Roofing Cost Calculator

Roofing is priced in squares, the trade unit equal to 100 square feet, because shingles are packaged and sold that way, typically three bundles to the square. Pitch enters twice. Geometrically, the sloped surface exceeds the horizontal footprint by a factor of the square root of one plus the square of rise over run, so a 6/12 roof has about 1.118 times the plan area and a 12/12 roof about 1.414 times. Pitch also raises labor, because anything steeper than roughly 6/12 requires roof jacks, staging, and fall protection under OSHA rules that apply above six feet. Material price spans a wide band per square, from three-tab asphalt through architectural laminates, standing-seam metal, and tile, up to natural slate, and service life scales with it from roughly 25 years for asphalt to a century for slate. The rest of the estimate is site work. Tear-off and disposal scale with the number of existing layers; the International Residential Code allows at most two applications of asphalt shingles before a complete strip is mandatory, and old layers hide deck damage that appears only once removed. Underlayment, drip edge, valley and step flashing, ridge cap, and in cold regions an ice barrier along the eaves are separate lines. Attic ventilation is code-driven rather than optional: the usual requirement is one square foot of net free vent area per 150 square feet of attic, relaxed to 1 in 300 when intake and exhaust are balanced and a vapor retarder is present. Overhead and profit near 12 percent, permits, and dumpster fees complete the total.

Slate and fired clay tile roofs are centuries old, and industrial-scale slate quarrying in north Wales during the eighteenth and nineteenth centuries made thin, uniform slate cheap enough to ship worldwide, which is why so much Victorian housing carries it. The modern low-cost roof, however, began with coal-tar and asphalt built-up roofing in the mid-nineteenth century and with saturated felt roll roofing sold by the roll. The individual asphalt shingle followed when Henry M. Reynolds of Grand Rapids, Michigan began cutting roll roofing into separate rectangular units around 1903 and advertised a roof that would last as long as the house; the format spread quickly because it could be nailed by unskilled labor. Asphalt shingles were built on organic felt mats until fiberglass mats displaced them through the 1980s, improving fire performance and dimensional stability. Testing standards followed the product: ASTM D3462 governs fiberglass asphalt shingles, ASTM D7158 assigns wind classifications of D, G, and H corresponding to 90, 120, and 150 miles per hour, and fire classifications of A, B, and C come from ASTM E108 and the equivalent UL 790 test. Roll-formed standing-seam metal roofing became a mainstream residential option in the late twentieth century as coil coating improved corrosion resistance. Pricing conventions proved more stable than the products; the square as a unit dates to the era when roofing was first sold in prepackaged bundles rather than made on site.