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How To Measure A Roof For Shingles With Valleys

Builder Mike Guertin Explains 3 Ways To Calculate The Quantity Of Shingles You’ll Need For Your Next Roofing Job

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One of the biggest challenges for experienced builder and novices alike is accurately estimating materials for a construction projectespecially for roofs, because they can be difficult to access for taking measurements.

But dont fretIn this excerpt from my book Roofing with Asphalt Shingles, I describe three reliable methods for determining the area of a roof, plus Ive included tips for estimating the number of extra shingles youll need for waste, overlaps, and starter shingles.

Note: be sure to take your time and double-check your numbers when calculating the quantity of shingles, underlayment, flashings, and other materials needed for yourroofing project. The more accurate your estimates, the less time youll waste waiting for material deliveries during the project.

Tips For Getting Started

Tip 1: Measuring to the nearest inch along eaves and across gables can be done from the ground just dont forget the overhang.

Tip 2: If you know the dimensions of your previous asphalt roofing job, you can use this info to cheat a little. Typical 3 Tab asphalt shingles have tabs that are 1 foot wide with a vertical exposure of 5 inches. Make sure to physically verify these dimensions by measuring 4 or 5 courses. Counting the shingles can give you eave to ridge dimensions from the ground.

Tip 3: 100 Square Feet = 1 Square in Roofing Terms

A Handy Visual Guide To Dry Valleys That Wont Dam With

Around 65% of buildings with metal cladding will have signs of cut edge corrosion. Avoid using anything that will melt the galvalume coating such as a chop saw, torch or abrasive blade.

Common roofing errors jlc online roofing roof. A chalk line is then used to strike a line from the top of the valley to the bottom of the valley.

Easy gutter fixes you can diy how to install gutters. A nibbler is the most efficient and effective way to cut metal roofing panels.

Gallery treasure valley steel inc steel roofing. A nibbler works much like a jigsaw, only theres no table under the material youre cutting.

How to install a metal roof instead of shingles on your. A w or v shaped piece of metal, which is the valley component, is installed on top of the underlayments.

How to install a ridge with britmet lightweight metal. Around 65% of buildings with metal cladding will have signs of cut edge corrosion.

How to metal roof for cheap youtube metal roof over. Avoid using anything that will melt the galvalume coating such as a chop saw, torch or abrasive blade.

How to install aluminum soffits that are maintenancefree. Cut the panels from the ground instead of on the roof to.

How to install eave fascia metal roofing trim metal. Cut the shingles along the line created by this new row of ice and water shield, leaving the metal open to channel water.

How to shingle a roof laying asphalt shingles asphalt. Divide your verticle measurement by that number .

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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.

Installing The Roof Shingles

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You took the time to properly protect your roof against ice and water that tries to drip back underneath your shingles as it is flowing down, and now it is time to put the actual shingles on your home. Begin your shingle installation by laying a row of starter shingles along the lower edge of the roofline and nailing them down using roofing nails. With the starter shingles laid along the very edge of the roof, run a set of starter shingles along the sides of the roof as well, making sure that those rows come down and overlap the starter shingles you laid at the bottom.

Lay your first row of shingles so it overhangs the drip edge by about one inch. Put between four and six nails into each shingle below the tar line but above where the bottom of the next shingle will cross by about ½.

Do this on both sides of your roof and then install ridge cap shingles over top of the ridge. Start at the left side of the ridge and nail the first shingle on the right side. Lay the next cap shingle over the first so it covers that nail and nail it in the same way on the left side. Continue this all the way to the end of the roof. Seal the nail holding the final cap shingle with a bit of roofing tar to help prevent water from getting in.

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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.

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.

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Figuring Out The Square Footage Of Your Roof

While it may seem difficult at first, you can divide your roof into 10 x 10 roofing squares, a standard unit of measurement used by roofers.

