Roofing is measured in squares. To figure out your roof's area, a simple geometry can be used. The key is to be as accurate as possible since falling short, or an overage could mean thousands of dollars when planning your roofing budget. Below is a simple triangle, as we will as 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, as we will as how to apply some simple math to calculate how much material you'll need for a roof used in our hypothetical example

1 roof square = 100 square feet; The length (l) times the height (h) of a triangle is twice it is area (A2). Therefore if you divide your answer of a product of length times height by two, you'll get the area of a triangle. (lxh)/2 = Area

Calculating an area of a triangle when estimating a roof

In Figure above: l=30 feet h=12 feet (30? x 12?)/2 = 180 square feet

Now that the basic concept has been covered, let's take a look at a more complex roofing system. In this overhead view you see both a hip-end section, as we will as 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, as we will as calculate your materials. For this example we will break this roof up into sections labeled A through E

A sketch of a Hip as we will as Gable Roof

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Fig. A

Calculating for a Basic Triangle of a Hip Roof

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Fig. B

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, as we will as the vertical line from the eaves half way point to the peak. Multiply these numbers, as we will as then divide the answer by two. . .


(30? x 18?)/2 = 270 square feet

a Hip Roof split in half

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Fig. C

The easiest way to measure this section is to divide it up into three different sections: S1, S2, as we will as S3. As you can see, S1 as we will as S3 are the same size, however you still need to document all measurement points to verify your material calculation accuracy. Since S2 is now a rectangle, simple L x W is all that is required

S1 = (18? x 15?)/2 = 135 square feet. .


S2 = 50? x 15? = 750 square feet. .


S3 = (18? x 15?)/2 = 135 square feet

Adding up our totals from these three sections = 1,020 square feet

An Overhead view of a Hip as we will as Gable Roof split in sections

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Fig. D

Again, we divide the roof up in sections. Measure eave to ridge as we will as rake to valley for S4 as we will as S5. S6 as we will as S7 is from eave end to valley end as we will as eave to ridge

S6 = (18? x 18?)/2 = 162 square feet. .


S7 = (18? x 18?)/2 = 162 square feet. .


Or you could add the two 18? widths getting 36 as we will as multiply by 18? length divide the answer by 2 as we will as get the same answer of 324? for both S6 as we will as S7. .


For S1 as we will as S2 we will add the total length on the rake side as we will as multiply that by the eave to get our answer. .


18' 18'=36? x 30'= 1080 square feet. .


Fig C total: 324?. 1080? = 1404 square feet

Estimating a Roof Valley, Ridge, as we will as Rake areas

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Fig. E

Here we will start with S9 18? x 10? = 180? as we will as S8 (18? x 18?)/2 = 162? for a total of 342 square feet

The last two sections are as follows: 96? x 18? = 1728? as we will as (18? x 18?)/2 = 162? for a total of 1890 square feet

Sum It Up - Total Roof Calculations:

Now, take all sections as we will as add them up. Fig A = 270 Fig B = 1,020 Fig C = 1,404 Fig D = 342 Fig E = 1890 for a grand total of 4,926 square feet. Or, roughly 50 squares. Remember that 1 square = 100 square feet

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