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How to Easily Measure and Estimate Your Roof

Yes, becoming a professional roofing estimator / salesman could easily earn you well over $60,000.00 per year, with the right company. But, the main point of this DIY guide is to show you why it is important that a man who measures your roof and gives you an estimate knows how to do it correctly. This guide will also show you a few basic ways to estimate your roof from the ground by teaching you easy techniques to figure roofing squares, and estimate relative roof difficulty, which is the major factor in roof estimating.

Why learn How to Estimate Your Roof?

Let's face it, making even a relatively small mistake when performing a roofing estimate could put a huge financial hole in your wallet! For instance, being off by just a few roofing squares in the already expensive metal roofing job could cost you thousands. What is even more shocking is that there are many so called professionals in the field, who frequently make mistakes that cost consumers a lot of money. Consider this as one of the many countless examples of roof measuring mistakes made by the roof consultants giving estimates for a new roof to unsuspecting homeowners. Recently, we were providing a roofing estimate for a homeowner who was interested in installing a metal roof on his ranch house. During our conversation we were shocked to find out that a salesman from a competing company was off by as many as seven roofing squares, when he provided a roofing estimate for this homeowner.

Roof measuring mistakes may cost you thousands

It is an undeniable truth that a Roofing project can be a great expense for the home owner. Now, in metal roofing, which typically costs three to four times what the regular roof may cost, a small mistake in estimating roof size can cost us 3 times more than a similar mistake in an estimate for a regular roof. No matter what type of roof you are considering, a precision and accuracy in measuring and estimating your roof size can go along way and save you a lot of money. Let's go back to the example in previous paragraph, which illustrates the point of making a roof measuring mistake in a metal roofing estimate; Being off by seven roof squares could easily mean that homeowner would pay $7000 extra for his new roof. This could easily be the case, if we have not told him of the true size of his roof. This goes to show how easy a homeowner can be mislead by the unscrupulous quote on quote roof estimating professionals.

Learning Objectives

This easy 4 step "do it yourself roof estimation guide" will show you how to figure out the number of roofing squares on your house, and teach you some basic pricing considerations for the common roof types.

Knowledge is power

Keep in mind that the purpose of this post is to arm you with the leverage of knowing what your roof estimate should be close to. (As in ballpark figure)
Knowing your roofing coverage size and scope of difficulty involved in re-roofing will insure that you are not taken advantage of by some dishonest contractor, or taken for a ride by his smooth talking salesman.

Fears of the unknown - why it helps to know more about your roof:

After all, we all dread, being taken advantage of by somebody who knows more than us about a specific field, and may use that power against us. Especially when stakes are high such as in the case of a leaking roof, when you may be under tremendous pressure trying to figure out what contractor to hire and how much you should really pay for the new roof. It is quite easy to find yourself caught off guard, unless of course you are well prepared.

Step 1: Measuring Your Roof.

First and foremost, we need to measure the roofing coverage surface area, which is measured in roofing squares.

Understanding roofing squares:

There seems to be a lot of confusion about a simple roofing concept called roofing square. There are exactly 100 hundred square feet in one roofing square. For example, a 10 by 10 feet area will give you exactly one square of roofing surface.

How to take roof ground measurements:

The very first thing we need to obtain the ground level dimensions of the house, or its perimeter. We can use a measure tape to obtain the length and width of the outside house walls. Later we can multiply width times the length to figure the floor level area of the house in square feet. After performing this easy multiplication we have the number that gives us a plain level area underneath the roof, in square feet. Keep in mind that we need to consider roof over hangs when taking the measurements to increase accuracy and reduce errors during calculation of the roof size.

Keep in mind that houses rarely come in perfect rectangular forms, and oftentimes buildings will have funky architectural twists. So, if your house resembles a complex geometrical figure, such as several pieces of domino pieces next to each other on the table, then we can find the areas of each respective piece first, and then add the sums of their areas in order to get a total area in square feet.

As an example suppose we have a rectangular house, which is 50 feet long and 30 feet wide, after multiplying both sides we get 1,500 square feet for the area of the house.

Step 2: Converting Roof Area to "roofing squares".

In the roofing industry we like to keep things simple and work with small numbers, that is why we want to convert our large numbers, expressed in square feet of roofing surface, to a simple number in expressed in the # of roofing squares.

Converting of the area in square feet to roofing squares is accomplished by dividing the total raw area we obtained in multiplication, by a 100. For example, if we were to divide 1500 square feet area by 100, then we get a surface area size of 15 squares for ground measurements.

Slope adjustment - Roof Pitch Multiplier

Now that we have derived our 2 dimensional ground roof measurements, we will now want to convert them to 3 dimensional roof measurements to account for the rise of the roof. This is a step in which a lot mistakes can be made, especially when dealing with a complex roof. Let me show you an easy way to minimize mistakes when performing a calculation of roof slope / steepness adjustment in order to figure out approximate actual surface of your roof.

