How to calculate roofing materials

Written by anne mullenniex Google
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How to calculate roofing materials
Take precise measurements of roof sides to estimate squares of shingles needed for your roofing project. (tape measure image by Joann Cooper from

Organising a roofing project begins with a materials list. Follow this with careful measurements of your roof to determine the amounts needed of the items on your list.

Skill level:

Things you need

  • Tape measure
  • Paper
  • Pencil
  • Calculator
  • Ladder

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  1. 1

    Look at your roof in terms of squares, rectangles and triangles. Roof sides are separated from each other either by ridges or angles--figure out the shapes of each side of your roof and take measurements accordingly. Multiply the length (L) in feet by the height (H) of square or rectangular sides to compute the area in square feet (sf). Triangular portions of a roof--caused by adjacent roof sides meeting at an angle--can be computed by multiplying the ridge length by the height of the side, divided in half.

  2. 2

    Add together the area of all the sides, and then add 10 to 15 per cent to account for waste. Compute the number of squares of shingles needed by dividing the total area by 100 sf.

  3. 3

    Use the individual roof side areas divided by 250 sf to figure out how many roof vents are needed for each side.

  4. 4

    Use the total area of the roof to figure out how many rolls of felt underlayment you will need. Each roll of felt paper lists its total square foot of coverage on the package. Divide this number into the total area of the roof for the number of rolls of felt to order.

  5. 5

    Multiply the number of squares of roofing shingles needed by 2 or 2.5 for the number of pounds of roofing nails you should buy.

  6. 6

    Add together the linear "perimeter" measurements of every roof side along the fascia board to calculate total linear feet of metal drip edge.

  7. 7

    Measure around chimneys, along cupolas and gables, and down valleys formed along the joint of adjacent roof sides meeting at ninety degree angles. Add two feet to the valley measurements to account for ridge overlap and scrap. Total all of these measurements for the total linear feet of metal flashing needed.

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