## Determine Roof Pitch And Slope Factor

The pitch of your roof can dramatically increase its surface area, so its important to take it into account in your estimation. Simply use a 12-inch level to measure how many inches it rises for per foot it runs. This can help you determine your roofs slope factor. You can use pre-made tables online, or you can calculate it yourself. Simply square the rise and run of your roofs slope, add them together, then find their square root and divide it by 12.

In this case, lets assume your roof has a pitch of 3/12, which means for every twelve inches of length, it will rise by two. Your roofs slope factor would then be equal to ) / 12 in, or 1.03078. Most tables will round this to 1.03.

## How To Figure Out The Square Footage Of A Roof

Repairing or replacing your roof can be expensive, especially if you dont know how to calculate its square footage. A wrong estimate can cost you thousands of dollars and might even delay your roof repair, leaving your home exposed to the elements. The good news is you can easily estimate the square footage of your roof with a few tools and basic geometry.

## Calculate The Square Footage Of Your Roof

Now that you thought about the slope and complexity of your roof, youre ready to learn how to calculate the square footage of your roof.

To get a rough estimate for your roofs square footage, youll use this equation:

For example, if you have an easy up and over, walkable gable roof and a house that measures 56 feet lengthwise and 28 feet widthwise, your calculation will look like this:

1,568′ =

x 1.3

**2,038 = square feet of roof area**

**Using this equation wont be 100% accurate, but knowing your roofs square footage is a great jumping-off point to learn how much youll have to invest in your replacement.**

**Read Also: How Much Does A New Roof Cost In California **

## The Type Of Roof You Want

**The type of roof you want will have a big impact on the cost of your roof replacement.** There are a variety of different types of roofs for you to choose from based on your budget and the look you want.

If youre on a tight budget and looking for an affordable roof, an asphalt shingle roof might be right for you. But if youre looking to upgrade to a longer-lasting and sharp looking roof, theres the standing seam metal roof.

Asphalt and metal are two of the most commonly seen roof types, but there are also premium shingle roofs that come at a premium price. These roofs give you a unique look that really stands out. These premium roofs include cedar shake, slate, and tile.

The premium shingle roofs can get expensive quickly and be more than triple the cost of an asphalt shingle roof.

## The Negative Roof Measuring Method

To find the area of a roof using the negative roof measuring method you will extend the roof line past the roof to form a single rectangle. You will then subtract the rectangular areas that lie outside of the roof.

First you need to extend the roof lines to form a single rectangle.

**60 x 60 = 3600 sqft extended rectangle**

You then need need to find the area of the rectangles outside of the roof area. You can see in **Image 1.3 **that the areas outside the roof layout are sectioned off into section A and section B. We will find the areas of these sections and then subtract them from our extended rectangle.

**Area of section A = 20 x 20 = 400 sqft**

**Area of section B = 20 x 40 = 800 sqft**

The total area outside of the roof layout is 800 sqft + 400 sqft = 1200 sqft.

**3600 sqft 1200 sqft = 2400 sqft**

You can see that using the negative roof measurement method gives us the same result as the positive roof measurement method.

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## Plan For Extra Valley Material

Valleys are either woven or cut both methods require about the same number of shingles. On a woven valley, each course of shingles is extended beyond the valley crease and at least 12 in. onto the adjacent roof plane. Youll use 2 ft. of extra shingle material for each pair of woven courses. In the case of cut valleys, the shingles from the first roof plane thats shingled also extend onto the adjacent roof plane at least 12 in. just like woven valleys. Shingles from the next roof plane are cut just up from the valley line, and the cutoff pieces usually arent big enough to use elsewhere on the roof. Order two extra shingles per linear foot of valley to account for the overlaps and cutoffs. On a 16-ft. valley, you would need 32 shingles or roughly one extra bundle.

## Why Should I Measure My Own Roof

If you plan on re-roofing your own home then you will need to calculate materials so you wont waste your own time and money. If youre like most people, youll need to hire a professional.

Knowing your numbers will help you figure out what roofing materials are within your budget and having your square footage handy is a great way to protect yourself from inflated quotes.

**Also Check: Replacing Roof Trusses **

## How Many Squares Per Roll Of Underlayment

The roll size depends on the type of underlayment product. Synthetic underlayment comes in 10 square rolls, while regular #15 felt comes in 4 square rolls.

