To a roofer, carpenter or a handy homeowner, the humble shingle is a joy forever—well, maybe not forever. Sooner or later sunlight and weather will degrade it, but better examples of the breed last for decades. The typical three-tab asphalt shingle is made from asphalt-impregnated felt (or fiberglass) covered by mineral granules. Each is nailed to a house’s roof deck in such a way that the shingle above covers the nails. This way, water running down the roof runs over each successive course of shingles, right down to the gutter. A row of mastic tabs on top of each shingle helps seal it to its neighbor and helps the combined roofing assembly resist wind uplift.