How To Figure Roof Size

How Many Roofing Shingles Do I Need

To estimate how much roofing material you need, such as bundles of architectural shingles or rolls of synthetic roofing underlayment, you need to know the total square footage of your roofs surface.

How to Calculate Total Square Footage of Your Roof

To find your roofs total square footage:

Example #1: Shed Roof with One Roof Plane

For example, this shed roof has one roof plane.

Multiply length times width :

A x B = 40 x 30 = 1200 sq. ft. for the total square footage of the roof.

Example #2: Gable Roof with Two Roof Planes

This gable roof has two planes.

So to derive the total square footage of the roof, you would:

For example:

• Plane 1 : 40 x 30 = 1200 sq. ft.
• Plane 2 : 40 x 30 = 1200 sq. ft.
• Plane 1 + Plane 2 = 2400 sq. ft. for the total square footage of the roof.

How Do I Show Dimensions On Google Maps

Measure distance between points

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Calculate The Complex Roof Areas

Most roofs in Canada would be considered on the complex side. Multiple adjacent pitches, dormers, and turrets are common. Keep in mind that an experienced metal roofing contractor will need to factor in extended labour time for areas of your roof that will require precision metalworking skills.

Start by finding the footprint area and multiply by the correct slope factor determined by pitch . In Figure 4 below, the dashed blue lines give a simplified view of the footprint. Multiply L x W to calculate the area for each rectangular section. Note the area of 77ft2 that needs to be subtracted for the recessed area.

Once the footprint including overhang areas have been determined for each area, find the appropriate slope or pitch factor in the chart below. For example, a roof area with an 8/12 pitch has a slope factor of 1.202 so 2053ft2 x 1.202 = 2468ft2 total roof area.

A Note about complex roofs: Complex roofs need more accessories and trims thaneasy roofs resulting in a slightly higher total cost/square foot.

Figure 4. Calculating Complex Roof Area

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Download And Install Google Earth

The first thing you need to do before you can measure a roof with Google Earthis download and install .

Google Earth Pro used to be the paid version of Google Earth , but its free now.

It includes tools that werent available on basic Google Earth, the most relevant tool in this case being a measuring tool that allows you to measure the area of a polygon.

You can download it at:

What You Will Need To Measure A Roof:

To measure a roof you will need the following tools:

• Tape measure preferably 100 feet long you can get one at Home Depot or Lowes for about $17 + tax, and if you dont remove the wrapping, you can later return it, since you will rarely need it again .
• 2 feet level will cost you about $15 at Home Depot or Lowes, etc. You will need the level to get the exact roof pitch. You can also estimate your roof pitch or calculate it using simple math and geometry, and without the level.
• A 16 or 24 tape measure $5 to $10.
• A pencil and a notepad to write down your measurements.
• You may also need a ladder a 20 extension ladder will cost you about $100, and will come useful for most homeowners for example if you need to clean your gutters. Always get a ladder stabilizer bar it only costs $20, but will make it a lot more comfortable and safer, as it prevents the ladder from sliding left and right, and you will not damage your gutters.

Lets assume we are measuring a simple ranch-type house as these are very common and easy to measure. If you have a different type house or roof, you can still use this roof measuring guide, with some adjustments.

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What Is A Roofing Square A Comprehensive Guide

By: Author Ryan M.

A roofing square is the most common unit of measurement for materials that are used to cover roofs. Theres a tool used for convenience but theres also a quick way to determine the answer:

What is a roofing square? A roofing square, often known as a square of roofing shingles, is the quantity of material required to cover 100 square feet of roof area. Contractors, manufacturers, and suppliers use the phrase as a shorthand to define the size of a roof. A 2,000 square foot roof, for example, is 20 square.

How Do You Calculate The Slope Of A Roof

When referring to roofs, the term pitch means two things. Most of the time, people use this term to refer to the roofs steepness. But for carpenters and handymen, they believe that the terms more accurate meaning is the overall dimensions of the roof. Either way, lets see how you can calculate the slope of a roof without using a roof slope calculator:

1. Measuring the slope from the rafters

• The most precise way to find the roofs slope is by measuring it from the underside. Access one of the rafters then take the measurement this way.
• Use a level against the underside of the rafter youre measuring to get the most accurate value.
• Locate the levels 12-inch mark. If it doesnt have this mark, use a tape measure to locate the mark and draw a mark on it.
• Take the measurement of the vertical distance from the rafter to the level.
• Write the slope down using the measurements youve taken.

