Fire door details are specific to the doorset, and the single most useful thing a specifier or an installer can know is that the manufacturer's installation instructions are the detail. Generic drawings are a starting point and the certification is the authority, because the assembly was tested with particular fixings at particular centres into a particular supporting construction.
The frame to structure junction
The frame is fixed to the structure with fixings of the specified type at the specified centres, with solid packing at each fixing so that the frame cannot deflect. The gap between frame and structure is filled as the certification requires, which may be intumescent mastic, mineral wool or a specified foam, and is then covered by an architrave that is itself part of the detail in some systems. Foam alone with no packers is the classic defective installation.
Gaps around the leaf
Head and jamb gaps are held within a narrow band, and the threshold gap is separately specified and is larger where smoke sealing is not required and tighter where it is. These are small dimensions and they are measured rather than judged. A gap outside the range at any point is a defect, and a gap that varies along its length indicates movement in the frame or the leaf.
Apertures
Vision panels, air transfer grilles and letterplates are holes in a tested assembly and each needs its own tested solution: the correct glass in the correct beads at no more than the tested area, an intumescent grille of a tested type, a letterplate tested with that doorset. Cutting an aperture on site into a certified leaf is outside the certification unless the manufacturer's instructions expressly allow it.
Threshold and floor finishes
A doorset tested with a particular threshold arrangement has to be installed onto a floor that matches it. Adding a thick carpet or a raised floor finish after installation changes the threshold gap and can stop the door latching, which is a common and easily missed consequence of a refurbishment done by a different trade.
Questions people ask about fire door detail
Where do the gap dimensions come from?
The doorset's own certification and installation instructions. Generic figures circulate widely and the certification is what governs for a specific door.
Can a fire door be trimmed to fit?
Only within the limits the manufacturer states, which are small and often apply to one edge only. Trimming beyond that ends the certification.
Does the architrave matter?
In some systems it is part of the tested assembly and covers the perimeter seal. In others it is cosmetic. The instructions say which, and that is the only reliable answer.