| There are many ways in which to measure a roof. This
section will show one method of how to properly do it. We’ll express our final answer
in "squares". In all roofing except polyurethane foam, roofers express Area in
"squares". 1 square = 100 square feet
Before you get started, you need to know some simple geometry.
The base length (b) times the height (h) of any triangle is twice
its area (A). So if you divide the product of the base and height by two, then you have
the area of a triangle.
(b×h)/2 = Area
Therefore, the following two triangles, R and H, though different in looks and shape, have the exact same area.
(20' × 20')/2 = 200 square feet
Now that you know this simple mathematical fact, you will easily
understand how to measure the following roof.
The picture shown is an aerial view of a roof with both a hip end
and gable ends. It is strongly recommended that you make a rough sketch of your roof. In
order to make it easier for measuring, the roof will be broken up into sections A through
F.
Section A
This section is a simple triangle. Simply measure the length of the
eaves and the perpendicular line from the eaves to the peak. Multiply these numbers and
divide the answer by two.
(30' × 15')/2 = 225 square feet
So Section A has 225 square feet in it.
Section B
The easiest way to measure this section is to divide it up into
three different sections: x, y, and z. It’s pretty obvious that
sections x and z are the same size, even without
being marked. But because it’s much easier to work in theory and numbers on pieces of
paper (like architects do) than actually performing the construction (like contractors
do), it’s always a good idea to go ahead and measure both triangles.
x = (15' ×
15')/2 = 112.5 square feet
y = 55' ×
15' = 825 square feet
Because we know that z is equal to x after measuring, we’ll simply add another 112.5 square feet to our
current list of numbers.
So Section B has a total of 112.5 + 112.5 + 825 = 1,050
square feet.
Section C
Again, with this section it’s pretty obvious that we have
symmetrical sides. Let’s go ahead and divide it up into sections, measure one side
and get the answers that we want and then we’ll check the other side.
w = 30' ×
15' = 450 square feet
y = (15' ×
15')/2 = 112.5 square feet
A quick measurement verifies that x and z are the same as w and y so
we’ll multiply the sum of w and y by
2 for the final Area.
Section C = (450 + 112.5) × 2 = 1,125 square feet.
Section D
x = (15' ×
15')/2 = 112.5 square feet
y = 10' ×
15' = 150 square feet
Section D = 112.5 + 150 = 262.5 square feet
Section E
This section has several different subsections so we’ll have to
be careful and make sure we do it right. If your roof has a section similar in shape,
double check your sketch to make sure that every piece is either rectangular or
triangular.
s = (15' ×
15')/2 = 112.5 square feet
t = 40' ×
15' = 600 square feet
Remember to check both small triangles in the center part to make
sure that they are the same size.
x = (10.5'
× 10.5')/2 = 55 square feet
y = 21' ×
4.5' = 94.5 square feet
The actual answer of x is 55-1/8 square feet, but we rounded off for ease of measuring.
z = 34' ×
15' = 510 square feet
Be careful adding all of these up. Remember that there are two
different x sections
so we’ll need to add it twice. Section E = 112.5 + 600 + 55 + 55 + 94.5 + 510
= 1,427 square feet.
Section F
This section is simply a smaller version of Section C so
we’ll do it the same way.
w = (10.5'
× 10.5')/2 = 55 square feet
y = 20' ×
10.5' = 210 square feet
Don’t forget to make quick measurements to ascertain that x and z are equal to w and y.
Section F = 55 + 55 + 210 + 210 = 530 square feet.
Sum It Up
Now take all sections and add them up.
| Section A |
= 225 |
| Section B |
= 1,050 |
| Section C |
= 1,125 |
| Section D |
= 262.5 |
| Section E |
= 1427 |
| Section F |
= 530 |
Out total square footage is equal to 4,619.5 square
feet. Or, roughly 46 squares. Remember that 1 square = 100 square feet. |
