What gap under fire door

[Guest Field]

When renovating a 3 storey house and putting in fire doors can a gap be left at the bottom of the door to allow for floor coverings to be added as I do not want to decide whether to have carpet or Karndean type flooring. I have been told that carpet or whatever has to be installed for the doors to pass Building Regs!

[Neil Ashdown MAFDI]

The gap at the bottom of the fire door is important. If the gap is too large, the issue is 1) That cold-smoke may spread from the fire side and 2) That cold air from the non fire side may be drawn under the door and feed the fire to aid its development.

The maximum gap allowed for a fire door is generally 10mm between the door bottom edge and the floor covering. The maximum gap for a fire door with smoke protection is 3mm but if this is not possible a gap of up to 10mm is permissible with the use of a smoke seal to seal the gap at the door bottom edge.

The easiest way to achieve the above is to use a hardwood threshold strip, that way you can get a consistent gap as well as avoid the door sticking on the carpet and failing to self-close.

[Tom Sutton]

The fire safety issue is that the gaps specified by Neil has to be there when the work is completed and the floor coverings are fitted. As for the Building Control Office/Authorised Inspector, issuing a completion certificate, you will have to speak to them.

[Guest Novice]

The gap under fire doors is becoming a bigger problem as we move to new buildings with underfloor heating in the floor screed. To reduce costs and increase profits contractors are reducing the depth of the finishing screed and in a recent inspection I found gaps of up to 32mm between the bottom of a fire door and the finished floor covering!

[Tom Sutton]

It is very frustrating but it is a problem that has to be resolved check out http://www.safelincs.co.uk/blog/2013/08/09/gaps-underneath-fire-doors/.

[Guest Novice]

Thank you for the link Tom

[Guest Kay]

Please can I ask guidance on the following. I am a tenant in a housing association flat. There is a 1 inch gap (highest point) under my front external fire door and no fire strip. I moved into the property in May 2018. Following the joiner attending 2 weeks ago after me advising the association of there being no fire strip and the gap underneath, over 4 weeks ago, the housing association have told me I am getting a full upgrade. I asked what this meant and was told they are putting a letter plate on/adding hinges/A drop seal and cold smoke seals. I am worried about the gap under the door and they have said it will confirm to standards required for a fire door. Please can anyone with this kind of knowledge advise me? 

 

[Tom Sutton]

It depends on what is meant by drop seal, if it is drop down smoke seal that should solve the problem. Check out https://www.safelincs.co.uk/surface-mounted-drop-down-smoke-seal/.  

[Neil Ashdown MAFDI]

Maximum gap under a timber based fire door should be 8mm to 10mm. If the gap is more than that then a threshold plate is required to reduce the gap to 10mm or below. Where the door is required to restrict spread of cold smoke (which will be the case with a flat entrance door) the maximum gap should be 3mm. Where the 3mm max gap cannot be achieved a threshold smoke seal should be fitted.

Therefore the upgrading contractor should reduce the gap to 10mm before fitting a threshold smoke seal. 

[Tom Sutton]

Neil assuming the floor is not level and you if you fit a threshold plate to the floor would this not create a tripping hazard or could you make a bespoke one out of hardwood with a chamfer on each side?

[Neil Ashdown MAFDI]

Hi Tom,

Clearly, using hardwood for the threshold plate allows you to 'plane-in' to achieve a better degree of gap accuracy. Other aluminium threshold plates are available and compliant to Part M Access Regulations.

It is advisable to risk assess TRIP hazard vs SMOKE hazard before fitting a threshold plate to the floor.

[Guest Dawn]

Hi can anyone help on a related topic please. We recently moved into a 3 storey town house with integral garage, circa 1985. The internal garage door doesnt have any intumescent strips around it. The gap under the door is about 20mm. Should there be strips? There is a groove in the door frame. How can I draught proof the door at the bottom. The hall floor is laminate, the garage door opens into the garage? I think its a fire door as it is thicker than a normal door and hung on 3 hinges.

Thanks for your help

[Neil ashdown]

For the door to be properly effective as a fire door the maximum gap at the bottom should be 10mm.  You could fit a threshold plate to the floor or cill under the door to rectify this or if you prefer you could fix a hardwood lipping to the bottom edge of the door.

Today's building regulations require such a door to be self-closing and to restrict spread of cold smoke FD30(s) so a suitable self-closing device, the correct size intumescent seals and smoke seals should be fitted.  To seal the gap at the bottom edge of the door you could fit a threshold seal (see below). Not sure what the requirements were in 1985.

