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The Thickness of Nominal Fire Doors

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Our building inspector has asked us to upgrade several door sets to FD30 in our 1909 house. For most of these I would much rather do this by upgrading the existing doors to nominal Fd30 doors and am confident that I have the practical skills I need. A previous inspector had said this would be fine and that there would be a straightforward solution for our doors. The problem I have is that the doors are all a little over 30mm thick.

Why are nominal doors normally required to be 44mm thick or more?

Is the requirement for a nominal fire door to be 44mm thick or greater an absolute rule, or is there a way round this? 

Thanks in advance 



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Timber is an excellent material for fire doors because from empirical evidence we can easily predict its likely behaviour in a fire.  When subject to fire the timber will burn and a char will form on the burnt surfaces, eventually the burn-rate will cause the door to shrink in size and bow/twist towards the fire...........and then it will fail to provide fire separation.

The burn rate of the timber will depend on its density. Therefore the less dense the timber and the thinner the door, the earlier the door will fail and for that reason fire doors are generally at least 44mm in thickness and made from solid timber-based material.

When upgrading timber doors to fire resistant doors , it is important to consider the fire performance test evidence for the products used to facilitate the upgrading works.  All such products have limitations to their use/performance and the door that is to be upgraded must be comparable in its construction (density, thickness construction type) to the door that was successfully fire tested.  Look carefully at the evidence of fire performance for the proposed upgrading products and check they have been successfully fire tested when used with a door of similar type, construction, density and thickness to yours.

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Hi again Peter,

Just to add:  The doors as you described them would not be classified as Nominal Fire Doors.

A Nominal (or Notional) Fire Door is one where there exists no evidence of fire resistance performance but that in the opinion of the Competent Person would meet the required fire resistance performance.

What you describe, is a door that has been upgraded to a fire door using products that have evidence of fire performance when fitted or applied to that particular type of door. 

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