How Do Roofers Measure A Roof

November 1, 2021

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How Much Metal Roof Material Do You Need

How to Measure a Roof

Reviewed by Tomas Kalkys. President. Qualifications: More than 20 years of experience in residential and commercial exterior remodeling. Founding farther of Legacy Service. Written by LegacyUSA Team

posted on May 12, 2020

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Whether youre installing or replacing a metal roof, its a good idea to determine the amount of roofing material youll need for coverage. How to measure a roof for metal roofing installation can be accomplished in a variety of ways depending on the structure of your home. In this article, were going to provide you with a step-by-step guide to help you calculate the metal roofing materials needed for your house.

Here at Legacy Service, we provide metal roofing replacement and installation services. If youre interested in upgrading your homes exterior, please feel free to contact us by either giving us a call at 215-798-9790 or visiting . If youre interested in learning, How many sheets of metal roofing do I need for my home?, then continue reading.

Estimate The Length Of The Sheets

Once you know how many sheets you need, you will have to determine how long the sheets need to be. For this, make sure to measure all sides of the roof, as the peak and the base can have different measurements. If you prefer the metal to overhang slightly, make sure to add an inch or two to your measurement.

Calculating How Many Shingles You’ll Need

1Convert the area into roofing squares, the measurement used for materials. In roofing terms, a “square” is 100 square feet . Therefore, divide your total area by 100 to get the number of squares.XResearch source

So, for instance, if your total is 2,381 square feet, that’s approximately 23.8 squares or 24 squares, rounded up.

You can also use an app or a roofing calculator to decide how many shingles you’ll need.

If you’re in a country other than the U.S., check the size of roofing bundles in your area before making this calculation, as they can vary from country to country.

2Determine the number of shingle bundles you’ll need by multiplying by 3. Shingles typically come in a bundle that’s large enough to cover 1/3 of a square. To figure out how many bundles you’ll need, multiply the number of squares by 3.XResearch source

So if you have 24 squares, multiply that by 3 to get 72 bundles.

3Figure out the amount of roofing felt you’ll need by dividing by 2 or 4. Felt is what goes under the shingles. If you’re buying 15-pound felt, 1 roll will be enough for 4 squares. If you’re buying 30-pound felt, 1 roll will be enough for 2 squares. Divide your squares by one of these numbers to get the number of rolls you’ll need, depending on the thickness of felt you want.XResearch source

If you’re trying to cover 24 squares, divide by 4 for a 15-pound roll to get 6 rolls.

If you’re trying to cover 24 squares with a 30-pound roll, divide by 2 to get 12 rolls.

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Roof Pitch Angles: How To Calculate Your Roof Pitch

Understanding your new roof’s pitch and slope is incredibly important. This helps you understand how excess water, snow, or debris falls off the roof, which also helps guide you to the right type of shingles or roofing materials you need. We’re here to teach you how to easily calculate and estimate your roof pitch angles manually.

How Are Roofing Shingles Measured

Roof shingles are either sold by the bundle or the square. To measure the number of roofing shingles, you need to know the total sq. ft. of your roofs surface. The number of shingles to cover 100 sq. ft. of a roof is one square of shingles. On average, a square is three bundles of roofing shingles.

There are 29 shingles with measurements of 12 in. by 36 in. in each bundle when in three bundles per square. To determine how many bundles a client needs to order is to calculate the roof area. This is done by measuring the width to the length of your house. When the roof area is calculated, additional shingles will be added to account for waste and backup shingles.

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Easy Mode: How To Measure A Roof With Google Earth

Roof Online Staff

18. Done!

Keep in mind that this measuring technique is only usefully accurate for low-slope or flat roofs, and satellite images will not help you find the pitch of a roof.

If you want to measure a roof with a pitched roof, first see How to Find the Area of a Sloped Roof.

And even flat roofs usually have a little bit of a slope, so you might want to use a roof pitch multiplier once you have your area figured out.

What If You Have A Steep Roof

To measure a steep roof, use one of the following alternate methods:

Method 1

Calculate the roof length by measuring the exterior walls plus the overhang for the length of the house parallel to the ridge.

Next, throw a rope over the ridge and mark it where it meets each eave. This will give the width dimension to use in figuring your area. This should be done on each roof section containing a horizontal ridge.

Method 2

Determine the roof area by using a mathematical formula that accounts for the roof length, total span, and roof pitch:

Determine your roof pitch by using a pitch gauge or a smartphone app .

Measure the length of the roof surface, including overhangs.

Measure the span of the roof, including overhangs.

