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Fire Doors to Fit Odd Sized Frames


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I'm replacing some doors in my house in the event I ever rent rooms out in the future. The old doors were fire doors and have now been disposed of. The questions I have are:


1) The frames around the doors aren't fire frames. Is that a problem? Not sure why my father installed fire doors without fire frames but if I can avoid the hassle of replacing the frame, that would be good. 


2) The measurements are standard for most of the doors in the corridor but in one room, the size of the gap is: 

Width: 765mm

Height: 1945mm

Depth: 44mm

The standard door is 1981mm high but I can only cut 10mm off the bottom giving me 1971mm. I then can have a gap of 3mm at the bottom, giving me 1968mm. The difference between 1945mm and 1968mm is 23mm. What can I do about that 23mm? Can I plane back the door frame by that much along the top? I really don't want custom doors.


3) In another room, the size of the door gap is:

Width: 700mm at the top/710mm at the bottom (the door space isn't straight)

Height: 1970mm

Depth: 44mm

The problem here is the width. The standard door comes in 762mm width or 686mm width. The larger size is too big as I can only cut down 4mm at either side of the door. The smaller size leaves a gap of 14mm/24mm. If I leave a gap of 3mm on each side of the door, that's a gap of 8mm/18mm remaining. Can I insert a slice of hardwood to the frame to deal with this?


4) Do I need intumescent strips, intumescent paint and fire rated hardware for the doors?


Many thanks for any advice.


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To clarify, there are five doorways, three of which I need fire doors for and two of which are bath/toilet combo. The reason I'm trying to accommodate somehow is that I want all the doors to match. Fire door blanks are so ugly! 

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6 hours ago, Neil ashdown said:

You say the frames are not fire rated. How do you know this?

Why not have custom made doors?

I asked my dad. He said they weren't. He didn't have them specially installed. It's an old 1920s cheap-built metro land property in North London. 

Too expensive. I don't know how long we'll keep the house. We don't hugely love it.

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The problem is that many of the standard sized fire doors cannot be trimmed above approx 3mm off each vertical edge and 6mm off the bottom. 

There are minimum requirements in terms of the thickness of the hardwood lippings and because many fire doors have small section framing around a chipboard core the trim allowances are very limited. If you trim too much then the door will be weakened and therefore not provide the required performance. 

You could possibly fit new fire door frames to suit standard door leaf sizes, depending on the structural openings. If the structural opening sizes won't work for standard sized doors then, sorry looks like its gonna be door blanks.

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