2. Measuring the slope from the surface of the roof

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How To Measure A Roof

This article was co-authored by David Bitan. David Bitan is a roofing professional, licensed contractor, and the owner and founder of Bumble Roofing based in Southern California. With over 12 years of construction industry experience, David specializes in restoring, repairing, and maintaining residential, commercial, and industrial roofs. With over 60 years of combined experience, Bumble Roofing provides easy, friendly services to structures including residential, commercial, industrial, multi-family, and government buildings along with hospitals, hotels, and churches.There are 13 references cited in this article, which can be found at the bottom of the page. This article has been viewed 357,244 times.

Measuring your roof is the first step in a successful re-roofing project. You can actually get an estimate of your roof’s measurements from the ground if you’d rather not climb a ladder and get up on the roof yourself. Otherwise, you can climb up onto your roof to take more accurate measurements. Either way, we’ve got you covered! This article will walk you through each process step-by-step.

How To Determine Roof Pitch

Heres how to measure and calculate roof pitch from inside your attic.

• Flipboard

The angle, or pitch, of a roof is calculated by the number of inches it rises vertically for every 12 inches it extends horizontally. For example, a roof that rises 6 inches for every 12 inches of horizontal run has a 6-in-12 pitch.

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Can You Shingle A 3/12 Pitch Roof

You can shingle a 3/12 pitch roof, but special application measures should be taken to prevent leakages at some point down the line. Some kind of protective, waterproof membrane should be put down underneath the shingles, as well as using shingles that are recommended by the manufacturer for that slope. You can find this information on the shingle packaging. This issue with these low sloped roofs comes from the flow of water not being quick enough to prevent water from flowing under the shingle and into your ceiling.

Calculate The Square Footage Of The Roof Area With The Roof Pitch And Base Area

Find your roof pitch from the first step in the following table and multiply the amount you just got by the corresponding roof pitch multiplier. The result is the total roof square footage youll need to get roofing material for.

In our example, the roof pitch was 6/12. The pitch multiplier would be 1.118. So, take the 2,100 square feet, multiplied by 1.118 to get 2,347 square feet of roofing material. Since roofing material like shingles come in squares of 100 square feet apiece, wed need at least 24 of them. If you have a relatively flat roof , you can simply avoid using a pitch multiplier and make sure to round up on your equipment estimate.

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Calculate The Surface Area Of The Roof

Take the area of a roofs footprint, say its 5,000 square feet, and multiply 5,000 by 1.118.

That gives you 5,590 square feet, which is the actual area of the surface of the roof. And thats what you were looking for.

This applies to rafter lengths as well as areas. A rafter for a roof with a 6:12 slope will be 1.118 times as long as the horizontal length that it covers.

What Roof Pitch Is 30 Degrees

A 30° roof pitch is roughly the same as a 7/12 roof pitch. To convert from degrees to the American ratio:

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Cost To Install Plywood Sheathing Or Replace Roof Decking

The average cost to replace roof decking in a 2,400 square foot home is between $1,050 and $1,575. It will take approximately 75 sheets of plywood sheathing at an average cost of $14 to $21 per sheet. A smaller 1,100 square foot home will only need around 34 sheets for an average price of $600. For roof sheathing, plywood typically comes in sheets of 4 by 8 that measure either 11/32 or 3/8 thick.

Cost to Replace Roof Decking

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What Is A Roof Pitch Multiplier

A roof pitch multiplier, also known as a roof pitch factor, is a number that, when multiplied by the area covered by a sloped roof, gives the actual area of the roof. The math behind this number is that it is the square root of 2 + 1). Roof pitch multipliers are extremely useful in estimating the amount of material required to fit your new sloped roof, as conventional mathematics will leave you short!

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Sizing Roof Rafters Example 2

Now lets try another example, but this time a span will be given and you must select the correct size lumber to be used given the following scenario:

Question: When the ceiling is not attached to the rafters and where Hem-fir #3 roof rafters are to be spaced 12 inches on center supporting a snow load of 30 psf and a dead load of 20 psf, what is the minimum allowable rafter size when required to span 14-0 in length?

