The roof must be brick-arched, and the arches should be made in the strongest possible way, in order to resist if necessary the weight of a great portion of the building above falling on them. If the span cannot be from one wall to another, then a wrought-iron girder may be introduced, but should be most carefully covered by cement or plaster at every exposed part. On no account use a cast-iron girder.
The entrance to the room has to be well protected, for it is here that attack is to be expected from thieves, and that fire might possibly creep through.
The best plan is to use a fire-resisting door and gate joined together; the door being flush with the outside of entrance and opening out, the gate flush with the inside, and opening inwards; as a general rule the door only is used, but the addition of a gate not only gives extra security, but allows the door to stand open in the daytime to ventilate the room, when other openings for ventilation are impossible or undesirable. There certainly should not be any other direct opening besides the doorway either for light or air. Light is, I know, frequently desirable, but if it is obtained through a window or skylight the strength of the room is lessened, even if these openings have strong iron shutters. If gas is to be introduced the pipes must be laid on with care; it is best to have no pipe inside, but a swing bracket outside the entrance, which, when the door is open, can be swung through the opening and thus light up the interior. Fixed lamps may be used, but there is a certain amount of risk—though it is small—of their being forgotten, and of sparks from them igniting loose papers. It will follow from this that no stove or fireplace should be used inside a strong-room; for if there is a flue a source of weakness is introduced, besides the contents of the room being liable to damage from fire.
But the fixing of the door is an important and hitherto much-neglected point. The annexed drawing shows almost at a glance the proper mode of doing this:—
I have taken it for granted that it is understood iron doors are made with a frame surrounding them of bar-iron, to which the hinges of the door hang, and the corners of which project, to give greater strength. Now, if this door and frame be fixed while a building is in progress, the locks and bolts are exposed to injury from dirt and damp, and the frame is liable to be thrown out of position by settlement of the wall. It is, therefore, better to leave such an opening as shown in the engraving sufficiently large for the intended door-frame, toothed at the sides, and having an arch above it. The door can then be fixed when the building is nearly ready for occupation, the surplus opening being filled with brickwork. The drawing shows a stone sill, and it is usual, though not necessary, to fix a stone lintel over the top of the door, as shown by dotted lines; or the arch may all be filled with brickwork. The bottom of the frame should be grooved about two-thirds of its thickness into the sill, leaving enough room for the door to open clear of the floor-level; or if it be wished to let the bottom frame entirely in, the same end may be obtained by slightly sloping away the floor outside it. The top and sides of the frame should be rebated into the head-stone (or brick) and jambs the whole of their thickness, so that the inside of the wall-opening may be flush with the inside of the frame.
The door must be placed level and upright in the position prepared for it, and temporarily supported there; it should be received from the makers locked, and must have its brass furniture fixed, and be unlocked by the key before attempting to turn the handle of the main bolts. If after unlocking it there is any difficulty in turning the bolts back with the handle, no great force should be used, but the position of the frame must be adjusted until the bolts move easily and the door opens without binding anywhere. In case of any such difficulty, a little wedging up of the top arm against the shutting side of the door (marked A in drawing), will usually remove it. Try the door with a spirit-level applied to three parts, viz.: 1. The face or edge of frame (right and left sides), with door shut. 2. The inside shutting edge of frame, with door partly open. 3. The inside of bottom of frame; and adjust until the bolts work properly. It should then be fixed in this position, taking care not to force the sides of the frame inwards while so doing.