Determining Roof Area For Shingles

You may occasionally need to purchase roof shingles for a repair project or to re-roof your home. Roof shingles come in various styles and shapes, but the basic calculations to determine roof area are the same.

Shingles and Roofing Materials

Shingles come in bundles of 3 which equal a square. Each square represents 100 square feet of roof area. When making calculations to determine how many shingles to purchase, keep in mind that you will not only need enough for the correct square footage, but you will also need 10 to 15 percent more shingles to accommodate dips and valleys in your roof or for extra coverage.

Additionally, you will need to purchase:

  • Roof ridge shingles
  • Drip edge
  • Hip and ridge vent
  • Asphalt paper
  • Flashing
  • Roofing nails.

Asphalt paper and flashing are sold in rolls. You will need enough asphalt paper to place under all of the shingles for your entire roof area. Flashing usually comes in 16-inch wide rolls or 6x6 or 8x8 square inch steps. Step flashing is used around chimneys, doorways and at the points where side walls come together.

Hip and ridge vent requirements vary according to local building codes.

Be sure to purchase all of your roofing materials in advance of starting the project. Also, keep in mind that roofing materials are run in batches that have variations in quality and color. If roof shingle bundles are purchased in differing lots, it may result in inconsistencies that lead to leaks and other defects in the roof.

Roof Measurements

  1. Measure each plane of your roof by length and width. Multiply these two measurements together and you will have the square footage of each roof plane. Include every roof plane on the roof, even if it is a small area.
    Add all of the roof plane square footage measurements together to calculate the entire area of the roof.
  2. Divide this number by 100 to determine how many squares you have in your roof area.
  3. Add 10 percent for any overage that might be needed when installing the shingles.
  4. Divide the total number by 3, and you will know how many bundles you need to purchase for your roofing project.

Ridge Caps

Every bundle of shingles equals 35 linear feet of ridge caps. Ridge caps are the shingles that go along the supporting roof ridge beam.

To determine the amount of linear feet in your roof, measure all of the roof ridges on your roof and add them together. This will give you the entire roof ridge measurement. Now divide that number by 35 and you will have the number of ridge cap shingle bundles you need to purchase.

Hip and Ridge Vent

Measure the length of the roof hip and ridges. Multiply this number by 75 percent and you will have the amount of vent needed for your roof area.