INTERIOR WORK OF BUILDINGS.
has heretofore been made to this subject in con nection with the discussion of proper supports of floors, the weight they' should be able to bear, and the methods adopted in Paris for diminishing fire-risks and preventing sound from readily passing from one story to an other (p. 46).
Strength of primary consideration is strength. An indica tion of the requirements deemed essential is furnished by the statement that the New York building law provides that in all buildings every floor shall have sufficient strength to bear safely upon every superficial foot of its surface seventy-five pounds, and, if the buildings are used as places likely to be visited by large numbers of persons, one hundred and twenty pounds. In reference to the supports of floors, the building laws of the cities of New York and Boston require that in all buildings more than 3o feet in width, except car-stables, churches, theatres, schoolhouses, and other public buildings, the space between any two of the bearing walls shall not be over 25 feet unless girders are substituted for the partition-walls.
['aria/ion Strength of is a great variation in the actual requirements for strength in the floors of the buildings of different classes, the extreme range being, according to one of the estimates, from forty pounds per square foot in dwellings to four hundred pounds per square foot in factories. In cases where unusually heavy weights will probably be applied, safety should be assured by a proper apportioning of the strength of floor beams and the floor to all possible demands. Neglect of this duty, the natural effects of decay, and the weakening- influ ences of alterations in various buildings arc the primary causes of a con siderable number of so-called "accidents" in which persons are injured or killed. Text-books contain rules by which the strength of floor beams can be calculated and due allowance made for the factor of safety. The aver age weight of the floors in dwellings is estimated at from seventeen to twenty-two pounds per square foot of floor, including the weight of the plastering. on the under side. For ordinary spans the weight is frequently about twenty pounds, and for long spans about twenty-two pounds, per square foot. In public buildings the weight per square foot seldom exceeds twenty-five pounds. Factory or warehouse floors required to sustain heavy
loads sometimes weigh from forty to fifty pounds per square foot. All floors in first-class buildings should possess not only sufficient strength to resist fracture, but also sufficient stiffness to resist bending under any load to an extent that would cause the ceiling underneath to crack or to present a bad appearance to the eye. To insure appropriate safeguards, the thickness and weight of the material used in American floors are frequently propor tioned to the superficial load the floor is intended to bear.
Classes of Flooring. —ln English practice, three kinds of floorirn; are extensively used ; they are classed as " single flooring," " double flooring," and " frame flooring." The first, or single flooring, is supported solely by a row or tier of joists extending from one wall or partition to another, and it receives the flooring boards on the upper surface or edges of the joists and the ceiling on their lower surface. This form of flooring does not provide for the prevention of the transmission of sound from one story to another, and the joists used are sometimes too thin fully to serve all desirable purposes. Double flooring consists of three distinct. series of joists, called " binding," " bridging," and " ceiling" joists. In this sys tem the binders are the real supports of the floor; they run from wall to wall and carry the bridging joists above them. Frame flooring is a con struction of girders with binding, bridging, and ceiling joists.
Improzyyl Flooring. —Notable improvements in the construction of the floors of factories, warehouses, stores, and large buildings in business centres intended for the use of ninnerons tenants as offices, etc., have been extensively introduced during a comparatively recent period. They em brace better provisions against the dangers of fire and better methods for preventing the transmission of sounds and vibrations than were formerly common. In some forms of fireproof floors the principal materials used are brick and hollow terra-cotta tiles, supported, usually, by iron beams (pi 2, Jig. 3). In others considerable quantities of mortar are intermingled with the foundations of wooden floors.