How to Measure a Roof- 4 Ways to Find out the Numbers

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measuring tape rolled out on three lines

There a few reasons you might need to have accurate measurements of a roof. It could be time to replace the roofing material, you may be considering how much space you have for solar panels, or you might simply want to know.

Regardless of why you need these measurements, there are different ways to learn how to measure a roof. Some are simple, yet they provide only rough estimates. Other methods can get right down to fractions of an inch. Here are 4 ways on how to measure a roof to find out the numbers.

The Blueprint

Of course, you can always revert to the blueprints of your home or the building you need roof measurements. This method depends on a couple of factors though. There cannot have been any changes made to the roof, and you must trust that the blueprint measurements are accurate.

The other problem that often arises is that there isn’t a blueprint. Some of these works might not include measurements for every section of your roof. There might be an overall number yet nothing that designates the dimensions of every individual section.

The crudest way to calculate roof dimensions is to simply take the square footage estimated for the home or building and add 1,000 square feet. This method may work in some instances. Nonetheless, when calculating for roofing materials, you are going to produce a lot of waste. For two-story homes, multiply the final number by 1.3.

If you have a blueprint with good roof measurements, consider yourself lucky. If not, there are other ways to learn how to measure a roof. Sometimes, house plans include the numbers for walls and overall square footage, but not for the individual sections of roof. Here are ways to get those numbers and be far more precise.

roof blueprint

Diagram from the Ground

Another alternative for how to measure a roof is to draw a diagram. This begins with a simple piece of blank paper and a pencil. If you aren’t skilled at drawing straight lines freehand, you might want to include a ruler. Try to be neat since you use this diagram to record your roof measurements.

You are going to measure the dimensions of the structure on the ground first. Each wall will correlate to a measurement of the roof. Write these numbers on a piece of scratch paper so you can transfer them to your diagram. Hip roofs are going to have a triangle or raised pitch at each end. You only need the measurement for the height of this triangle.

To get the square foot measurement, necessary for how to measure a roof using this method, you multiply the length times the width and divide by 2. (LxW/2) is the formula. Note down the result of this calculation on your diagram.

Take your ground measurements and use these to measure the square footage of the actual roof sections. Be sure to include the length of roof overhang. This number will be added to the (w) width measurement on your diagram. Take the square foot measurement for each section, including the triangle-shaped sides and multiply them together.

Physically Measure the Roof

man measuring the size of the white roof with ruler

When thinking about how to measure a roof, the best method is the most difficult. It involves climbing up on your roof. As precise as it will be, before you attempt this method, assess your ability to physically handle the job. It will involve climbing atop your roof, and safely take precise measurements. Frequently, this job is best left to a roofing professional.

If you think you can handle the physical aspect of this method, here is how to measure a roof from atop the roof itself. You are going to need a tape measure that is long enough to span the longest part of the roof. Usually, having both a handheld 25-foot tape and a 100-foot is recommended.

You can use a piece of sidewalk chalk to write numbers on the roof as you go. It will wash off after a couple of rains. Measure each roof section and write down those numbers. Just as you did with your ground diagram, write these measurements on a separate piece of paper when you finish.

Use the same length times width formula to calculate the square footage for each individual section of roof. You can use an online Roofing Material Calculator to do the math for you. This is you can learn how to measure a roof by actually climbing on the roof. It is more difficult, but you can usually count on these numbers being 100% accurate.

Online Computerized Measurements

This method for how to measure a roof has only been around for about a decade. Starting in 2007, roof measurements have been obtainable from different sources. The measurements for any roof visible from space are available using satellites.

Mind you! These services will give you precise roof dimensions but only for a cost. While there is a fee associated with this manner of how to measure a roof, it is regarded as the most accurate way other than climbing on top the roof itself. It is a lot safer as well. Many of these roofing measurement services such as EagleView offer different levels of accuracy. This dictates how much you have to pay.

Be aware that if you are going to use the satellite method of how to measure a roof, you might as well be pinpoint accurate. One positive aspect of this method is that you will never have to do it again if you keep a record of the data.

In Conclusion

These four techniques address how to measure a roof. You can quickly translate these numbers for the purpose of purchasing materials to put a new roof on a structure. All you have to do is take your final square footage calculations and divide by 100.

If all you want to do is estimate the total square footage of your roof such as calculating for gutter size, you can employ either of the first two methods. When you want to figure out the necessary roofing materials accurately, the last two options are the best alternative. If you have any questions about your accuracy, consult with a roofing professional.

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