How to Calculate Roof Cost Basis

Calculating a cost basis for a flat roof is straightforward. Flat roofs are most commonly the roofs that are coated. These roofs are made up of underlayment and roll roofing. After the roll roofing is cemented in place, the roof is coated with roof sealer. This roof sealer comes in five-gallon buckets and is applied directly on top of the roll roofing. The cost of coating a roof will depend on the total square footage of the roof.

Things You'll Need

• Tape measure
• Ladder
• Calculator

Instructions

1. Climb a ladder to the roof and carefully step onto the flat surface. Run a tape measure across the width of the roof at both the top and bottom to verify the measurements are the same. Run the tape measure vertically along the length of the roof at two separate spots and record all the measurements.

2. Multiply the larger of the two recorded measurements for both the width and the length together to get the total square footage of the roof. Figure how much No. 15 felt underlayment will be needed by dividing that number by 432, the number of square feet in a roll of underlayment.

3. Determine how many five-gallon buckets of roofing sealer will be needed for installation. Each bucket will cover about 400 square feet. Divide the total square footage of the roof by 400 to get the number of buckets for one coat. Double that number to get the number of buckets needed for two coats.

4. Divide the total square footage by 200 for the roll roofing, which comes in 200-square-foot rolls. Figure in for other materials, such as staples for the underlayment and roofing cement for the roll roofing. Add the price of a 25-pound box of roofing nails and a trowel to spread out the roofing cement. You will also need a nail gun to secure the roll roofing and a pry bar to remove the old roof. Add up the costs of all tools and materials to get the final cost of a roof.

References

• Elastek: Frequently Asked Questions