Estimate Guide for Roofing

Area

• Estimates start with the basic area of a roof. Multiply the length and width of your home. For example, a structure that is 25-by-80 feet has a basic area of 2,000 square feet. You then determine the pitch or slope of a roof by estimating the number of feet it rises over the number of feet it moves forward. A low-pitched roof rises 5 feet for every 12, or has a pitch no greater than 5:12. A medium-pitched roof goes from 5:12 to 9:12, and a steep pitch goes from 5:12 to 10:12.

Multiplier

• The pitch determines the roof multiplier, which you multiply by the base square feet to calculate the square foot of the surface. Use a roofing multiplier from 1.15 to 1.25 for low pitches, from 1.25 to 1.4 for medium pitches and from 1.41 to 1.75 for steep pitches. For example, a 2,000-square-foot roof with a medium pitch could use a 1.3 multiplier. Multiplying 2,000 by 1.3 produces 2,600, which is the number of square feet you can use to estimate costs.

Costs

• According to Cost Owl, with prices accurate at the time of publication, a shake roof costs from $2 to $3.25 per square foot installed, putting the cost of a 2,600-square-foot at between $5,200 and $8,450. An asphalt roof runs from $1.75 to $2.50 per square foot installed, making the example roof cost about $4,550 to $6,500. A metal roof costs $4 to $5 a square foot installed, so the example runs $10,400 to $13,000. A natural slate is priced at $25 to $35 installed, so the total for the example becomes $65,000 to $91,000.

Labor

• Labor costs vary across the country, so the location of a roofing project affects the estimated cost. The Bureau of Labor Statistics shows mean wages of roofers at $18.21 per hour for a three-year period from November 2007 through May 2010, with the lowest 10 percent earning $10.59 per hour and the highest 10 percent receiving $29.14 per hour. The highest wages were in Hawaii at a mean $26.20 per hour, Connecticut at a mean $26.08 per hour and Minnesota at a mean $24.81 per hour. Lower-than-average rates were available in New Mexico at a mean $14.11 per hour, Arizona at a mean $15.25 per hour and Florida at a mean $15.36 per hour.