I’m a second-generation roofing contractor, a certified installer of most common types of roofing. In this article, I’ll discuss what it takes to apply a guaranteed, watertight asphalt-shingle roof. While basic installation guidelines are printed on every shingle wrapper, there’s a lot more to know if you’re really interested in preventing callbacks. About 80 percent of our asphalt-shingle installations are replacement jobs working directly for the homeowner in which we use laminated “architectural” shingles — by far the most popular roofing choice here in New England.

Roofs age differently under different exposures and in different climates, but the roofs we replace are generally between 20 and 30 years old. Although shingling directly over an old roof eliminates the considerable effort and expense of stripping and disposing of the shingles (building codes permit a second layer only), we strongly discourage...

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