So for the 24 square roof example, you would need 2.4 rolls of synthetic underlayment, or 6 rolls of regular #15 felt.

- 24 squares ÷ 10 squares per roll = 2.4 rolls of synthetic underlayment
- 24 squares ÷ 4 squares per roll = 6 rolls of regular #15 felt

**Remember**: Add 10%-15% for the waste factor on underlayment, as well.

Finally, if you have any questions about your estimate, ask a roofing contractor in your area. Most will be happy to give you a free estimate.

## Hip And Ridge Cap Shingles

Hips and ridges are covered with cap shingles, which are 1-ft. shingle squares that wrap over the hip or ridge. Like regular shingles, they overlap for a 5-in. exposure.On roofs shingled with three-tab or no-cutout shingles, you simply cut standard shingles into caps. You can cap about 35 lin. ft. of ridge or hips with each bundle of three-tab shingles that come three bundles to the square. You can also salvage waste shingle pieces and portions of damaged shingles for use as caps.

For roofs shingled with laminated shingles, multi-cutout shingles, and other patterned shingles, youll have to order hip-and-ridge shingles that are manufactured as companions to the specific shingle product you are using. Theyre sold by the bundle and usually cap 35 lin. ft., but check with your supplier because some products vary. Just measure the length of the ridges and hips and divide by 35 to determine how many bundles of regular or hip-and-ridge shingles youll need.

**Recommended Reading: Corrugated Roofing Overhang **

## 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 Of A Complex Roof

Areas of complex roofs with multiple hips and valleys take the most time to calculate. Start by making a rough sketch of the roof. To simplify the calculation, break down the sketch into rectangles and right triangles , then take as many measurements of the roof as you can to match the sides of the rectangles and triangles on the sketch.

Use visual cues from the existing roof shingles or roof sheathing to determine square lines off eaves edges or ridges. These cues will help you measure the lengths of the sides of the rectangles and triangles. For instance, the cutout slots on shingled roofs run perpendicular to the eaves, and nail rows in sheathing are pretty close to square also. It is difficult sometimes to get accurate measurements. Dont get too concerned though just round lengths to the nearest 6 in.

With the sketch filled in with measurements, you can determine the size of the roof area. The area of a rectangle is length multiplied by width, whereas the area of a right triangle is the length of the two sides that meet at the 90-degree corner multiplied together and divided by two .

Tally the square footages of all the rectangles and triangles, which will give you the total square footage for the roof. The example here shows the calculation for a roof with two hips.

**Also Check: How To Extend A Metal Roof Overhang **

## How To Calculate A Roofing Square

Before beginning, make sure you can safely access your roofif you can’t, contact a roofing professional for help.

Grab your measuring tape, level, pen and paper, roof safety equipment, and your ladder. With these in hand, you can measure your roof in five simple steps.

**Determine the number of planes.**Your roof is made up of planes. If you have a flat roof, it has one plane. If you have a simple gable roof, it has two planes. The more architectural details your roof has, the more planes you will have to measure.

**Measure each plane**. Find the length and width of each plane. Then, multiply those two numbers together to find the square footage of that plane. For example, a 35 ft. X 36 ft. plane = 1260 sq. ft.

**Find the total of all the planes**. Add the square footage for each roof plane into one total. 1,260 sq. ft. + 1,260 sq. ft. = 2,520 sq. ft.

**Divide to find the squares.**To find how many squares are on your roof, divide the total square footage of all your planes by 100. In our example, the total was 25.2 squares 2,520 sq. ft. divided by 100.

**Remember the roof slope.**Roof slope indicates how steep your roof is and may increase the number of squares of materials you need. Roof slope is calculated by determining how many inches a roof rises vertically for every 12 inches it extends horizontally. For example, if that vertical rise is 4 inches, the slope is 4:12.

## How Many Extra Shingles Should You Buy

If you order shingles based solely on the area of the roof, you wont have enough. Youll need shingles for starter courses along the eaves and sometimes at rakes, and youll need shingles to cap hips and ridges. Cutting shingles also generates waste. In some places, including at the rakes, against walls and chimneys, and at valleys, youll need to cut shingles. Some of the cutoffs will be big enough to use as starter shingles or in other areas where cut shingles are needed, but smaller cutoffs will be waste.

**Read Also: New Roof Cost California **

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Below, there is a simple triangle, and the math used to work out how to make a proper measurement. Once you work through the basic triangle, we will review a typical roof, and how to apply some simple math to calculate how much material you will need for a roof used in our hypothetical example.

