SPECIALTY ROOF DECK DETAILS (CONT'D)

Exterior grade sheathing panels are ideal for this purpose, since they provide a strong, smooth surface. However, under certain conditions of pitch and loading, there may be a tendency for the entire roof above the decking to creep downwards, bending the nail fastenings and compresing the insulation, thereby reducing its efficiency. In such cases, it is often desirable to install the vertical members as previously described.

Nails

If the shingles or shakes are nailed directly through rigid insulation, a number of problems may be encountered. For instance, the longer nails have thicker shanks which tend to split the shingles or shakes. In addition, movement of the shingles or shakes as they go through natural expansion and contraction cycles caused by wetting and drying, have a tendency to enlarge the holes in the insulation, thereby reducing its efficiency. For this reason, the use of strapping or a false plywood deck is again recommended.