Estimating how much roofing and gutter materials you need is very simple. The only thing you need to do is to calculate the number of squares in the roof surface. One square equals 100 square feet so just do your math. Some roofs provide for easier math than others. For a simple roof with unbroken planes for example, you will need to figure out the surface area of each side by multiplying the length by the width and then adding the two sums. Once you have done this, divide it by 100. Always remember to round it off to the next highest figure. Some roofs and gutters with more of a complex structure or steeper roof will provide more of a challenge. The best thing to do here is to measure the square footage of the actual house at ground level and then take into account the slope of the roof. Say that you have a house and garage that you want a new roof on. Your house measures 1200 square feet at ground level and has a roof with a 4 in 12 slope. Your garage measures 300 square feet and has a roof with a 6 in 12 slope. By using the table below you can easily estimate your roof surface.
Slope: Multiply by:
2 in 12 1.02
3 in 12 1.03
4 in 12 1.06
5 in 12 1.08
6 in 12 1.12
7 in 12 1.16
8 in 12 1.20
House: 1200 square feet x 1.06 = 1272 square feet.
Garage: 300 square feet x 1.12 = 336 square feet.
Total roofing area: 1272 + 336 = 1608 square feet divided by 100 = just over 16 squares.
As with most things in life, if you are not sure of doing this yourself – you can always hire a professional and leave the work and calculations to them. If you are estimating your own roof surface, remember to take into account anything on the roof that is not actual roof surface. Things like chimneys, dormer windows, skylights, overlapping roof planes or overhangs at the eaves has to be taken into account when you are calculating your roof surface as this means you will need less material as it takes up some of the roof surface. However, it is always better to order a little bit too much material than not enough as it can otherwise cause a delay of the work.