Structural Flakeboards and Composites 3005 



Lateral resistance of 8d nails. — Carpenters frequently use 8d nails to secure 

 sheathing and decking to supporting structural framework. The American Ply- 

 wood Association (1980) specifies that APA RATED SHEATHING roof pan- 

 els, if more than 1/2-inch thick, should be fastened with 8d nails placed with 

 minimum edge distance of 3/8-inch. Price and Gromala (1980) provided data 

 relating lateral nail resistance of such nails at three edge distances, in dry and wet 

 panels of 1/2- and 5/8-inch thickness and of various designs (table 24-23). They 

 used a modified form of standard test ASTM D 1761-68 (American Society for 

 Testing and Materials 1968b) to evaluate lateral nail resistance in single shear. 

 Panel fabrication procedure was principally that described by Hse (1975c) and 

 summarized in footnote 1 of table 24-12, except that some of the flakeboard 

 panels were comprised solely of yellow-poplar, and others of southern pine. 



Price and Gromala found that the flakeboards offered more lateral nail resis- 

 tance when dry or wet than did southern pine plywood of equal thickness. 



For all types of sheathing material, average nail resistance decreased after 24- 

 hour water soak (table 24-23). Decreases ranged from 9 percent (5/8-in mixed 

 random high-density flakeboard) to 27 percent (1/2-in southern pine plywood). 

 Observed maximum lateral nail loads in both wet and dry tests generally in- 

 creased with the distance of the nail from the edge. 



For the flakeboards, dry lateral nail resistance did not consistently increase as 

 density increased. Since the high-density flakeboard groups generally lost less 

 lateral nail resistance after water soaking than low-density groups, wet lateral 

 nail resistance increased as board density increased. Perhaps, the high-density 

 specimens did not absorb as much moisture as low-density samples and thus 

 maintained better particle bonding. If so, thickness swell and density change 

 would influence the smaller decrease in lateral nail resistance for the high- 

 density specimens. Lateral nail resistance also increased as board thickness 

 increased for the mixed oriented flakeboards but not for the plywood or mixed 

 random flakeboards. 



Nail popping. — Flakeboard used for roof sheathing must be able to hold 

 shingles in place. Failure of roofing nails to perform this function is manifested 

 by nail "pop" — the slow natural withdrawal of a nail due to shrinkage and 

 swefling of the panel and shingles. Schaffer et al. (1980) studied the perform- 

 ance of 1-inch roofing nails that had been driven into and through commercial 

 and experimental flakeboards. They found that such panels exposed to cyclic 

 moisture conditions, including freeze-thaw, did not develop nail pop. Instead, 

 the nailheads were observed to subside further into shingle and panel surfaces 

 with increasing exposure. This subsidence was highly correlated to the thickness 

 swell of the panels. They concluded that nail pop will not be a problem with nails 

 driven through flakeboard. 



SCREW HOLDING 



Pages 1270 through 1281 of Koch (1972) describe load-carrying capacity of 

 wood screws in southern pine. For additional discussion of wood screws applied 

 to solid wood, see U.S. Department of Agriculture, Forest Service (1974, p. 7-9 

 through 7-12). No data specific to flakeboards made of southern hardwoods are 



