A second layer of shingles, also called a layover or overlay where new shingles are installed over an existing layer, generally has a shorter lifespan than a roof installed with a complete tear-off to the deck. While a first layer of architectural shingles might last 22 to 28 years, a second layer typically lasts 15 to 20 years, representing a 20 to 30 percent reduction in lifespan. Several factors cause this reduced longevity. First, the second layer cannot lay perfectly flat over the uneven old layer, which prevents proper sealing and makes it more vulnerable to wind uplift. Second, the extra layer traps more heat, as there are two layers of asphalt absorbing and holding heat, which accelerates aging of the new shingles and can overheat the attic. Third, you cannot inspect or repair the deck, so any existing rot or moisture issues remain hidden and can worsen. Fourth, manufacturer warranties are often reduced or voided for overlay installations, as manufacturers require installation on a clean deck for full warranty coverage. Building codes allow a maximum of two layers, but most roofing professionals recommend tear-off for best long-term value despite higher upfront cost, as a tear-off allows installation of new underlayment, proper deck inspection, and better ventilation, resulting in a roof that reaches its full rated lifespan and has full warranty protection.
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