First step, lets collect all the given information within the question:

• Ceiling not attached to rafters and a snow load of 30 psf: Use Table R802.4.1
• Roof Rafter Spacing: 12 inches
• Species and Grade: Hem-fir #3
• Roof Rafter Span: 14-0

Now lets find the minimum allowable rafter size given the above scenario:

Therefore given the above example, the minimum allowable rafter size for Hem-fir #3 lumber spanning 14-0 is a 2×10 since it can span 14-5. A 2×8 member for example cannot be used since it can only span 11-9.

To Learn more about the design and construction of wood roof framing, be sure to check out Section R802 of the 2018 International Residential Code .

Fun Tip: To learn how to easily size ceiling joists, be sure to check out this POST.

Hopefully given the above examples you can find it easier to size wood roof rafters per the Tables within the International Residential Code.

In conclusion, lets take a quick second to answer some common frequently asked questions related to roof rafters.

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Calculate Your Own Roof Truss

Our roof truss calculator will help you know the exact measurements for building or fixing your roof.

All you need to do is add the numbers in. The calculator will generate a printable professional drawing you can use while you work.

A details explanation of how to use the calculator is down below. Please scroll down.

inches

inches

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What Is A Bundle Of Shingles

A package of roofing shingles is called a bundle.

How many bundles of shingles per square?

Laminate or architectural shingles, one of the most common types of roofing shingles, are generally packaged in three bundles per square:

3 bundles = 1 roofing square

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

Here are a couple more examples:

How Do You Calculate A Roof Pitch

Roof pitch refers to the slope which the rafter creates. You can assess this in two ways, either as the roof pitch angles which the rafters make with the horizontal or the proportion between the run and the rise of the roof. Often, you express roof pitch as the ratio between the rise and the run in the form of x:12.

You can divide roofs into these categories:

• Flat roofs which arent perfectly flat require a small slope to allow for water runoff. Generally, such roofs have a pitch ranging from 1/2:12 to 2:12.
• Low-pitched roofs are generally difficult to maintain and you need special materials to prevent leaks. These roofs have a pitch less than 4:12.
• Conventional roofs are the easiest to construct and you can walk on them safely. They have a pitch ranging from 4:12 to 9:12. High-pitched roofs often need extra fasteners and their pitch can be as high as 21:12.

You can also calculate roof pitch even without using a roof slope calculator. Use the following formula which also describes a right triangle. Here are the equations you may use to solve for the length of the slope and the rafter:

rafter² = rise² + run² rise / run = pitch, pitch = tan ,

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Roof Slope Multiplier Chart

Since the roof slope multiplier is so important to estimating the area of a roof, weve put together a quick reference chart.

We also have a much more complete roof slope multiplier chart that includes slopes by the half inch and slopes up to 30.5-in-12.

If youre using the table below to help you figure out the area of a roof, you should consider getting yourself a construction calculator. That way you can instantly calculate the factor for any slope, among many other useful things. This one is very good.

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.

To learn what affects the cost of your replacement, check out 9 Factors That Impact the Cost of Your New Roof.

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Roof Rafter Span Tables

As mentioned above, the span tables within the code list the allowable roof rafter spans for common lumber sizes based on what design load scenario is applied.

According to Section R802.4.1, roof rafters are to be sized based on Tables R802.4.1 through R802.4.1. It is very important to select the correct table.

Now in order to select the correct table, we must understand 2 things: Which Live Load is to be use and whether or not the ceiling joists are attached to the roof rafters.

We touched on the loads earlier but let us go over why it is important to know if the ceiling joists are attached to the roof rafters or not.

According to Section R802.5.2 each roof rafter must be tied across the structure via ceiling joists or rafter ties. When the ceiling joists are attached, they act as the tie. When they run in the opposite direction creating a scenario where they are not attached to the rafters, then rafter ties can be used to achieve the tie requirement.

This connection is important because it resists the horizontal thrust from gravity loads and rafter thrust caused by the uplift from wind loads.

Using either a rafter tie or the ceiling joists themselves can vary slightly in the size of the roof rafter used which is why the code creates two types of span tables. One for when ceiling joists are used as the ties and one when they are not used, thus requiring the rafter ties.

Now lets go over what information is found on the tables.