**1 roof square** = 100 square feet The length times the height of a triangle is twice its area . So if you divide your answer of a product of length times height by two, you will get the area of a triangle. /2 = Area

New Shingle Roof |

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In Figure above: l=30 feet h=12 feet /2 = 180 square feet

Now that the basic concept has been covered, lets take a look at a more complex roofing system. In this overhead view you see both a hip-end section, and gable ends. With a more complex roof such is this one, it is highly recommended that you make a basic sketch. By doing so, it will be easier to mark your measurements, and calculate the necessary materials for the project. For this example we will break this roof up into sections labeled A through E.

In the figure B. above, a sketched portion is a basic triangle. As we did in the first example, measure the length of the eaves, and the vertical line from the eaves half way point to the peak. Multiply these numbers, and then divide the answer by two./2 = 270 square feet

S1 = /2 = 135 square feetS2 = 50 × 15 = 750 square feetS3 = /2 = 135 square feet

## How To Calculate Your Roof Area

Knowing how to calculate your roof area can be a beneficial first step in estimating the cost of a new metal roof. In roofing we call the calculation of roofing materials needed a take-off.

A good roofing contractor will take the time make sure that the take-off is accurate. Proper measurements and attention to roof details ensure that material shortages are avoided and prevent overages .

**Also Check: How To Extend A Metal Roof Overhang **

## Find The Area Of A Roof

Multiply the length of the roof in feet by the width of the roof in feet to find the area of the roof in square feet. If you have multiple sections of roof find the area of each and add them together to find the total area.

If your roof is not flat and you cannot climb to the peak to get accurate width measurements then you can add a multiplier for the pitch of your roof.

Use our roof pitch calculator to find the pitch of your roof or find the pitch multiplier, then multiply the area of the footprint of your roof by the multiplier to find the actual area.

Alternatively, find the area of your roof using our roofing calculator, which can also estimate shingles and material needed for your project.

**Get Free Project Estimates**

Find Qualified Roofing Professionals in Your Area

**For example,** if your roof is 30 ft by 50 ft, then the area is 1,500 ft2.30 × 50 = 1,500 ft2

If your roof has triangles and other shapes youll need to use a calculator to find the square footage.

## How To Measure Your Total Roof Area

*Length x width = square footage*

In order to determine the amount of shingles you need for your roof, youll need to know the square footage of your roofs surface. Measurements for the area of the roof will depend on what roof type you may have, whether its a gable roof with fewer planes or a hip roof with more.

To find the square footage of your roof, measure the roof length and roof width of each plane, including overhangs, and multiply them together. Then, add up the square footage of each plane. This will give you the total square footage.

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## What Is Slope Factor

Taking a 2D measurement of a roof either online via Google Earth or by measuring the exterior walls of the home doesnt account for the elevation of the roof, which adds square footage. Slope factor is a convenient way of using the pitch of your roof to convert a 2D measurement to an accurate measurement of the roofs square footage.

Roof Slope |

## Calculate The Simple Roof Areas

On a simple hip or gable roof, multiplying the eave to ridge length by eave length will give the area to be multiplied by pitch factor. Ridge vent openings are best finished with coil rather than partial shingle. Using flat coil stock allows the ridge caps to lay flat and can also be formed with an extra water stop at the ridge opening.

Area for the roof in **Figure 3** is 1784 ft2 The blue dash line divides the roof into 2 rectangles. There is a small area calculated as 8/12 that is actually 4/12. On a small area such as this, it is better to err on the side of the higher pitch since it should not significantly affect the total.

**Pro Tip:** Pythagorean Theorem can be used to calculate the length of the valleys. A general rule of thumb is to add at least 12 lineal inches of valley material to be safe.

Figure 3. Calculating Simple Roof Areas

**Read Also: How To Extend A Metal Roof Overhang **

## How Do You Calculate The Square Footage Of Your Roof

Is it time for a roof replacement? Are you trying to figure out how much youll have to invest in your new roof?

If so, youre probably overwhelmed trying to learn everything that goes into the cost of your roof replacement. To help you understand the size of your roof investment, you first need to know the size of your roof. Thats why were going to break down how to measure your roofs square footage.

The team at Bill Ragan Roofing has been repairing and replacing roofs in Nashville and surrounding areas since 1990. We take extreme pride in everything we do, especially our workmanship.