If the granular surface of asphalt shingles is worn and if shingles are cupped and dog-eared, it’s time for a new roof. Ditto if gutters contain a significant amount of gravel washed off the surface of the shingles.
If the roofing is lumpy and uneven, it probably has two or more layers of shingles that weren’t well installed and so need to be stripped to the sheathing before reroofing.
Do you see odd-colored shingles? If so, they are probably patches over old leaks. Or if the roof is relatively new and shingles are worn in only one area, perhaps one bundle of shingles was defective.
A roof less than 5 years old with a large number of loose or missing shingles indicates that the installer’s power nailer was set too deep and drove the nails too far through the shingles. In this case, that roofing needs to be replaced.
If there are two or more layers of roofing, strip the roof to its sheathing before reroofing. The best place to count layers is along the edges. But, as you count, keep in mind that roofers often double the shingles along the edges, to stiffen the shingle overhang so water drips freely off its edge.
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Flat roof is a misnomer: Even relatively flat roofs need some slope so water can exit down a drain or gutter. (After all, a cubic yard of water weighs 1,684 lb.) Still, water tends to pool on such low-slope roofs, so their roofing membranes must be intact to keep water out.
