20 BULLETIX 801, U. S. DEPARTMENT OF AGRICULTURE. 
in height, frora floor surface to floor surface) or each increment of 
30 feet, the wall should be increased in thickness 4 inches. 1 
The foregoing thicknesses apply to a wall not more than 100 feet 
long. If this length is exceeded the thickness of the wall should 
be increased 4 inches throughout for each additional 100 feet or part 
thereof, except that for reinforced concrete the increased thickness 
may be one-half that stated above. 2 
While it is not intended to discuss here the matters pertaining to 
all details of a building code, it may be well to point out some 
dangers of poor construction in the division fire wall. Openings in 
division fire wall should be avoided as far as possible. It seldom is 
necessary to provide any openings in such a wall of a warehouse 
1 For the final 4 inches of thickness in excess of 16 inches pilasters may be 
substituted provided such pilasters are built with the wall, are opposite each 
other on both sides of the wall, and are located and proportioned suitably. 
Such pilasters should have a projection from the wall of 4 inches on each 
side, and the face (or dimension parallel to the wall) should be a minimum 
of 16 inches and not less than one-eighth of the spacing of the pilasters 
measured between centers. The spacing of pilasters should not exceed 23 
feet. The location should be such that no part of the? wall will be loaded 
beyond the allowable unit working stress of the material used. 
2 While stated thicknesses for walls seem arbitrary, the explanations made 
show that a division wall is subjected to more severe tests during a fire as 
the height or length of the wall increases. Difference in thickness of brick- 
work necessarily must be made in units of 4 inches, and so heights and lengths 
of walls stated are adjusted to this variation. Good practice has shown that 
the above thicknesses are very satisfactory for a wall serving as a barrier 
against fairly intense and continued heat. A wall of less thickness may afford 
good protection, but it should be borne in mind that a division fire wail should 
represent "the last line of defense" in a fire; and if the values behind the 
Wall justify the expense of a wall, then one which will afford dependable pro- 
tection is the best investment. 
An exception to some of the foregoing requirements for a division fire wall 
is found in panel-wall construction especially adapted to reinforced concrete 
roof and floors. The panels may be built of brick between supporting columns 
and floor and roof slabs or beams, after these have been constructed, or the 
panels may be of reinforced concrete cast with the floors. In such a case the 
stability of the wall and its action in resisting expansion is cared for by the 
concrete framework, and each panel of brickwork may be treated as a sepa- 
rate and independent division wall in applying the preceding requirements. 
These requirements for thickness, however, may be modified to the extent of 
permitting a brick panel wall to be only 12 inches in thickness, or a reinforced 
concrete panel 10 inches in thickness, for a height of 20 feet for panels not ex- 
ceeding 30 feet in length. The mortar used for laying brick walls of this 
character should be the cement-lime mortar described, as it is more com- 
pressive, and so in this confined position may withstand the severe compression 
from expansion. This form of construction usually will not be economical as 
compared with the regular division wall carrying the floors and roof, except 
in case the building is more than four stories high or the wall is excessively 
long or there are such special conditions as are discussed under the heading of 
roof and floor construction. 
