With reference to the guidance on loft conversions, when providing new fire resisting doors in an existing dwelling house, is it also necessary to replace the existing internal door frames?
A fire-resisting door should be regarded as a complete installed assembly. Thus the door, the frame and any ironmongery should be considered when assessing its suitability. In most cases, however, it should be possible to retain the existing frame. If in doubt, the test report for the door being installed will include details of the door frame in which it was tested.
Fire doors are often thicker and much heavier than other internal doors. Where existing frames are retained it may be necessary to replace or relocate the door stops and to install additional fixings back to the structure. The joint between the frame and the surrounding structure should be adequately sealed and the operating gap between the door and the frame should be kept to a minimum (usually 3-4mm).