Multiply the length x the span. The result will be the plane area. Use the chart below to calculate the total area of the roof.

Calculate the total roof area Plane Area x Correction Factor = Roof Area

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Roof Size And Roofing Materials

Of course, the real reason why you are calculating the roof area is because you need roofing materials. In most cases, this is shingles. But it could also be slate tiles or a metal material. All roofing materials are calculated in terms of squares, and not square feet.

The roofing and construction industry has determined that one roof square = 100 square feet.

Thus, if you measure the roof at 500 square feet, that translates into 5 roofing squares. When you go to your local home improvement store, that is the number that you need to focus on, not the actual dimensions of your roof.

This should make intuitive sense, especially if you have a complex roof with many different slopes, angles, hips and valleys.

Just one important point to keep in mind here you will want to build in a small amount of overage when you measure and purchase roofing supplies.

As a general rule of thumb, that amount is 10% for a traditional gable roof and 15-20% for a more complex roof shape . You dont want to over-estimate too much, though, otherwise your bill is going to be entirely too high!

Squares Rectangles And Triangles

How to measure a roof for shingles

Nearly every roof, no matter how simple or complicated, can be broken down into squares, rectangles or triangles. You can draw lines on your diagram from the ridge to the eaves to make triangles out of the hips. This will leave you with four triangles for the hips, two rectangles for the rest of the hip roof, and another rectangle for the lean-to roof.

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How To Measure A Flat Roof Accurately

When you begin any roofing project, making accurate measurements is a necessity, to avoid buying the wrong quantities of materials.

When these types of mistakes are made, it can lead to overbuying or underbuying and neither scenario is a good one in roofing.

It is therefore critical to ensure you measure your flat roof accurately, and once you are satisfied you have the right measurements, go ahead and measure again to be absolutely sure!

You could also have another person measure too, just to be certain.So, how do you measure a flat roof accurately? It really isnt that difficult once you know how

Using a long measuring tape, carefully measure the full length of the structure from the outside of the building. Then measure the full width.NOTE: you dont have to be on the flat roof to do this accurately, you can measure on the ground.

Measure from outside the building to give an accurate representation. Depending on the thickness of your walls, measuring from the inside could give you a false measurement that is too small.

Once you have your two accurate measurements, you are ready to move on to calculating the size of membrane you will need.

So What Is A Roofing Square

A roofing square is a measurement, but it has nothing to do with square feet, meters, yards, or miles. A roofing square is commonly used by roofing companies and is roughly equivalent to 100 square feet. This measurement does not change whether it is a square of shingles or a square of tarp. This is because roofing squares are used to make calculating the cost of materials and labor easier than if you had to use square feet or yards.

Figure Out Your Homes Footprint

If you use the square footage of your home, youll only get a vague idea of what the square footage of your roof is. Thats why you have to figure out your homes footprint.

A person of average height will have a stride somewhere between 2 to 2.5 feet. To figure out your homes footprint, you can step off the dimensions of your roof by counting the steps you take to get the length of your home. You will then step off the width of your home.

After stepping off the length and width of your home, youll multiply the two numbers to get your homes footprint.

Length x width = your home’s footprint

Your calculations are going to be off, but measuring this way can give you a basic idea of your homes footprint. Keep in mind, square footage of a house does not equal the square footage of a roof.

How To Calculate Your Roof Pitch On The Roof

If you’d like to calculate your pitched roof manually for an exact measurement and aren’t afraid of heights, whip out the tape measure and spirit level, and carefully climb the ladder to access your roof. Whether you have an asphalt shingle roof, rubber membrane, or metal roof, always make sure it’s safe to stand on your roof first.

Once you’re safely on your roof, measure 1-foot up from the base, which will give you the run. Then place the spirit level at the 1-foot marker, and once it is even, measure from the bottom of the level to the top of your roof. This will give you the rise.

For example, if your rise is 6 inches, then your roof pitch will be 6/12. For every 12 inches of horizontal run, the roof rises 6 inches.

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How To Measure A Flat Roof

When measuring a roof like the one illustrated above you are going to need to divide it into rectangles as we did in Image 1.2. You will then calculate the area of the rectangles and add them together. This is known as the positive roof measuring method. So you will find the area of section A, B, & C, and the add them together to get the area of the entire roof. To find the area of a level rectangle you will multiply the length by the width.

Area of a level rectangle = Length x Width

Example 1.1

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What Else Impacts The Cost Of Your New Roof

Now you know how to roughly calculate your roofs square footage and 3 more factors that impact the cost. Remember, the only way to get a 100 percent accurate measurement is to have a local roofing contractor come out to professionally measure your roof.

