A square of shingles weighs between 200 and 350 pounds. The weight of a shingle is generally an indicator of its life expectancy. Shingles consist of a mat covered with asphalt. A layer of gravel pressed into the asphalt gives the shingle its color and provides protection from ultraviolet light.
The square covers approximately 100 square feet. Roofers install felt prior to installing the shingles. When installed, the shingles overlap, exposing slightly less than one half of the material. Installers offset the courses to ensure the row covers the seams between shingles on the row below it. Roofers sometimes install a second set of shingles over an existing set, but the weight of the shingles limits installation to two layers.