A roof tank is a necessity in tall buildings and in many six-story buildings. They are also needed wherever a Flushometer valve is used. These tanks are built either of cedar wood or of boiler iron, and should be frost-proofed with a double bottom and top and a double lining at the sides, thus creating an air space, or by running a steam coil to the top of the tank, or by putting the tank in a heated pent-house, built especially for it.

The law requires the bottom of all tanks on fireproof buildings to be 20 feet above the highest outlet of the fire standpipe line on the top floor, so as to give the necessary pressure. This explains why tanks on fireproof buildings are put up in the air, disfiguring the building from an artistic standpoint, but being very necessary for adequate fire protection.

Note should be taken that the water tanks are adequate in size, and properly protected from frost.