How to Figure Your Roof's Pitch:

In this section I am going to show you how to easily determine your roof pitch, which is also known as roof slope, or steepness/rise of your roof. For simplicity purposes, I am going to classify roof slopes into three basic categories:



Step 3: Determining your Roof Pitch.

Low Roof Pitch/Slope

This type of roof would have at least a 3:12 pitch, which means that a roof rises 3 feet for every 12 feet of its base horizontal length. This type of roof is considered to be "walkable", and easy for performing a roof installation.

Note, for our purposes, low pitch roof will not be greater than 5:12 slope/steepness of the roof.

Approx. average roof multiplier: anywhere from 1.15 to 1.25 times the number of ground squares

low pitch roof
Medium Roof Pitch/Slope

The roof of this type would fall within 6:12 - 9:12 roofing slope range. Medium sloped roofs require special equipment such as roofing jacks, and planks in order to be able to perform the roofing installation. Because roofs with intermediate pitch / average slope roofs are considered to be non walkable, as they represent a higher degree of complexity, therefore they are more expensive to install.

Approximate roofing multiplier: anywhere between 1.25 to 1.4 depending on the steepness of the roof's slope, and how complicated / cut up the roof in question is. The greater the number of dormers, valleys, and endwalls, the more cut up/complex our roof is.

Medium pitch slope roof
High/Steep Roof Pitch/Slope

Roofs in this category have a slope that is greater than 9 inches of rise for every foot of horizantal roof's run.

Approximate roofing multiplier can range from 1.41 for a simple gable roof up to 1.7 for a high slopped and cut up roof. In some cases, roofing multiplier can be even greater. Perhaps, you could use a 1.5 multiplier value to calculate the surface of a high and slight to moderate cut-up roof.

The high slopped roof is, perhaps, the most difficult and dangerous roofing surface to work on. You may expect to pay a higher price for this type of roof per square of installation. Any roof, and especially steep roofs require the use of a special protections and fall arrest equipment.

high pitch roof/steep roof


Step 4: Multiply the number of ground level Roofing Squares by a roofing multiplier.

For example, let's assume that our roof has a medium pitch of 6:12, and is moderately cut up with an end-wall, and 2 valleys. So we decide to use a middle of the road multiplier factor of 1.35, remember that our average values could range from 1.25 to 1.4 as per table above for medium pitched roofs.

Let's go back to our earlier example where we have a simple rectangular shaped house that measures 30 by 50 feet, which equals to 15 roofing squares. We will now multiply that number of 15 ground level roof squares by a roofing multiplier of 1.35, which equals to approximately 20 squares of actual roofing surface.

The good news is that the rest is easy! The bad news is that it may also be pretty scary, but knowledge is power!

Now that we know our roof size in squares and have a good understanding of the level of difficulty to install a new roof, we can easily estimate how much it may cost to install a new roof on our home.

The actual roof prices will largely depend upon what the contractor charges and your negotiations skills. The prices you may expect to pay will be somewhat different depending on the company you are working with...

As a some sort of general guide line; I am going to throw in some numbers with the intent to show the calculation process and not the bottom line.

Lets assume that our house has 2 existing layers of asphalt shingle that require a complete tear off, clean up, and waste removal, which will run us $150.00 per roof square.

Now let us assume that a professional roof installation will cost $300.00 per square for material, labor and the warranty.

Thus, we have: 20 squares, times 150 = $3,000.00 for the tear off and clean up. Now we just have to add up the installation cost, which is 20 times 300, which equals to $6,000.00.

Finally, we add results, $3,000 + $6,000 = $9,000 total for the tear of and installation of a new asphalt shingle roof.

Having read and practiced the steps outlined in this Do it yourself roof estimating guide, and learning the practical steps of how to measure your roof, you should now have a better understanding about your own roof, be able to figure out its approximate actual size in roofing squares, and define the level of difficulty involved in the roof replacement. I firmly believe that knowing these easy skills is going to provide more benefits for you, than some roof calculator software spitting the mystical numbers at you.

I wish you best of luck in getting a great quality roof at a fair price!

Legal Disclaimer:

The roofing multiplier figures provided in this post are not meant to be interpreted as the absolute accurate measures, but rather they are just some mere guess-estimate values, that were arrived at through author's experience with estimating roofing jobs, and through using the, sometimes, necessary number allowances. There are many highly complex roofs where exact roof calculations may be difficult, or even impassible to perform. As such, all the figures above are to be used for your entertainment purposes only, and to be considered as not particularly reliable. They cannot be considered legally binding, valid, or used in the court of law.

Information on this page is for your entertainment purposes only, and is not based on scientific data, or some other authoritative source.













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