18 BULLETIN SOI, IT. S. DEPARTMENT OE AGRICULTURE. 
these requirements are stated in connection with other materials 
and the different 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. 1 
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 
1 The requisites for material for the construction of a division fire wall are, 
first, that it will not transmit heat rapidly : second, that it will not deteriorate 
under the test either of quick and severe or of sustained fires ; third, that it will 
absorb heat 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 proportions 
and design of the wall be such as to resist the stresses resulting from the fire 
and give sufficient 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. All 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 reason, chiefly, 
that division walls should not be constructed of stone. Mortar composed 
larselv 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 fire walls. The 
feature of insulation formed by the air pockets or 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. 
