Expressing Roof Slope In Degrees
The rest of the English-speaking world uses degrees, which seems simpler, but it takes a few extra steps to figure it out mathematically.
It also doesnt immediately convey as much information about the roof on a practical level as the rise-in-run ratio expression.
To express the slope in degrees, you divide the rise by the run and find the inverse tangent of the result.
But you still need to know the rise and the run, the X-in-12, in order to find the roof slope in degrees, unless youre using a slope finder that tells you the slope in degrees.
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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
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.
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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.
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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.
Notes On Calculating The Area Of A Roof
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The Operating Cost Of Your Roofing Contractor
Every roofing contractor has operating expenses to keep their business going. These operating costs will always factor into the price of any roof work that needs to be done.
Some common operating costs are:
- Building cost and utilities, shop and truck yard
- Advertising and promotions
- Payroll and payroll taxes
- Taxes
These are just some of the fixed operating costs that it takes to run a business. No matter if a roofing company does a simple repair or replaces 10 roofs, these are the costs that have to be paid every day. No matter what work you get done or what service you need, operating expenses will always factor into an estimate or final cost.
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.
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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 roofs 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, youll need to work with a roofer or measure from on top of the roof itself to calculate its total area.
Make The Calculations For Your Roof Pitch
A roofs pitch is its slope. Lower pitch generally means an easier install, which means a lower price. Low pitches rise three inches every foot of roof length, while medium pitches rise 6 inches every foot and high pitches rise a foot for every foot of roofing.
In order to properly calculate the total pitch of your roof, youre going to need a ladder, a tape measure and a level. What youre going to want to do is measure up the roofline by one foot. Make sure to set the edge of your level at that spot . With the level in place, tip it so that its completely level from the spot you measured to out over the edge of the roof. From the end of the level, measure downwards to the bottom edge (so that your measurement goes to the bottom of the roof.
Whatever the total vertical distance is, is the overall pitch of your roof.
So to recap: the level should be one foot in total length or more. Use your measure to measure up your roof from the base up 12 inches.
Place the level at the 12 inch mark, outwards at a ninety degree angle. Measure downwards from the level to the roof baseline and youll have the pitch. 3 Inches is considered a low pitch, about 6 inches a medium pitch and 12 inches a high pitch.
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Find The Area Of The Roofs Footprint
Determine the area of the roofs footprint, which is the area covered by a roof regardless of slope .
Google Earth Pro makes finding the area of a roofs footprint pretty easy with the measuring tools they have available, but you can also simply measure the dimensions of the building on the ground and figure out the area that way .
Dont forget to take into account overhanging eaves or any other areas where the roof extends beyond the exterior walls of the building.
You will also need to increase your total footprint area to include any areas where one roof section overhangs another roof section. Youll probably be trying to estimate the entire area of a roof.
Figuring out the area of a roofs footprint is easier if you print a satellite image of your roof to write your measurements on. The white thing on the left is a carport with a metal panel roof, and the dark rectangle at the bottom left is a covered porch that was apparently added after the house was built.
Understanding The Roofing Calculator Inputs
House Base Area – This is the surface area of the house, the parallel plan with the ground. You can simply calculate the base area of your house if it has a rectangular shape. However, for more complex shapes, you would either have to calculate each part of the shape individually or know what the area is priorly. If your house has a complex shape, the calculator would give more accurate results if you separate it into parts and calculate each part on its own.
Roof Pitch – The roof pitch is measured as a ratio of the vertical rise of the house over its horizontal run. In the U.S., this ratio is shown as the number of inches of vertical house for every 12 inches of horizontal run. For example, if the roof pitch is 5/12, this means that the roof rises 5 inches for every 12 horizontal inches.
Price – The calculator allows you to input the estimatedprice per square footof constructing the roof in order to find out how much would be needed in total to cover the whole roofs surface area.
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Finding The Size Of The Roof In Squares
Roofing contractors estimate projects and materials by the square, so it is crucial to find this measurement to estimate the amount of material needed accurately. A square simply refers to a 10 x 10 square of roofing. This is simply 100 square feet of roof.
To find the squares, divide the overall roof area by 100 and then round up. For instance, if the roof is 1550 square feet, then it is 16 squares.
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.
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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.
Roofing Square How Contractors Measure And Price Roofs
Roofing square is the most common measurement unit used by roofers, as well as contractors from many other trades. It greatly simplifies communication between architects, contractors, roofing manufacturers, suppliers and even clients. Its much easier to say 25 squares than 2507 square feet, and there is less information lost in translation.
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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.
Roofing Squares: A Way To Measure Your Roof
So youve decided to re-shingle your roof, youve called the contractor and all seems well until the contractor comes down and you hear a term youre not familiar with, roofing square
What? you ask yourself, wondering what exactly the person you hired just said to you, did they mean a square foot, a panel, something else entirely? Dont worry, youre not alone. Its a question we at Rennison Roofing get all the time!
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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 A Roof
Getting accurate roof measurements can be difficult but with this roofing calculator, youll be well prepared to take measurements of any roof. Whether youre a contractor looking to train a new employee or a homeowner looking to do some renovations, youll find this guide helpful for any roofing project. Use the step-by-step guide below to accurately measure your roof and estimate roofing costs.
Step 1: How to Calculate Your Roof Square Footage
First, measure the length and width of each surface on the roof, then multiply these values to get the square footage of that surface. Make sure to document the number of chimneys, skylights or other obstructions and include dormers in your measurements. Youll also be recording the length of your house throughout this first step in order to calculate your total area.
Add up the square footage for each surface to get the total square footage of your roof. For example:
Step 2: How to Determine Your Roof Pitch
The next step is to measure the pitch of the roof deck. Youll need to figure out the vertical distance over a 12 horizontal segment . Record these values as roof rise over run, with the vertical measurement listed first and the horizontal second.
Its important to keep in mind that the roof pitch will be dramatically different for homes with a flat roof than homes with a steep roof.
Step 3: Calculating Roof Squares
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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
