Buckling, Sliding, and Thermal Tearing of Shingle Strips
In the featured photo the shingles exhibit buckling at the ends of the shingle strips. This buckling is similar to the buckling of a concrete roadway in the summer. The shingles have expanded from excessive heat or swelled from excessive moisture absorption. The lengthening of the shingle strips causes them to buckle upward at the joints between the strips. Sometimes the buckling is caused by the shingle strips rotating and pushing against the adjacent strip as it is sliding down the slope (Figure 1).
Shingle strips sometimes slide down a slope (Figure 2) when the nails pull through the shingle mat. In Figure 2 the nails have pulled through the shingle mat because the nails were placed so high (above the sealant line, Figure 3) that each tab is fastened with only the four nails driven into its surface instead of the eight nails.
Fastening with eight nails is accomplished when four nails are driven just below the sealant line and when the four nails are driven just below the sealant line of the overlying shingle and subsequently through the top edge of the shingle strip (Figure 4).
Thermal tearing of shingles is evidenced by a vertical and/or diagonal tearing through a shingle strip (Figure 5). The tear usually extends up the slope from a joint between two adjacent shingle strips (Figure 5).