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. |