When fitting a fire door, if you plane off the hardwood edge lipping, does this compromise the integrity of the fire door even if you still install intumescent strips?

Yes it will compromise the integrity of the fire door. Timber will char at a steady rate. However, in the case of an arris, e.g. at the leaf edge, heat energy will be supplied in two directions simultaneously, resulting in rounding of the arris due to charring at a rate apparently greater than that of charring on a flat surface. This phenomenon is recognized in BS 5268 - 4.1.

Hardwood is the normal material for door lippings because of its toughness and ability to resist wear and tear. Hardwood is generally denser than softwoods and therefore have a lower charring rate which is of additional value when considering fire exposure. Intumescent or heat activated fire seals and smoke seals may be fitted into door lippings. The thickness of the lipping will have to be sufficient to accommodate grooves that will accept the fire and smoke seals.

Lippings of 8 mm minimum thickness are generally found adequate and these are normally butt jointed to the door core edge. To ease the door a maximum of 3mm each side may be removed from the lippings but none from the top.

Test evidence substantiating the use of a particular form of construction when tested and incorporates lippings should not be considered to substantiate a similar form of construction where no lipping is incorporated.