48 BULLETIN 801^ U. S. DEPARTMENT OF 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, Avhile 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.^ 



ROOF OPENINGS. 



Eoof opening for the storage or compress compartment of slow- 

 burning construction should conform in all particulars to the requi- 



^ There is now on the market a type of tile, or wall block, which provides a 

 " raggle joint " for holding connterflashing. 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 pui'pose, 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 

 Avhen 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 alwaj^s 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 

 doM^n 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. 



