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Calculate Roof Area

Installing a new roof is a capital intensive affair that requires you to establish your budget in advance. Thankfully, it is easy to estimate the costs by calculating the roof area and then using the sum to determine the cost of shingles per square foot.

How to calculate the roof area

  1. Begin with calculating the area of your house in a plane parallel to the ground. If your house is rectangular, all you need to do is multiply the length and width of the building. If the shape of your house is more complex, simply enter the total area (after measuring the exterior dimensions) into the appropriate box.
  2. Determine the roof pitch of your house. Roof pitch is the slope created by the rafters. If you don’t know how to calculate it, head to our roof pitch calculator. You can input it either in degrees, as a percentage or as a ratio of x:12.
  3. Once you know these values, you will be able to calculate the roof area. Begin by converting the roof pitch to an angle expressed in degrees, using the following formulas:

pitch(%) = x / 12 * 100%

pitch(deg) = arctan [pitch(%)]

  1. Then, use the following equation to find the total area of the roof:

roof area = base area / cos[pitch(deg)]

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How to Estimate Roofing Materials

Although roofing projects are estimated and sold by the square, roofing material is often not sold in 1 square increments.

How Many Bundles of Shingles Will You Need

The average bundle of shingles covers 33.3 ft2, so three bundles of shingles are needed per square. Asphalt shingles range in price from about $25 per bundle for a standard 3-tab style to around $50-$75 or more for an upgraded architectural style.

Since transportation is a major cost factor, expect prices to vary by location. A typical bundle of shingles weighs about 75 pounds, while some premium products can weigh over 100 pounds per bundle, so consider delivery of materials.

How Many Rolls of Felt Will You Need

Roofing felt is sold by the roll. The average roll of 15-pound roofing felt covers about 400 ft2, or 4 squares, while the average roll of 30-pound roofing felt covers about 200 ft2, or 2 squares.

Rolls of felt are 36″ wide x 144′ long for 15# and 72′ long for 30#. Consider other underlayment options as needed, such as rubber or tar products.

How Many Nails Will You Need

Nails will also be required for any roofing project. The average 3-tab shingle needs four nails per shingle. High wind areas and other types of shingles may need more. 320 nails will be needed to install a square of standard 3-tab shingles, assuming four nails per shingle and 80 shingles per square.

Remember, be wary of too-good-to-be-true estimates that promise cheap and fast results. Investing in name brand materials and quality service will save you time and money in the long run.

How to measure your roof area from the ground

A more accurate way to calculate the area of the roof than using Google Earth is to get outside to estimate the roof pitch and the base area of the property. Using these two figures, we can get a good idea of the shingle roof’s square footage and estimate your asphalt shingles’ needs and costs. This DIY technique can be helpful, especially if you are not comfortable getting on your roof, or if you have limited access to it.

Ground measures only work well for a gabled roof, since there are usually just two main rectangular pitches to calculate area for. For more complex roof shapes, like hip roofs, you’ll need to work with a roofer or measure from on top of the roof itself to calculate its total area.

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How To Figure a Pitch On a Roof ?

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.

What is a 4/12 roof pitch?

A 4/12 is a roof slope that rises by 4 inches for every 12 inches across. This forms an angle of 18.5° between the horizontal section and the roof, and creates a gentle incline that is seen as a midpoint between a low-pitch and medium-pitch roof. A 4/12 slope is enough to accommodate water runoff, but is not suitable for regions that are affected by heavy snowfall. Standard asphalt and composition shingles are the best for a 4/12 roof; rubber and wood shingles are unsuitable.

What roof pitch is 60 degrees?

Roof Angle in Degrees to Rise-in-Run
 
Convert Roof Slope from Degrees to Rise-in-Run
59°19.971 in 12
60°20.785 in 12
61°21.649 in 12
62°22.569 in 12
Conventional slope roofs, with a pitch between 4/12 and 9/12, are the most common in residential work. Roofs with a pitch exceeding 9/12 (37 degrees) are termed steep slope roofs. In commercial work, low-slope roofs (with a pitch between 2/12 and 4/12) are most common.
 

Is a higher pitch roof better?

Fewer snow worries: Even without a cold roof system, a steep roof is generally better in a snowy environment (which is why you see those dramatic A-frame homes in colder areas). … Ice melts more easily on a steep slope, preventing the build-up of ice patches or dams that can force moisture down into your roof.
 

What pitch roof can you walk on?

The roof’s pitch is the angle of the roof, usually presented as the inches of vertical “rise” over 12 inches of horizontal “run.” Generally anything above a 7/12 is considered a non-walkable roof and requires some extra equipment and usually some extra cost to the customer.
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What is the best roof pitch for snow?

Roofs in snowy climates should have a slope of at least a 10-degree pitch minimum. A steeper angled roof sheds the snow more quickly. While the angle of the roof helps shed snow, adding too many angles to the roof for a more aesthetic effect could cause structural problems with snow shedding in the wintertime
 

What is the minimum roof pitch for metal roof?

The minimum slope for lapped, non-soldered seam metal roofs without applied lap sealant shall be three units vertical in 12 units horizontal (25-percent slope). The minimum slope for lapped, non-soldered seam metal roofs with applied lap sealant shall be one-half unit vertical in 12 units horizontal (4-percent slope)
 

How do roofers walk on steep roofs?

