Area of a rectangle or square:
A = L x W
Area = Length x Width
Example: 20 feet x 10 feet = 200 square feet
Area of a trapezoid:
A = [(B1 + B2) x H] / 2
Area = [(Top + Bottom) x Height] / 2
Example: [(5 feet + 10 feet) x 6 feet] / 2 = 45 square feet
Area of a triangle:
A = (B x H) / 2
Area = (Base x Height) / 2
Example: (5 feet x 4 feet) / 2 = 10 square feet
When you have finished calculating the area of each plane, use this information to find your roof’s total square footage. Add the area of each plane together, and the sum will be the total square footage of the roof.
The Drip Cap
- Before you do any roofing work, you must calculate the roof’s square footage to determine how much material you need.
- Calculate each plane separately.
- For example, if a triangle-shaped roof plane measures 60 feet along the base and is 30 feet high, we have 60 x 30 = 1,800 feet, divided by 2 = 900 square feet for the triangle-shaped plane.
- The square footage would be 40 x 40 = 1,600 square feet (the square) plus 20 x 40 = 800 / 2 = 400 square feet (the triangle).