How much can I cut of a fire door?

[Guest NickAr]

I am a mechanical design engineer and was wondering what is the maximum distance a fire door can be undercut by. I have contacted building control and have been informed that this is 4mm, but have been told by other engineers that they have previously been told that it is 20mm. Please could you confirm the actual dimension as i do not seem to be able to find anything with the Building Regulations either.

[Tom Sutton]

The best guidance on fire doors is Architectural and Specialists Door Manufacturers Association the Best Practice Guide to Timber Fire Doors. The guidance on installation is http://www.asdma.com/pdf/installationlflt2.pdf . It depends on what you means by undercut, if it is the lipping on the side of the door that should not exceed 3mm on each side, you cannot touch the top side and the threshold you will have to contact the manufacturer as it depends on the construction of the door. If you are talking about the gaps around the door that is 2mm to 4mm top and sides. The threshold should not exceed 8mm.

Check the British Standard BS 8214:1990 and the above guides.

[Guest ChrisNight]

Building regulation part F calls for doors in New dwellings to be under cut by 10mm above floor finishes and 20mm undercut above the floor boards, to allow air transference

However, some of our doors are fire doors (to protect the means of escape).

Could you please advise what is the maximum permissible gap below a fire door?

[Tom Sutton]

First ADF states 10mm above the finished floor The 20mm above the floorboards is to allow for a carpet to be fitted leaving 10mm above the finished floor. Therefore the gap is 10mm.

The guidance in British Standard BS 8214:1990 Code of practice for Fire door assemblies with non-metallic leaves, states the gaps around the door is 2mm to 4mm top and sides. The threshold should not exceed 8mm. However if the gap is 10mm I am reasonably certain it would be accepted.

[Guest LynneCran]

We have a project where to keep the width of the door for Scottish building Standards a corner of about 40mm had to be cut from an oak veneered 4 panel 30FD door. (to accommodate new stairs) The hard wood lip was replaced and the intumescent strips fitted but the officer is questioning it's integrity. Would the door lose that much integrity (solid block frame) or is there anything we can do to upgrade it?

[Tom Sutton]

Have you modified the frame as well so the door sits in a 12 mm rebate also have you maintained the 2 or 3 mm gap between the door and frame

[Guest Lynnecra]

Hi Tom

Yes the frame has been built on the same angle with all the same rebates/fit and continuous intumescent strips.

Regards

Lynne

[Tom Sutton]

First check out the footnote on my responses.

Nobody can give a definitive answer to you question it is all about informed guessing.

1. One of the most important considerations is how well the fire door set has been installed and meets all the required tolerances.

2. Fire door can fail because it warps and creates a gap between the frame and the door. ( Construction and Hinges)

3. If if the door does warp slightly is there a means of sealing the gap. (intumescent strip)

4. Fire attacks the edge of the door first and high lights any faults. (Hardwood lippings and intumescent strip)

5. If the fire door is modified it loses certification grantee unless conducted by an approved company.

The only way to check these points is by examination and with favourable responses you should be able to make a good case to convince the Building Control Officer or Fire Inspecting Officer the fire door will function as required.

[Guest WasimAhm]

I am a tenant in a HMO, and I am concerned about a Fire Door in the property. The door is undercut by 2/3 inches from its base, and with it being located close to the kitchen, I'm afraid of the great hazard this may pose.

Should this be rectified by the Landlord to comply with health and safety regulations, or is it legal to have the door undercut by that amount?

[Tom Sutton]

It would appear the gap under the door is excessive and it should not exceed more than 8mm/10mm from the level of the finished floor or covering to the underside of the door, providing it is a necessary fire door. Is the door in question protecting an escape route from a high fire risk? I would suggest you contact the local Fire and Rescue Service and ask for their opinion.

[Guest Paulsto]

Hi,

I've had a builder put a Fire Door in my loft conversion, they have put a Howdens DIF4060 in. Only thing is, the Howdens documentation says you should not trim anymore then 5mm of the bottom or top rail but they have trimmed 20-25mm of the bottom rail. Does this mean the integrity of the door has been compromised and so we no longer have a 30 minute fire door?