[Guest Russell Evans]

A question RE threshold strips (ally) in reference to door leaf thickness. If an ally thresholds strip is permissible in relation to Part M regs and the gap under a fire door needs only increasing by circa 5mm to make it to 10mm (bearing in mind the door also has a retro fitted dropseal to achieve a gap of 3mm or less for smoke rating). Does the threshold strip need to be the equivalent to door thickness 44mm leaf  = 40mm strip (commonly available on the market) 54mm doors a 60mm strip (commonly available on the market) or, can a 40mm strip be used in both scenarios?  After a lot of searching I can only find information for under door gaps relevant to oxygen feeding the fire and not a clear definitive answer on the gap height in relation to the thickness. I'm also wondering if the strip needs be used primarily on the fire side face of door or, it needs to positioned in the centre?  

[Neil ashdown]

The floor mounted threshold plate should be at least as wide as the thickness of the door leaf.

The threshold smoke seal should seal the gap along the entire length with a light even contact but not exhibit too much force and cause difficulty with the door self-closing action. If it is impractical to fit a threshold seal, the gap should not exceed 3mm at any point. For fire doors that are not required to restrict the spread of smoke the threshold gap should generally be 10mm maximum or whatever is required by the particular door manufacturer.

[Guest Tommy S]

Hi all, 

Regards to minimum gap to underside of door, understood 10mm for Fire and 3mm for Smoke. In instances where there is a gap of 11mm+ and the requirement is Fire and Smoke, assume this would require either lipping and a drop seal, or threshold/drop seal? One of those combos. It is my understanding that a drop seal cannot be used to bring a door under the 10mm tolerance for fire purposes? 

[Tom Sutton]

I am not aware of any such ruling, if you can get a drop down seal that will function correctly then I would use it irspective of the size of gap.

[Neil ashdown]

A drop-seal will not resolve the issue of the door being non-compliant in terms of the 10mm gap for fire resistance purposes.  

[Guest Phoebe]

Hi there,

I have an excessive gap at the bottom of my fire door. This is due to uneven floors in an old house- when the door is open the door is flush to the floor, but when the door is closed there is a gap underneath (greater at the opening). Fitting new fire doors would therefore not solve the problem. I have seen talk of threshold seals and drop down door seals. Can you advise if these need to be certified or made of specific materials, and whether they would work with slanted gaps? Many thanks 

[Guest John]

Hello, I’m in new built property where the floor is not perfectly laid down. This means that the gap between doors and floor sometimes is not the same throughout. The developer claims that the gap must be measured by the hinges and not at the end of the door.
 

I find this explanation very strange as the fire wouldn’t make a difference between various parts of the door.

 

I would really appreciate some advice on how to deal with this.

 

Thank you so much,

John

[Guest Phoebe]

On 13/06/2022 at 11:56, Neil ashdown said:

A drop-seal will not resolve the issue of the door being non-compliant in terms of the 10mm gap for fire resistance purposes.  

If a drop seal does not make the door compliant, then what is the purpose/point in having a drop seal? I cannot achieve a gap < 10mm with a door due to unlevel floors in an old house (door has to be cut short at bottom to allow full opening). Does this mean there is nothing I can do to be compliant? I was hoping to use threshold plates + drop down seals to reduce gap, is there point in me spending the money if I can’t get doors certified anyway? Thank you 

[Neil ashdown]

Hi Phoebe,  For fire resistance purposes the max gap is generally 10mm, so you could fit a threshold plate to the floor to reduce the gap and then fit a flexible seal to address the cold-smoke spread issue.  BS 8214: 2016 sections 9.5.3 and 12.3 refer.

[Guest Guest Graham]

If I have a 10mm plus gap at the bottom of a door could I not fit an aluminium kick plate of say 2mm thick to reduce the gap?

[Neil ashdown]

In terms of compliance with the British Standard, that would not be a suitable solution.  If it's a new fire door leaf refer to the data sheet for details and if its an existing fire door fitting a threshold plate to the floor may be the easiest way to resolve the problem. 

[Guest Keith W]

Hi. Some great posts here and some great info. I have a new build. It is a 3-story town house. Our snagging found a few fire doors that have lower gaps more than 10mm (top and sides are fine).

Some can be resolved using a threshold bar. For some others this is not practical. The aim here is fire resistance, not smoke resistance. Is it possible to use a surface mount brush seal on the base of the door which will greatly reduce the gap and bring it nearer to 5mm ? 

Also, am I right that the magic 10mm is driven by the ventilation requirements given in approved document f of the building regs.

The government site on fire door gaps (6.7.g) simply states "the industry standard is that the gap size should never be more than 4mm, except at the bottom of the door, where the gap should be as small as practicable, while ensuring that the door is unlikely to snag on the floor even if the door drops slightly on the hinges."

Thanks for any input. Keith