56 FIRE-KESISTING iiUlLDINGS. 



Roofs. — For ordinary roofs no better material than rein- 

 forced concrete is known, though, having no loads except snow 

 or hail to carry, the construction would naturally be of a lighter 

 description than that of floors. The outer surface requires the 

 ap]jlication of weather resisting material to it, of which none 

 better than natural asphalte exists. Such a roof, without the 

 asphalte, will prevent the spread of fire from, or to. any roof 

 that nlay be constructed above it. 



-V test made by the British Fire Prevention Committee in 

 1902 showed that a flat roof was constructed with deal joists 

 (as a floor), and covered with i^" boarding and three thick- 

 nesses of asphalted felt, finished with 23//' of sand and gravel. 



The underside was protected with wooden laths ij4" X 

 34", to which was applied i" of lime and sand plaster, with a 

 small admixture of plaster of Paris. When dry, the structure 

 was exposed to a fierce fire, with a maximum temperature of 

 1,500' F. for 1 hour. 



In 40 minutes the plastering began to fall, and at the ter- 

 mination of the hour's exposure the fire had not passed through 

 the roof, and it was sound enough to be walked upon. 



Stairs. — Stone, especially of the calcareous description, 

 must not be used for stairs, for if subjected to intense heat, 

 though they may appear to be intact, they may collapse when 

 stepped upon, or when water is applied. Concrete stairs, with a 

 small T iron in each riser, are quite reliable. The landings 

 should l)e of reinforced concrete, as to tlie floors, and at least 

 6" thick. All doorways and ])assages oj^ening upon staircases 

 should be fitted with self-closing, fire-resisting doors, and the 

 ceiling, at roof level, should be of concrete. These precautions 

 prevent draught, and the spread of fire from floor to floor. 



Walls and Partitions. — No safer material than brick in 

 cement mortar exists for outside walls, though terra-cotta, 

 backed with brick or concrete, is an excellent substitute. 



For solid internal partitions, bricks, slabs of ])orous terra- 

 cotta, or fireclay, concrete of suitable material and cement or 

 gy])sum plaster slabs are safe, and for hollow partitions the 

 following are recommended : — Hollow terra-cotta slabs ; ex- 

 panded metallic lathing on both sides of steel studs, plastered 

 with suitable material, and with air space between ; sheets of 

 compressed asbestos and cement secured to uninflammable im- 

 pregnated wooden studs. In all the tests made, it api)ears that 

 water aiJ])lied to plaster when hot does as much, or more, damage 

 than the fire itself. 



The following list of tests, made by the British Fire Pro- 

 tection Committee, speak for themselves, and prove that the 

 a])plication of water had the least eft'ect upon No. i (the hollow 

 porous terra-cotta tile partition). 



No. I. — Partition of hollow porous terra-cotta tiles, 12" _X 

 12" X 2]4", laid in cement i to 2, plastered on fireside with 

 M" of asbestic, sand ar.d .'?rc\- lime The tiles were rendered 



