As a homeowner, it is important to know how much a contractor may charge for the repair or replacement of the roof of a home. An owner should know how to measure the size of the roof as well as the length of the valleys, dormers, and ridge vents to compare against any estimates that are received.

Armed with the knowledge about basic measurements, a homeowner can approximate the amount of material needed for the replacing of a roof. That knowledge can save a homeowner from the result of a miscalculation as anyone can make mistakes when calculating an estimate, even expert contractors. Knowing this simple calculation result, a homeowner can correct a contractor on the spot if there are any major discrepancies on the square footage of the roofing area.

Basic Mathematics

When measuring the roof, the result is expressed in ‘squares’. In geometry, one square is equivalent to one hundred square feet (1 = 100 square feet). So, to determine the area of a triangle, this simple geometrical equation must be remembered: area is equivalent to the length of the base times the height of the triangle in feet divided by two. The equation should look like this; (b x h)/2. For example, 40-foot (h) x 40-foot (b) divided by 2 is 40 x 40 divided by 2 equals 800 sq. feet or 8 squares.

In order to get the correct estimated measurement of the house-top, one needs to have an aerial view or rough sketch of the roof and divide it into different sections.

Step 1: Measuring Overall Area

One must first draw a diagram of the house-top. A person must get a 100-foot measuring tape, a pencil, some paper and an assistant. The assistant will hold the tip of the measuring tape while the homeowner checks and records the measurements. The sketch should include the ridge, valleys, dormers, vents, chimneys and pipes. Begin at one corner on a side and measure the dimension of the exterior walls, measuring both width and length. Most roofs have an area that extends out to cover and protect exterior walls and side known as overhangs. The overhang must be measured and added to the completed dimensions. Then the measurement should be transposed onto the diagram.

Step 2: Measuring the Pitch

The pitch is basically the steepness of a roof and is measured by determining the rise in inches per every 12 inches of horizontal length. To arrive at a multiplier that will figure into the calculations, pitch can be divided into 3 categories: low, medium and high. Low pitch is a roof that can easily be walked and the multiplier would be 1.15 to 1.25. Medium would be a rise of 5 to 9 feet for every 12 inches and would result in a multiplier of 1.25 to 1.4. The high or steep slope category covers a rise that is greater than 9 feet for every 12 inches and gives a multiplier of 1.7 and higher.

Step 3: Final Computation

After getting the dimensions, roof pitch and multiplier, the size of a home’s house-top can be calculated. Take the computed overall area in square feet and multiply it by the pitch multiplier. For example, the ground dimension is equivalent to 1,104 square feet and the roof pitch is low at 1.15. The resulting equation should look like: 1,104 x 1.15 = 1,270 sq. feet. Therefore, the estimated amount of material needed for the roof is 12.7 squares. It can also be calculated by looking at the original square footage of 1,104 or 11 squares x 1.15 = 12.65. Either calculation represents the ‘estimated’ squares needed for the replacement job.

Knowing how to measure a roof can give a homeowner the ability to make sure any estimate given by a contractor is very accurate – and this can calculate into a large monetary savings. So learn the right way to measure that house-top and translate that information into accurate replacement cost!