The ceilings of the fire and heat-proof floors, which, when there are other apartments above, _must_ be provided over the hot rooms, may be of plaster. But the heat at the ceiling level is very great, and the plaster here rapidly darkens and blackens, and in this state looks anything but attractive in a place where the mere suspicion of uncleanliness is nauseating. If employed (and this remark also applies to plaster on walls), it should be used in the simplest manner possible, without the slightest attempt at modelling the surface. Enamelled iron may be used, with effect, for ceilings. The little laconicum is best covered with a flat vault, the soffit being of glazed bricks, and the springing being brought down below the main ceiling level.
Fire-proof floors over hot rooms may be of any design that is also heat-proof. The main point is to have a sufficient thickness of concrete, and the iron joists and cross girders well buried therein. Ordinary floors may be rendered heat-proof by partially filling the space between ceiling and floorboards with sawdust or sheets of slag-wool laid on boarding nailed to fillets on the joists. The sawdust should be filled up to the top of the joists; over this a layer of thick felt, and the boarding above. This, however, is only a makeshift when compared with a solid floor of concrete.
When the hot rooms are in a basement in the open, they may be top-lighted, and the ceiling above need not be a heavy fire-proof construction. A sufficient air space, however, must be provided between the ceiling and roof, to prevent irradiation of heat--a remark that applies also to anything in the shape of a window in the sudatorium. It must be double, or look into an area covered with pavement lights. In the case of a top-lighted room there must be a ceiling-light and a skylight.
Where the hot rooms are constructed quite above ground, consideration must be given to the prevention of loss of heat by radiation. This may be effected by providing thick hollow walls, the cavity being often usefully employed for the extraction of the vitiated air.
Heat permeating other apartments and neighbouring premises is a frequent source of trouble to the builder of a Turkish bath, but is always the result of want of study of the subject on the part of the designer. The evil may be successfully combated if it be resolved that no hot room, shampooing room, or lavatorium shall be constructed without a thick concrete floor above, and that the furnace chamber be perfectly and completely insulated. Should the walls of the hot rooms adjoin apartments to which it is urgently necessary that the heat should be prevented from being transmitted, they may be rendered heat-proof by building them hollow and filling the cavity with soot.