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:
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.
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.
Install Step And Dormer Flashing
Its possible to reuse existing step flashing and dormer flashing, but the best way to get a watertight seal is to tear off the siding in those areas and install new flashing. Start by running self-stick underlayment at least 6 in. up onto the walls. This provides an additional barrier if water does get past the flashing. Cover the front wall first and then work your way up the side wall. Overlap the sidewall underlayment around the corner onto the front wall about 1 in. or so.
Install the shingles right up to the front wall. Cut a couple of inches off the vertical portion of the dormer flashing, and run the horizontal portion past the side wall that same distance. Nail the dormer flashing to both the wall and the shingles.
Make a 1- to 2-in. cut with a tin snips at the bend in the first step flashing. Run a bead of sealant on the corner edge of the dormer flashing, and then run that step flashing past the dormer flashing the same distance you made your cut. Bend the step flashing around the corner onto the dormer flashing with your hammer.
Install your next row of shingles over that first step flashing, then cover that row with a step flashing, and so on. Nail the step flashing to the wall toward the top of the flashing at the end thats closer to the peak, so the next step flashing in line will cover the nail. Dont nail them down through the shingles. For information about flashing around chimneys, see Installing Chimney Flashing.
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Measuring The Length And Width Of Each Plane By Hand
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.
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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.
How To Estimate The Size Of A Roof
If youre replacing a roof, the first consideration needs to be the roofs size so you can accurately estimate project materials.
In the U.S., roofs are measured in square footage, and roofing contractors typically quote projects based on the size of the roof in squares. Consequently, gathering the size of the roof in squares and square footage is the first step.
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How To Measure Your Roof From The Top Of The Structure
The most accurate way to measure your roof is by being on top of the roof itself. You can make sure each roof sections slope area is accounted for. Youll need some graph paper, measuring tape, and a calculator. For our example, well use a hip roof, though you can use this technique to measure any shape roof with varying complexity.
How Many Bundles Of Shingles Do I Need
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.
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References and Further Readings :
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How To Measure Your Roof With Google Earth
Using your computer to get a ballpark estimate of your roof area is easy and fast. However, using satellite imagery may not be an ideal solution if your structure is in a very remote location that hasnt been 3D scanned. Thats because well need to grab an accurate representation of your roofs pitch for measuring purposes. From above with a 2D image, everything looks flat. If you were to just measure your roof area from directly above, you wouldnt be accounting for its pitch, or slope.
Consider two homes with the same base area square footage, but one of them has a much steeper roof pitch than the other. That structure would need to be taller, and there would be a lot more roofing material to account for. If youre just measuring from above in 2D, both of these structures might look identical. If you dont account for roof pitch, youre going to underestimate your materials requirements, which could be a costly mistake.
Satellite technology has progressed a lot in the past few years. With , you can easily find your address and a 3D replica of your structure, including your roofs pitch. Lets get to it. Once you load the site, youll be presented with our beautiful planet:
While you can switch to 2D mode by clicking the button in the lower right, youll want to stay in this 3D view so you can get a good view of your roofs pitch.
Which Should I Use To Re
Asphalt, wood or slate are the preferred material for steep rooftops. However, when re-shingling a hip/steep one, consider the type of shingles that were used previously. Using a material of comparable weight and quality can help ensure that the structure is designed to support the new weight. If heavier ones must be used, then the home may need to be reinforced before the project can proceed.
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Whats Your Roof Slope
You will also need to know the slope of your deck.
To determine this, measure the vertical rise of your deck in inches over a 12 horizontal distance.
If this rise is 4, then your roof slope is 4 in 12.
Roof slopes are always expressed with the vertical rise mentioned first and the horizontal run mentioned second.
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How Do You Calculate The Square Footage Of 1212 Shed Roof
Figure out the area of the shed plus the overhangs: determine the squre footage of the shed foot print by measuring the length and width of the shed including the overhangs. Assume the overhangs are 1 feet both sides eves and rake then you have 2 feet extra, so each dimension for 12×12 shed roof with overhangs is around 14×14 = 196 square footage.
Find the roof pitch or slope:- the roof pitch is the amount of slope. The slope is described by the rise in inches or how far up it goes over the run in inches or how far horizontal it goes. We will use a 6 in 12 pitch. For every 6 inches the roof goes up to the peak it goes 12 inches horizontally.
Calculate the square of rise and run and sum it:- square of rise 6×6=36, square of run = 12×12 = 144, add both 36 +144 = 180.
