Whether your seeing too many leaks, a bad storm did damage, or your shingles are just wearing past their prime, there comes a time when your roof needs a replacement to keep your house adequately protected from the elements. This is a process most homeowners dread both because of the stress and the expense, but doing your homework and investing some time into getting an accurate idea of your roof’s square footage can significantly aid in lowering both. This is because getting the right measurements ensures you get the right price in terms of labor and material purchase so that there are no extras or waste in the roofing process.
So get out your measuring tape and the pen and paper. It’s time to measure your roof!
Roofing Units and Measurement
The concept of measuring your roof is really rather simple, you need to map out all the surface areas on the roof and add them together for a final total. Roofs are measured in what are called squares. Squares are areas of 100 sq feet and are used to purchase materials like tiles or shingles for the laying of the roof. To arrive at this number, simply divide the total roof surface area you find by 100 and you will have the amount of roof squares on your home.
But first you need to find the surface area, and this is done by multiplying the length of the roof eave (including overhangs) by the length of the roof’s pitch.
To calculate roof pitch you can either physically measure it with tape or use the Pythagorean theorem to find it by plugging in the height and width of your gable’s triangular section to find the hypotenuse (the pitch length).
This process needs to be done for every roof surface, including dormers. The more surfaces, the more math, but the process of finding and adding surface areas together remains the same for all roofs.
Measuring is done differently for different roof shapes:
Measuring Gabled Roofs and Sheds
Gabled roofs are the easiest to measure because the planar surfaces they create are square. All you need to do is find the length of the eave and the pitch, multiply, and you’re done.
Eave Length X Pitch Length = Gabled Roof Surface Area
Remember to add both sides of the gable to the final calculation. For sheds or lean-to roofs, there will be only one side to calculate.
Measuring Square-Hipped Roofs
Hipped roofs are a bit more complicated to measure because the roofline is sloped inward with the pitch.
For a totally hipped roof with all surfaces meeting at a single point, the calculation is still pretty simple and just involves multiplying the length of the eave and the pitch, before dividing the result by two.
(Eave Length X Pitch Length) / 2 = Square Hipped Roof Area
Don’t forget to add up the four sides.
Measuring Rectangular-Hipped Roofs
For hipped roofs with apex points separated by a ridge, you have to change the math a little. Add the length of the ridge at the top to the length of the eave at the bottom and then multiply this result by the length of the pitch, before finally dividing by two. Mansard roofs are calculated the same way for those areas of them which are shingled.
<(Ridge Length + Eave Length) X Pitch Length>/ 2 = Rectangular Hipped Roof Area
How to Tackle Complex Roofs
Not all roofs are so simple and many have a complex arrangement of different pitches and lengths which come together to create valleys and irregular planar surfaces to calculate. If you are faced with such a roof it is helpful to make a plan sketch to see the shapes and then divide them up into simple rectangular and triangular sections for easier math.
When your done with the calculator, the process is the same: add all the surfaces together and divide by 100 to convert the surface area into roofing square units.