But first, some terminology you’ll need to know:

  • Ridge – Where two sloped roof areas meet
  • Valley – Where two sloped roof areas meet , often with a metal channel running along the fold
  • Hip Roof – Type of roof where all sides slope downwards to the walls
  • Hip End – The triangle shaped end of a hip roof

Related: Roofing 101: What Are the Different Parts of the Roof Called?

Measuring A Roof Area

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For many people the idea would never cross their mind, that they may ever have the need to measure their roof for roof shingles.

Invariably for most homeowners, the time will come when somebody will have to measure their roof either when a replacement roof is needed, or when some structural change involving a permit, may become a requirement.

Due to the height and steepness of many roof configurations it is typically not advised that people attempt to measure their own roofs. But it can be very important to those who are purchasing a replacement roof, to understand how a roof should be measured properly, and why.

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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

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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

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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    Final: Double Check Your Work

    After you complete the installation you should keep a close eye on your home over the next few months. Look for signs of roof leakage in the roof, and look for any sections of the roof that seem to be flapping or blowing up more than they should be. A single mistake can leave a section of shingles ripping off and allow water right into your home. As long as you keep a close eye on your house you should be able to spot possible mistakes and problems before they become major issues on your home.

    Installing a shingle roof is a project that a homeowner can complete on his or her own, but it is not an easy project. It is something that you have to take the time to understand and evaluate before doing. If you are not confident in your abilities, it is much better to leave the task up to a professional instead of attempting the project and making a mistake. You should now have learned enough information to thoroughly know how to install roof shingles. However, feel free to get quotes from local roofing contractors above if you want to find out about roof installation costs in your area.

    Get started

    Hip And Ridge Capping

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    Now that you’ve got your field shingles secured all the way up the roof, you can finish off the peak with hip and ridge caps. Ridge cap shingles will straddle the peak of the roof to properly deflect water. You should begin on the side of the roof that is opposite to the direction of prevailing winds. These pieces overlap, much like the rest of the shingles, with the final piece nailed in place.

    You will need longer nails to secure ridge caps because the nails will also need to penetrate the field shingles below.

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    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 .

    What About The Waste Factor Should I Order Extra Roofing Materials

    You want to order extra material to account for waste. Waste factors vary.

    10%-15% is a good rule of thumb, but your results may be different. More complicated roofs will have a higher waste factor because there are usually more cut shingles around corners, walls, and edges.

    It is okay to have a few shingles left over. They can be saved in case there is roof damage later or if repairs need to be done in the future.

    So for the 24 square roof example, you would want to add 2.4 squares which equal about 7 or 8 more bundles.

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    Install Step And Dormer Flashing

    It’s 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 that’s closer to the peak, so the next step flashing in line will cover the nail. Don’t nail them down through the shingles. For information about flashing around chimneys, see Installing Chimney Flashing.

    Stick The Bottom Part Of The Underlayment To The Roof Of The House

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    Install the second course just like the first, using the guidelines on the underlayment to get the correct overlap. When an ice dam forms on a roof , ice and water can work their way up under the shingles and leak back into the house. Also, strong winds can blow rainwater under shingles. Self-stick roofing underlayment can prevent this because it sticks to the roof decking to seal out water. It also seals around nails, which keeps water from leaking through nail holes.

    Rolls of self-stick underlayment have a plastic backing so the material won’t stick to itself. The backing is separated down the middle. Line up the lower edge of the roll with the outside of the drip edge. Peel back part of the uppermost backing on the roll, and nail the top corner of the underlayment to the decking. Start pulling the roll across the decking using the backing, making sure the material is lying as flat and as straight as possible as you pull.

    You’ll be able to roll out long sections at a time if you have a low-pitched roof, but the underlayment may slip off the eaves on steeper roofs, so roll out no more than 10 ft. there . It’s important to make sure all your underlayment lies flat before you fasten it to the decking. Ripples and lumps can telegraph through the shingles and may be noticeable from the ground.

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