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Fire Doors

Guest Ian.m.

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Guest Ian.m.

Hello, i would like to ask a question about the construction of fd30 doors, why is there only an allowance of 5-8mm genualy to be able to trim off the bottom?

I am a carpenter/joiner with 26 years behind me in fitting doors. In that time its a novelty to fit a house out with new doors and not trim for thick carpet-hard wood ect.

would it be that difficult to increase the solid timber at the base of a fire door to give 25mm tolerance to cut.

For a start an fd30 frame is normally around 5mm thicker than a standard frame so your already on a loser and genuraly the frame is tight to the lintel.

Are the companies that make fire doors expecting clients to pay for raising lintels, fitting new floor coverings through out.

All for the sake off 25mm of softwood.

Thanks Ian






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It all depends on the construction of the timber fire door they usually consist of a fire resistant core with hardwood lippings on the stiles and softwood lippings on the top and threshold, covered with a veneer cover. I see no reason why they could not put larger lipping on but that is up to the manufacturer's, I think they just construct then to standard sizes. Which is alright until you have to hang doors in old buildings that are not standard then it's time to consider fire door blanks and make your own.

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Hi Ian

I asked our fire door specialist. Here his answer:

"Unfortunately the amounts Ian mentioned are only an average; the actual amount that can be trimmed from a fire door differs from door to door, even if they are supplied by the same manufacturer. Rather than strictly relying on the materials, methods, and other components used during construction, the amount of excess is determined during testing of a finished fire door. During the tests, some material is removed from the edges of the doors until integrity is lost and the door cannot hold back a fire for the 30 or 60 minutes required.

Due to the nature of fire doors and the regulations for their use, testing and integrity are fundamental to the selection of a fire door and subsequent liability in any legal action caused by a fire in the building. Large amounts of excess cannot be added to the edges as this material will likely not meet the standards required to uphold a door’s integrity. Test certification for a door will state the amount of material that can be trimmed, and this can only be provided on a per-door type/size basis to ensure the certification aligns with the exact constitution of the door you receive. "

Traditionally, there had been standard amounts that could be cut-off, especially at the bottom of the door, however, due to the lightweight design of some modern fire doors, some fire doors will hardly tolerate any modification.

So if your required fire doors are not exactly standard sizes you either need to order fire doors made to exactly your required dimensions or you need to find out from the retailer/manufacturer exactly how much can be removed.


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Hi Ian, I understand your frustration. I have been in the fire door industry since January 2004 and have seen more incorrectly installed doors than correct ones. Even though manufacturers provide installation instructions, doors are still found to be non-compliant and therefore increasing the risk of premature failure in a fire.

The reason why there are such strict limitations to edge trimming on some doors (generally speaking) is that many of the standard sized doors have a lightweight-core construction that is dependant on perimeter timber framing around the core for fire performance integrity. In order to keep prices down the framing section used is the minimum required to pass the 30 minute fire performance test. A fire door, just like a tonne of sand, is a commodity item when it comes to buyers from large construction companies needing to buy at the lowest price.

However if you go 'upmarket' you can purchase solid core fire door blanks that have much greater trim allowances. You can then produce a non standard sized door but you must carefully follow the manufacturer's instructions. Always ask the supplier for them when you buy. Some suppliers aren't at all clued up on fire doors so only buy from suppliers that will provide the correct installation instructions and product data sheets. Fire doors are life safety devices so don't take chances.


Tube core door.PNG


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