18 BULLETIN 801;, V. S. DEPARTMENT OE AGEICULTUKE. 



tliese requirements are stated in connection with other materials 

 anel the clrfferent designs of walls. 



DIVISION FIRE WALLS. 



Division fire walls should extend from a firm foundation of con- 

 crete or other masonry to the underside of the roof, but need not 

 extend through the roof. The end of the division fire wall may be 

 built into the exterior wall where this exterior wall is of material 

 equal to that used in the division fire wall ; but if the exterior wall 

 is of even slightly inferior material, the division fire wall should 

 extend through to the outside of the exterior wall. Otherwise, divi- 

 sion fire walls for fire-resistive construction are not essentially dif- 

 ferent from division walls for other types of construction. The 

 division fire wall for a building of several stories may be constructed 

 solidly with floors resting on offsets (or corbels), or reinforced con- 

 crete floors may extend through the wall.* 



The proportions and design of the division wall should be adapted 

 to the general design of the buildings and the material available for 

 the wall. In no case should the division wall be less than 16 inches 

 in thickness except for reinforced concrete panel walls referred to 



^ The requisites for material for tlie construction of a division fire wall arc, 

 first, that it will not transmit lieat rapidly ; second, that it will not deteriorate 

 tinder the test either of quick and severe or of sustained fires ; .third, that it will 

 absorb lieat with sufficient uniformity to obviate dangerous difference in re- 

 sulting expansion between the protected side of the wall and the side exposed 

 to fire. Even with the best materials it is essential that the proixtrtions 

 and design of the wall be such as to resist the stresses resulting from the fire 

 and give sufli<}ient stability to the wall. 



Material best suited for division walls are hard brick (of clay or clay and 

 shale) laid in cement mortar, reinforced concrete, or plain concrete. AU of 

 these materials offer a strong resistance to the transmission of heat and are 

 not deteriorated by it to a dangerous degree. Furthermore, they absorb heat 

 with sufficient uniformity to prevent variation in expansion which results in 

 spalling, or the flaking off of large pieces. These are qualities lacking in many 

 stones, especially limestones and granites ; limestone will crumble when sub- 

 jected to heat and granite will break up badly. It is for this reasou, chiefly, 

 that division walls should not be constructed of stone. Mortar composed 

 largely of lime deteriorates from heat, and, therefore, brickwork should be 

 done with cement or cement-lime mortar. 



It is the requisite that a material absorb heat and expand uniformly that 

 is the chief objection to the use of hollow clay tile in division Sre walls. The 

 feature of insulation formed by the air pockets ov cells — which makes this 

 material so desirable for certain uses — totally unfits it for use in a division 

 wall. During a fire, the exposed shell of the tile expands very rapidly and 

 the air cell prevents sufficient absorption of heat by the protected portion of 

 the tile, with the result that the thin shell cracks or the wall buckles because 

 of the excessive expansion of one side. 



