Measure a Roof

You may find relief in knowing there are several different methods to measuring a roof. If the roof is very steep or if you are not one for heights or climbing ladders, you can choose to measure your roof from the ground. Though this measurement will not be quite as precise as if you got on the roof and measured each section exactly, a roof measurement from the ground will provide you with numbers close enough to get a fairly accurate estimate. You still may need a ladder, but you will not have to get all the way on top the roof.

Steps

Diagram roof measurement

  1. Draw a diagram of your roof on a piece of paper. Label each section of the roof. You will write your measurements on the diagram to make it easy to make the roof's size calculations. Being able to see where you have been and what you have already measured will help make the process go more quickly.
  2. Find the area of triangular sections. This is not as difficult as you might think. The area of a triangle is half the length times the width (L x W / 2). Use a tape measure to measure the length of the eave and the length from the center of the eave to the opposite point. Multiply these two numbers together and divide by 2. Mark this number on your diagram as the square feet for this section.
  3. Determine the square feet of rectangle-shaped sections. Use the measuring tape to measure the length and the width of the squared off sections. Multiply these two numbers together, and that is the square-feet total you will mark on your diagram.
  4. Get the total square feet. Add up the square feet you determined for each section. The sum of these numbers is your total square feet of the roof.
  5. Calculate the amount of materials you will need. Roofing materials are determined based on the number of "square" a roof is, not the number of square feet. To calculate the square of a roof, take the number of square feet and divide it by 100.

Remote measurement services

  1. Research an online option. Since 2007 roof measurements have been available from multiple online services. These services utilize satellite and/or aerial imagery to measure roofs wherever they have image coverage. These services are able to achieve their measurements remotely from computers and deliver their roof measurements via email for a small fee.
  2. Once you receive your measurements be sure to add additional material for waste. Waste is dependent on the complexity of your roof and how you decide to roof your valleys (there are 3 methods of roofing a valley). Check out How to Estimate Roofing Materials for more help on these calculations.

Roof measurement from the ground

  1. Measure the four sides of the house from the ground using a measuring tape. Be sure to add estimated measurements into each side's total to account for the overhangs. Mark these measurements on your diagram.
  2. Get the total square feet. Add up the square feet you determined for each section. The sum of these numbers if your total square feet of the house, not the roof.
  3. Calculate the number of squares the house is. To calculate the square of a roof, take the number of square feet and divide it by 100.
  4. Determine the pitch of the roof. The pitch is how steep the roof is. Pitch is calculated by the roof's rise over its run. Measure from the edge of the roof over 12 inches (12 is the run) and see how many inches up the roof line is (this is the rise). Get a slope multiplier from the chart below. Roof Pitch Slope Multiplier Chart: 2 in 12 = 1.102, 3 in 12 = 1.134, 4 in 12 = 1.159, 5 in 12 = 1.191, 6 in 12 = 1.230, 7 in 12 = 1.274, 8 in 12 = 1.322, 9 in 12 = 1.375, 10 in 12 = 1.432, 11 in 12 = 1.493, 12 in 12 = 1.554.
  5. Get the final roof calculation. Take the ground level square figure you came up with and multiply it by the appropriate slope multiplier. This will give you your roof square.

Simple rough measurement

This is not an extremely accurate method but works quite well to generate an idea on the size of your roof, very close, including data you may not have in hand like pitch, the size of your garage etc. It helps a rough but close number.

  1. Take into consideration the living space of your floor plan. Let's say this is roughly 2000 sq/ft.
  2. If your home is one story, add 1000 sq ft. You will be close. In the example of 2000 sq/ft, you may have like 3000 sq ft of roof, or 30 squares as most roofers call them (1 square = 100 sq. ft).
  3. If it is two stories, multiply your house floor plan by 1.3. In the case mentioned before, your home could be like 2600 sq ft, or 26 squares. Again you will be very close.

Things You'll Need

  • Ladder
  • Paper
  • Writing utensil
  • Measuring tape

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Sources and Citations

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