Knowing your square footage and the 3 other cost factors lays the groundwork for learning the size of your roof investment. However, there are even more factors that impact the cost of your new roof besides whats listed in this article.

To understand where your hard-earned money is going when you invest in a new roof, we broke down the 9 factors that affect the cost of your new roof.

The team at Bill Ragan Roofing has provided high-quality roofing services in the Nashville area since 1990. We give you an experience rare in the roofing industry with our workmanship and customer service.Thats why were proud to offer you a lifetime warranty.

Measuring Your Roof Account For Roof Penetrations

How to measure a roof for shingles

Oh, and dont forget to list pipe sizes for boots, and dimensions for any skylights, chimneys or other roof penetrations on your sketch.From there, our Measuring and Estimating Guide will show you how to calculate the list of materials needed. If youre not comfortable with completing that yourself, no problem. Just give us a call at any of our locations and we will be happy to help you out.

Total Square Footage Vs Number Of Squares

The number of roofing squares is simple enough to calculate in standard gable roofs. In many cases, all a roofing contractor needs to do to find out the pitch of your roof is measure the length and width of each plane, which form two sides of a triangle. The third side, the roof slope, is easy to find by using the Pythagorean Theorem.

However, some roofs have an intricate mansard or gambrel design that includes ridges, turns, and valleys, not just a plain sloping roof deck. In such projects, calculating the number of roof squares may be more complicated.

How Many Bundles Of Shingles Per Square

A package of roofing shingles is called a bundle. Laminate or architectural shingles, one of the most common types of roofing shingles, are generally packaged in three bundles per square.

So in the 2400 square foot gable roof example, you would need 72 bundles of shingles .

Here are a couple more examples:

How To Measure The Perimeter Of A Sloped Roof

The perimeter of a hip roof or a hip and valley roof run horizontally to the ground. Take a look at image 1.16 and image 1.17 for a visual example for better understanding. You can determine the length and width by simply using the dimensions from the roof plan. Therefore, you can find the perimeter of a hip roof or a hip and gable roof by using the same formula used to find the perimeter of a flat roof.

Perimeter = 2

If the building has no recesses the the formula is:

Perimeter = 2

Find the perimeter of the roof in image 1.15

Perimeter = 2 = 110 linear feet.

When you are trying to find the perimeter of a gable roof you must also factor in the slope of the gable. Since the gable edge runs diagonal from the ground the plan length is not the actual length. If you were to use the plan length to determine the perimeter of a gable roof your measurements would be short resulting in underestimating the materials needed such as eaves drip, rafters, and fascia board. To find the perimeter of a gable roof your formula is:

Perimeter of Gable Roof = 2

Actual Width =

Thus, the formula for the Perimeter of a Gable roof is:

Perimeter = 2)

Calculating The Area From The Building’s Square Footage

1Find the square footage or square meterage of your home. You’ll need this information to estimate the area of your roof. You can find this information online on real estate websites or on your house or building title.XResearch source

Keep in mind that this estimation won’t include any areas like garages or enclosed patios that the roof covers. You may need to measure these rooms by hand to figure out the area.

To figure out the area of a square or rectangular room, measure length and width and multiply them together to get the area. Add that to your square footage total.

2Measure the pitch of your roof in the attic. Mark a length of 1 foot on a long level, starting from one end. Hold the end you measured from against the bottom of a rafter so it’s sticking straight out horizontally and is level. From the 1 ft spot you marked on the level, measure upward to the rafter. The number is the first part of the pitch, while “12 inches” is the second part of the pitch. So if you measured a “5” going up, the pitch is 5/12, or 5 inches every 1 foot.XResearch source

You’re basically making a triangle. The level and measuring tape will make a right angle, while the rafter will be the hypotenuse of the triangle.

Most roofing calculators will accept this measurement as is, such as 5/12.

The pitch is important because it increases the area of the roof by stretching out the height.

For example, the slope factor for 5/12 is 1.08.

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Measuring For Metal Roofing Measurements You Will Need

Then, to successfully complete your sketch, do your best and get the following measurements covered:Start with the panel lengths measure the panel length from the eave to ridge for each different eave-to-ridge distance.Then, get your width measurements the width measurements parallel to the ridge or eave will help you determine the number of 3 panelsYoull also need to cover the slope. So be sure to note the roof pitch in each section and indicate the down slope direction with an arrow on your drawing.