Do I need custom size doors?

15 Dec 2008
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United Kingdom
I need some FD30 doors to satisfy LABC.

It's a 1934 property and the doorways vary in size from 1955 x 718 to 1975-715 mm

The doors online all seem to state that a max of 2-3mm (depending on supplier) can be trimmed from any single edge.

My understanding is that doors are fitted with 3mm gaps around the sides and top and 10mm gap at the bottom so that brings height down to 1962 mm and width to 709 mm.

Common door sizes I've seen are as follows:
  • 1981 x 610
  • 1981 x 686
  • 1981 x 762
  • 2032 x 813
  • 1981 x 838

Which of the above sizes could I purchase to fit without exceeding the max trim guidance?

Do I need custom doors if I want to stay within the guidance?

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You can't trim 20mm of a fire door let alone both sides
Either change the linings or speak with inspector if they will except intumescent paint if doors are in good shape
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You better change lining because trimming a door to adapt to an existing frame is a pain in the backside.
Also, your existing lining will need repair where the hinges/lock are now.
From a carpenter point of view I've always preferred changing lining and door.
That way I can be sure to square the lining perfectly and have a nice even gap all around the door without much effort.
Some doors or lining are naturally warped, so if your lining is straight and the door slightly warped, it will not sit flush.
Same if your lining is warped and the door straight.
This can be adjusted at point of fitting if you replace both.
Also, once painted, the door, lining and architrave will all look the same, very difficult if you're reusing old bits, especially if you're staining/varnishing instead of painting.
The downside is that when removing old lining, most times the plaster around it gets damaged, but it's easy enough to fix that.
Not to be forgotten is the fact that the door lining, either new or old, needs sealing with fireproof material, whether that is mortar or fire rated expanding foam is a decision for the fitter.
So in any case you will need to remove your architrave to see if the gap between lining and wall needs sealing.
At that point, removing the lining makes perfect sense.
Last observation is that I used to charge the same for a new door whether with a new lining or keeping the existing.
That's because of the extra time it takes to adapt the door.
Ask the BI if fitting a commercial grade fire alarm will remove the need for FD30 doors; mine was happy with the alarm alternative and saved me about £10k
It was just for the purchase of the doors themselves; I never even looked at the linings. Modern prices would be more like 15k for 20 doors

A friend who runs a charity has just been rinsed a similar amount for about 10 fire doors, installed - she's converting a residential building into a community centre and the BI dropped the requirement on her at short notice, the joiners saw her distress and were delighted to help out. And they look awful to boot..
I think we’re shopping in different shops

The fire door already installed in the loft cost £172
Ask the BI if fitting a commercial grade fire alarm will remove the need for FD30 doors; mine was happy with the alarm alternative and saved me about £10k

What I should have done was installed interlinked smoke detectors in the rooms while there was access but this option wasn’t presented to me earlier.

I have them in the kitchen and each landing plus in the loft room but should have put them in the bedrooms and living room too
I had to to have both fire doors and interlink smoke an heat detectors
The other option is to attempt to bribe the BI. A couple hundred quid might make the problem magically go away.

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