Gaps Underneath Fire Doors

We are often asked questions in our Fire Safety Forum about gaps underneath fire doors. Are they allowed and if so, how big can they be? Here we outline the current regulations and solutions.

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. But, if the gap is too wide, it will compromise the door’s effectiveness in preventing fire and smoke from escaping into surrounding areas. The door may not provide the protection that it should if a fire breaks out.

Are gaps allowed under fire doors?

The general advice for fire doors is that a gap of up to 10mm (according to Building Regulation Approved Document F) is permissible underneath the door. This allows for adequate ventilation without compromising the performance of the fire door. If you can, check with your fire door manufacturer as they will be able to give you specific advice for your circumstance (as recommended in the BS 8214:2016 – 9.5.3). If smoke protection is required by Building Regulations, the maximum gap underneath the fire door is reduced to 3mm.

How can I make the gap under my fire door smaller?

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?

If you would like further advice about your fire doors, read our Fire Door FAQs or fire door guide. Alternatively, our knowledgeable fire door team will be happy to advise. They can be contacted on 01507 462 176 or email