48 BULLETIN 801, IT. S. DEPARTMENT OE AGRICULTURE. 
which would not collapse quickly. Even then, it should be adopted 
only with great reluctance. The roofing most fully suited to the 
requirements of the nearly flat roof of the cotton warehouse is 
tar and gravel of good material carefully applied. Its cost of upkeep 
is very low, while with a tin roof the cost of painting required is 
considerable. 
The junction of roofing with parapet walls should be made water- 
tight by extending the flashing an ample distance up the side of the 
wall and counter-flashing with suitable material built into the brick 
joint or suitable recess. 1 
ROOF OPENINGS. 
Roof opening for the storage or compress compartment of slow- 
burning construction should conform in all particulars to the requi- 
1 There is now on the market a type of tile, or wall block, which provides a 
" raggle joint " for holding counterflashlng. The eaves of the roof may extend 
even with the outside of the exterior wall and be finished with a hanging gutter 
fitted close to the top of the wall, or the exterior wall may continue above the 
roof to form a parapet. When this latter and better method is adopted, care 
should be exercised to provide ample capacity for the outlet conductors in 
order that excessive water may not accumulate on the roof and encroach above 
the flashing. As a further safeguard against such an occurrence if conductor 
pipes should become clogged, scuppers or openings should be provided through 
the parapet, the inner end of the scupper lining being soldered to the flashing 
and the outer end arranged to discharge water freely. 
The scupper preferably should be about 5 inches high and 12 inches wide and 
should be so set that the top of the opening would not be above the top of roof 
flashing and the bottom would not be so low as to permit discharge from the 
scupper except in the event of stoppage of conductors. 
Flashing and counter-flashing should be of durable material and usually 
should be metal. Copper is the best material for this purpose, but its cost at 
this writing makes its use prohibitive. When used it should be of the thickness 
known as 16-ounce, the " hot rolled " metal being suitable. Galvanized iron 
makes an excellent and economical flashing. Its thickness should be from 
24 to 27 United States standard gauge. Care should be exercised to see that 
the material used does not show cracking or flaking off of the zinc coating 
when the metal is bent in the necessary manner. Roofing tin may be used, but 
is less desirable than the other materials mentioned. Such tin plates should 
be of the quality known as " 40-pound " tin coating, and this coating may be on 
the lighter weights of sheet iron. Tin flashing always should be well painted 
on both sides. Joints in any flashing should be soldered and allowance made 
for expansion. The counter-flashing (which is built into the wall and turned 
down over the flashing) should be in long but independent sections, well lapped 
at joints. Guttering should be of galvanized iron, usually of No. 24 United 
States Standard gauge. 
It is of great importance that there be no penetration of water at the junction 
of roof and parapet. Although the resulting damage to the cotton may be 
negligible, such moisture causes rapid decay of the ends of timbers, with a 
frequent result that such timbers which are otherwise sound must be replaced. 
