

How to fix fire door gaps

Surface mounted drop-down smoke seals or rebated drop-down smoke seals can be fitted to existing fire doors if the gap is too large. Usually suitable for gaps of up to 14mm, they can be attached to the bottom of the door. When the door closes, a plunger makes contact with the door frame and lowers the seal to the floor, closing the gap under the door.

Surface Mounted Drop-Down Smoke Seal

Need further advice?

Gaps underneath fire doors aren’t the only place where compliance issues can arise. To carry out a full fire door check, why not use our free fire door inspection checklist? If you find that your door is unsuitable and needs to be replaced, you can view our range of standard and bespoke fire doors, or contact our friendly and knowledgeable fire door team at 0800 433 4289 or email

If you would like further advice or information about your fire doors, read our Fire Door FAQs or fire door guide.