Your inspections will reveal whether the entire roof is due for replacement. Different types of roofs have different lifespans:

Asphalt composite shingles need to be replaced when surfaces have eroded away; first the granules on the surface disappear and then the shingles themselves wear down. The first places to wear out are the surfaces below the decorative cutouts or at the ends of shingles. When holes have eroded through the shingles, abundant leaks are imminent. Although asphalt composite shingle roofs typically last more than 20 years, a roof can last less than 15 years or more than 50 years, depending on how hot the roof gets, the quality of the original roofing materials, and other factors. Even before holes appear, your roof is a goner if shingles appear gray and bloated, or if a piece of shingle crumbles easily between your fingers.

Wood shake or shingle roofs may go bad from drying out and splitting or warping. As shingles curl, they pull out nails and blow away. When you begin to lose shingles, it may be time for a new roof. Wood shake or shingle roofs occasionally last as long as 50 years, but can fail much faster if located in a shady area where dampness, rather than drying out, is the problem. Under these circumstances, you may need to have a roofer treat your roof with a preservative spray every three to five years. It is not uncommon for roofs that cannot dry between rains to become mossy and rotted within 10 years.

Tile or slate roofs can last indefinitely (though individual pieces may have to be replaced).

Metal roofs need to be replaced when they become riddled with holes too difficult to patch; if maintained properly, they, like high-quality slate and tile roofs, should last indefinitely.

Built-up roofs (composed of layers of hot bitumen and roofing felt, usually topped with stone) need to be replaced when they become so dried up and cracked that multiple leaks develop. Other telltale signs are blisters and places where the layers have delaminated. A four-ply built-up roof should last 20 years or more.

Single-ply and modified bitumen roofs usually fail first at seams and around drains. Look for separation at seams and bubbling or cratering of the membrane. Single-ply and modified bitumen roofs should last 20 years or more.