Register Plates
One modification for such (to us) overlarge chimney voids is to fit a hood or a stove, and in each case, the chimney has to be closed off so that air from the room does not go around the stove or hood.
This is achieved by fitting a false ceiling called a ‘register plate’, which is usually a horizontal sheet of metal that is pierced by the neck of the hood or the stove fluepipe.
It has to be mentioned that this sheet should be made of metal, because occasionally such plates are made of wood planks, plywood, plasterboard or other unsuitable material which, being flammable, have an excellent chance of igniting. Fireproof materials which resemble asbestos sheet (but without the health risks) are available, but are not in practice suitable. They are vulnerable to rain falling down the flue, they can have a tendency to crack if they get hot, and above all they are not always strong enough to resist having brushes and rods pushed through their access points.
Again, these plates should be made of metal and be thick enough to resist sagging and the inevitable corrosion. They should NOT be supported on wooden battens, but on metal supports, and where these are fixed to the wall, plastic rawlplugs can melt.
Access Hatches
These MUST be big enough, ideally 9″ x 9″ as a minimum.
They should be closed off by lift in, lift out loft door type access hatches held in place by gravity. (PLEASE, no screws, no bolts, no catches, no hinges, no runners, just square, simple lift out hatches).
Threads freeze solid with heat, as do sliding doors, and we risk damaging the register plate if we have to use force to open them. On most plates, two hatches are needed, but where the plate is particularly wide, a third one can be useful. If you only have one, it can be difficult if not impossible for us to remove the soot each time, and it there is no access at all, then soot can build up until it catches fire.
This plate fire can turn into a chimney fire with all its associated problems. Worse, there will be no way for the fire brigade to deal with such a problem without ripping out the entire plate with all the mess that can entail.
