There are two ways to estimate the total number of squares that are installed on
the roof. One way includes measuring the area of the house footprint and multiply
that by a roof slope factor. Another way includes measuring the area of each
plane on the roof and add them all together. In this video, we're going to
learn how to measure each plane of the roof to calculate the total square
footage. To do this, you have to measure the length and width of each plane on
the roof including the dormers then multiply length by width to get the
square footage of each plane finally calculate the roofs total square footage
by simply adding the square footage of each of the planes together there are
several different styles of roofs including shed roofs hip roofs
and gable roofs this is a shed roof a shed roof has one roof plain simply
measure the length of a then measure the length of B now the area of the shed
roof is a times B which is in this example twelve and a half feet times
twelve and a feet which is 156 in a quarter square foot for the total square
footage of the shed roof this is a square the area of a square is simply
base times height in this example the base is twelve and a half and the height
is twelve and a half this is a rectangle the area of a rectangle is just like a
square it is base times height and in this example the base is 15 feet and the
height is 12 and a half the area of the rectangle is therefore 15 times 12 and a
half which equals 180 seven and a half square feet
this is a gable roof a gable roof has two planes so multiply the base times
the height for each plane or rectangle to get the square footage for each plane
then add the two rectangles together to get the total square footage of the roof
so let's assume one rectangular plane of the roof is sixteen by 40 and the other
plane is sixteen by 40 the area of each plane is 16 times 40 equals 640 square
feet by adding the two rectangular planes together the total square footage
of the roof is 1280 square feet this is a hip roof now a hip roof has four
planes and they are not rectangular like the other roofs so you'll need to know
some simple geometric formulas to calculate areas of roof shapes including
trapezoids and triangles a hip roof will include a trapezoid shape to calculate
the area of a trapezoid you add the length of each base base one plus base
two and then multiply it by height then you divide that by two to get the square
footage of the one trapezoid plane in this example one of the hip roofs
trapezoid planes is 10 plus 15 times 12 equals 300 divided by 2 equals 150
remember that's just for one of the trapezoid shapes of the hip roof in this
example there are two trapezoid shapes in the illustration you can see this hip
roof has two trapezoid shapes and two triangle shapes so let's look at
calculating the area of a triangle the area of a triangle regardless of the
triangle shape is base times height times 1/2 in this example the area of
the triangle is 8 feet times 10 feet times one-half equals 40 square feet the
four planes of a hip roof include two triangles and two trapezoids
calculate the area of each shape and add them all together to get the total
square footage of the hip roof area there are several different types of
roofs and their area calculations
let's take a complex house roof as an example and calculate its total square
footage this complex roof has lengths of various geometric shapes of the roof
measured the main house roof is a large gable roof looks like the front entry
has a small gable roof the rear deck has a hip roof there and there's a gazebo
roof attached to the back of the house let's calculate the area of this complex
roof in total square footage let's start with the red octagon a4 which is just
like a bunch of triangles stuck together we know that the area of a triangle is
base times height times 1/2 so the octagon is 8 of those triangles added
together so if the base is 5 feet and the height is 6 the area of the octagon
is 8 times base times height times 1/2 and it equals 120 square feet now let's
look at the yellow shapes the area of the east gable a3 is the addition of 2
trapezoids we know that the area of a trapezoid is base one plus base 2 times
height times 1/2 so for this house the east gable a3 is 16 feet 3 inches plus
10 times 5 which is height times 1/2 but because there are two trapezoids you
double that amount to get the total square footage of the east gable roof in
yellow the west gable roof is measured by calculating the area of one of the
trapezoids and then doubling it to get the total square footage it's the same
method we used for the East gable roof next is the big blue section a gable
roof with two large rectangular Plains we know that the area of a rectangle is
base times height for this house roof we have base times height as 10 times 60 or
600 square feet there are two rectangular planes the
total square footage of the blue main house roof a 1 is double that 1200
square feet due to the overlap in areas we must subtract a portion of each
yellow gable from the main house roof total so the green dashed lines indicate
the areas that must be subtracted from the main house roof a 1 here's the
breakdown of all the shapes and their areas
you
when you add up all the shapes the total roof area is 1820 square feet now
convert the total square footage to roofing squares in roofing terminology a
square is 100 square feet now divide the total area by 100 so 1820 square feet
that's the total area of the entire house roof divided by 100 equals 18.2
squares this answer is the number of roofing squares for the roof 18.2 so in
summary we learned how to calculate the size of a roof by measuring the total
square footage of the roof and dividing that by 100 remember the area of a
square is simply base times height the area of a rectangle is just like a
square base times height the area of a triangle is base times height times 1/2
the area of a trapezoid is base one plus base two times the height times 1/2 and
a square in roofing terms is 100 square feet