Leaks. Leaks can be caused by a number of factors, including problems with flashing (metal placed in trouble spots, such as sharp angles in the roof) and with loose nails. Each time a roof is heated and then cooled, or each time the moisture content changes, the decking expands and contracts. With each expansion and contraction, the nails are pulled slightly out of their holes. Once a nail is pulled out of its hole far enough to puncture the shingle above it, a leak develops. Fortunately, over the life of a properly installed roof, nails rarely pop up far enough to puncture shingles. However, during the tear-off process, pieces of the decking may be loosened. All loose decking should be renailed to the rafters with new cement-coated sinkers, or the equivalent, prior to new installation. To reduce the cost and underbid the competition, some less-reputable companies may not renail loose decking. Instead, these companies simply hammer down the nails that pop up during tear-off.
Roof life. Roof life is determined by a number of factors, including proper roof installation, decking quality, shingle life, proper ventilation, flashing quality, and routine maintenance. Routine maintenance includes inspection for problems, as well as leaf removal and gutter cleaning. Proper ventilation extends roof life. If the roof is not properly ventilated, most shingle warranties are voided. Among the various available grades of shingles, high-quality shingles are warranted for 40 years or longer. According to some industry sources, shingles rarely last for as long as they are warranted.