Find the square root of the sum:- square root of 180 = 13.417
Sum divide by 12 to get the product:- square root of 180 = 13.417 is divided by 12 as 13.417 ÷ 12 = 1.118, hence 1.118 equals the product
Multiply the product by the flat roof area and divide by 100:- our 12×12 shed square footage with overhangs is 196 sq ft, so 1.118 x 196 = 220 square feet, 220 / 100 = 2.2 squares.
Add 10% for wastes:- wastages 10% of 2.2 squares = 0.22, so final squares of shingles do you need = 2.2+ 0.22 = 2.42 squares, it is rounded to 3 squares.
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Can You Install A New Roof On Top Of Old Shingles
Many homeowners wonder whether or not its a good idea to install a roof on top of existing shingles .
The biggest reason for keeping the existing layer of old roofing is obvious extra cost. As we just explained above many people would rather avoid spending an additional $1,000 on removing the old shingles.
Despite the high cost, doing this is absolutely essential! Leaving the old material will greatly accelerate the disintegration of the new roof and shorten its life cycle.
This is because ventilation is reduced, which in turn increases the average temperature of the shingles, causing the product to dry up quicker and the granules to start falling off faster.
Another reason why you should NOT leave the old shingles is because a roofer will typically not install underlayment between old and new roofing. If there are pre-existing problems in the leak prone areas: such as skylights, chimneys, vents and valleys, installing new shingles will not solve them! This means that your new roof will continue to leak.
Failing to tear off old roofing will also negatively impact your warranty. Most large shingle manufacturers explicitly state that your material and labor warranty automatically becomes void, if their product was installed on top of an old roof.
In most states, the building codes require that you remove the old roofing materials, if there are more than two layers of it already there.
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S To Measuring Roof Square Footage
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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.
Determining Roof Area For Shingles
You may occasionally need to purchase roof shingles for a repair project or to re-roof your home. Roof shingles come in various styles and shapes, but the basic calculations to determine roof area are the same.
Shingles and Roofing Materials
Shingles come in bundles of 3 which equal a square. Each square represents 100 square feet of roof area. When making calculations to determine how many shingles to purchase, keep in mind that you will not only need enough for the correct square footage, but you will also need 10 to 15 percent more shingles to accommodate dips and valleys in your roof or for extra coverage.
Additionally, you will need to purchase:
- Roof ridge shingles
Asphalt paper and flashing are sold in rolls. You will need enough asphalt paper to place under all of the shingles for your entire roof area. Flashing usually comes in 16-inch wide rolls or 6×6 or 8×8 square inch steps. Step flashing is used around chimneys, doorways and at the points where side walls come together.
Hip and ridge vent requirements vary according to local building codes. Be sure to purchase all of your roofing materials in advance of starting the project. Also, keep in mind that roofing materials are run in batches that have variations in quality and color. If roof shingle bundles are purchased in differing lots, it may result in inconsistencies that lead to leaks and other defects in the roof.
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Finding The Total Roof Area
Once the area of the roofs footprint is known, the overall roof area can be found by accounting for the roofs pitch. The pitch of the roof is the rise over a 12-inch run. Use our roof pitch calculator to find the pitch of your roof.
Next, multiply the footprint of the roof by the multiplier below for your roof pitch to find the overall roof area.For example, a 4/12 pitch roof that is 100 square feet:
100 × 1.054 = 105.4ft2
Roof Pitch Area Multipliers
How To Measure A Roof For Shingles From The Ground
Remember when your high school algebra teacher said you needed to know how to calculate slope. He may have been thinking about measuring the square footage of a roof.
This method allows you to calculate roof slope and determine the roof area while keeping both feet firmly on the ground.
Begin by measuring the distance from the edge of the eave to the point at which you can barely see the slope of the roof. This works best if you can attach the tape measure to the eve, then walk to the appropriate place and take the measurement at eye level.
This measurement is the horizontal run of the roof. Now, stand under the gutter of the roof you are measuring the slope for and measure the distance from your eye to the roof overhang. This is the roof rise.
Divide the roof rise by the horizontal run to get your roof pitch. For example, if the rise is 60 inches and the run is 120 inches, youll have a roof pitch of 6/12.
As in the method described above, measure the length of the roof from the edge of one eave to the other and the width from one eave to the other. For example, a roof that measures 60 feet by 40 feet would be 2,400 square feet.
Next, use the table below to determine the slope factor. In our example, the 6/12 roof would have a slope factor of 1.118. In our above example, you would multiply 2,400 square feet times the slope factor to get the total square footage of 2,683 square feet.
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