As you advance toward the top of the roof, take it one slow step a time. Many experienced roofing experts recommend walking sideways, placing both feet together with each step. When it comes time to dismount, remain crouched down just slightly as you descend.
rooftop measurements

How To Figure Roof Pitch

There are two suggested ways to measure a roof pitch.

The first is from the top of the roof. Simply mark a level at 12″. Keeping the level balanced measure the distance from the level to the roof surface. If a roof has many layers of shingles your measurement could be slightly inaccurate using this method

The second is to measure from the bottom of the rafters. Measuring the pitch is still the process but you you can measure the roof pitch from three different locations using this preferred method. The underside of a rafter on an overhang at the bottom of the roof, the underside of a barge rafter on the gable end, and the underside of the rafter in the attic.

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If you’re having a roof installed, keep in mind that costs go up as the roof pitch becomes steeper. This is because contractors will need specialized equipment to put steep-pitched roofs into place, and this task can mean additional safety risks for the workers, so that will have to factored into the expenses.

There’s good news, though; having a steeper pitch means that water and ice flows off the roof better instead of sitting on the roof and potentially causing damage over time. A steep pitch can then actually be considered a good home improvement investment.

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Method Three: 

If you know the total height of the peak and the width of the roof you can also find the pitch with a little math. For example, if the peak is 4 feet and the total roof with is 20 feet, the total rise is 4 feet, or 48 inches.

The total run is the distance from the peak to the edge of the roof, which in this case is the total width divided in half, which is equal to 10 feet or 120 inches. Since pitch is the rise over a 12 inch run, divide the run by 12 to get the multiplier, in this case 120 ÷ 12 = 10.

Now, divide the rise by the multiplier to get the pitch, e.g. 48 ÷ 10 = 4.8. The pitch of this roof is 4.8:12. The calculator above can handle much of this math.

Roof Pitch Calculator Results Explained

Slope – The slope of a roof is represented as X/12, where X is the number of inches in rise for every 12 inches of run.  This is very useful information for many purposes, especially for roof framing – the slope, sometimes called pitch, is calibrated on speed squares.

Angle – The angle of a roof is the same as the roof’s slope, except instead of being represented as X/12, it is represented in degrees.  This is useful because sometime you may need to cut a bevel with your circular saw that is not calibrated using roof pitch style – this setting on circular saws is calibrated in degrees.

Rafter Length – The rafter length results, from this calculator, represents the length of line L on the diagram(s).  Note that this is not the actual length of the rafter.  It is the length of this portion of the rafter.  If you plan to have overhang, etc. the rafter member will be longer.

Pitch – Is the incline of the roof represented as the ratio of rise to the span (twice the run).  For example, if the roof rises 4 feet and the span is 16 feet (twice the run), then the pitch is 4/16, or 1/4.

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How To Calculate Pitch Of Roof

Roof Pitch is a term describing how steep or flat your roof slope is.  The combination of two numbers are used to display or show the roof pitch.  Two most common methods (4/12 or 4:12) are used for marking the pitch of a roof.  On blue prints architects & engineers usually display the pitch of a roof in the format shown on the image where number (4) represents a rise and number (12) represents a length.  This means if a roof rises 4′ in the length of 12′, your Roof Pitch would be 4/12 or 18.43 degrees.

Calculating Peach of Roof

  1. Measure 12 inches from one end of the level and make a pencil mark on the level at that point.

  2. Place the end of the level against the bottom of a roof rafter and hold the level horizontally so that it’s perfectly horizontal.

  3. Measure straight up vertically from the pencil mark on the level to the bottom of the rafter. The resulting measurement is the roof’s rise. Its pitch is the rise measurement over a 12-inch run.

Low Pitched Roofs

A low pitched roof is anything that is any roof with a pitch of 3:12 or less. Many roofing shingles do not allow applications onto roofs at this pitch. More commonly, roll on membranes such that use heat to bond seams together is used as a roofing material.

Pros

  • Uses the least amount of roofing material
  • Easy to access and install

Cons

  • Cannot handle heavy loads
  • Shingles often not rated for shallow roofs
  • Medium-slope – 4:12 to 9:12, which are often mathematically reduced and expressed as 1:3 and 3:4. Roofs with pitches of 6:12 are the most common. A nice balance between water and snow run-off and ease of access.
  • Steep-slope – Any pitch above 9:12. These roofs may require extra fasteners, and these steeper roofs are very challenging to walk on.

How much pitch should a gutter have?

Once you’ve re-pitched your roof, the next thing to concern yourself with is the gutters. Efficient gutters have a pitch that allows rainwater to drain away from the roof and home. This is essential for preventing floods and leaks, avoiding the harm of nearby landscapes, and protecting your home’s foundation. Don’t take gutters lightly.

Most roofers will set the slope at 1 quarter inch per 10 feet of guttering. So, if you have 30 feet of guttering, your downspout should be 0.75 inches lower than the other end (0.25 x 3 = 0.75). Simple enough, right?

Roof pitches matter

Not many homeowners think about their roof pitch often (heck, not many people even know it exists), but understanding and maximizing your roof’s pitch increases your home’s longevity and lowers the amount of time you’ll have to see a roofer. Reread this article and take the time to learn more about roof pitches.