Just measure the length and width of each plane on the roof, including dormers. Then, multiply length x width to get the square footage of each plane. Simply add the square footage of each of the planes together to derive the total square footage of your roof.
Multiply the area by the pitch multiplier to get the roof’s square footage. First, multiply the length by the width. Then, take the product of these two dimensions and multiply it by your pitch multiplier. The number you get will be an accurate estimate of how much area you have to cover for your roofing project.
How do you find the slope on a flat roof?
For drainage purposes, the current building codes require a minimum two percent slope or a one-fourth unit vertical for every 12 units horizontal. In other words, the roof must slope one-fourth of an inch for every 12 inches. The slope is barely noticeable to the naked eye.
If your roof is too steep to navigate safely, you can use one of two alternatives. If you have an attic that you can easily access, measure the roof from the inside of the attic. Otherwise, measure the length of the roof by measuring the length of the wall that it hangs over and add a foot for overhang. Using a ladder, stand at the edge of the roof and measure the width by feeding a stiff measuring tape from edge to the peak of the roof. Repeat this for all sections of the roof, and then multiply the length and width of each section to get total square footage.