Many thanks.

Paul.

[Tom Sutton]

According to BS 8214 2008 it states the gap should be in accordance with the manufacturers instructions therefore I would suggest you need to contact the manufacturer for their advice.

[Guest paddy]

Hi, I have a query and am keen to find out if there is any guidance/legislation that actually quotes the 8/10mm undercut limit for fire doors. I install Envirovent PIV systems and require an undercut for them to perform effectively. Building Control require fire door certification for the door but as this is at design stage the type of door has yet to be decided and I dont believe it states the undercut anyway!!! In short I need to establisnif their is definitive guidance around this issue!!

Thanks in advance for any help you can provide!

Paddy

[Tom Sutton]

Fire doors are designated FD or FDs followed by the degree of fire resistance in minutes. Both types of fire door have always required the gaps on each side and the top to be 2/3 mm and fitted with intumescent strip since the 1980’s.

In the past differing gaps at the threshold (bottom) have been quoted, 6 mm was common but the latest guidance FD designated fire doors gaps at the threshold (bottom) should be 3/4 mm or should be in accordance with the manufacturer’s installation instructions for the particular doorset design.

For FDs designated fire door it should be the same as above but with cold smoke seals fitted, as well as the intumescent strip, to the sides, top and threshold of the door. When fitted, cold smoke seals should give an even contact with the floor but should not exhibit significant increased frictional forces that could interfere with the closing action of the door. So there will be no gap for air at all.

The relevant British Standards are BS 8214 2008, BS 4787-1 and BS 5588-11.

[Guest MarkT]

Hi, Can I cut the bottom of a fire door when installing if the floor is not level, or does this effect the integrity of the door. Many thanks Mark

[Tom Sutton]

This depends on how much you remove and threshold gap left, (the space between the floor and the door). If it is a FD30/60 fire door then the gap should not exceed 6 mm, if it is a FD30/60s then the gap should be filled with a cold smoke seal or a drop down cold smoke seal, if necessary. If a small amount is removed then it should not affect the integrity of the fire door.

Check out http://www.safelincs.co.uk/search.php?q=cold+smoke+seals+bottom+of+door+draught+excluder&a=products

[Guest bob]

Since fire doors should be certified, the level of undercut will depend on what has been tested and approved by the certifier/certificate. Check with the manufacturer/supplier.

[Guest wes]

Hi, I am having a new consumer unit fitted in the cupboard under the stairs. The electricity board states it must have a fire door fitted. The existing opening is 750w x 1680h. Obviously I can't cut that much off a standard size fire door, what can I do?

[Tom Sutton]

You can purchase bespoke fire doors check out http://www.safelincs.co.uk/fire-doors-with-30-minutes-protection-fd30/ .

[Guest Richard]

Hi I've got a fire door and want to rip it down through the middle in its length would I be able then to re edge it.it's not goin to be used as a fire door and doesn't need a fire rating.

[Tom Sutton]

It depends on the construction but if it is a fire door then it is most probably of solid construction and should be able to glue and pin a hardwood lipping to the cut but whats this to do with fire safety?

[Guest adam]

hi tom

I'm having some doors fitted in a loft conversion & I was wondering can the carpenter trim the top & bottom evenly approx. 75mm to fit into the frame, I also been told to fit a fire stripping were trimming has been done? is this correct

[Tom Sutton]

Without seeing the documentation that should accompany the fire door especially the global assessment it is difficult to give an opinion. If you are using fire door blanks the global assessment with tell you all you need to know and it is more than likely you will need to fit intumescent seals to the top of the door and smoke seals to the top and threshold if smoke control is required.

[Guest]

Nice ...I find it very informative..Glad to visit this forum..  actually through this i get very useful information..keep updating.

[Guest PaulGri]

Hi,

I've found your site to be very informative. I have a question about FD30 fire doors. I've recently had a fire inspection and need to fit a fire door to an understairs cupboard. This door is only 1685mm tall so is non-standard height. I could order a special door size but these are really expensive. Am I able to purchase a standard 1970mm tall door and cut it down to the required height (from the bottom)?

Thanks for your advice,
Paul