How to Calculate Roof Pitch and Roof Material

How to Calculate Roof Pitch and Roof Material


Are you ready to do some math?  Don’t worry, because few people ever really feel ready to do math.  It is unfortunate for many of us that roof measurement requires some math.  However, finding both the pitch and how much roofing you need does not need to be difficult.  In the following, you will see how to determine the pitch of your roof, and next, how to find out how much roofing you need to fully replace your roof.

In order to find out the area of the sides of your roof and the pitch, you will need a ladder, a level, and a tape measure.  If heights worry you, then that’s OK.  You can find the pitch from inside your attic.  It is even possible to find both the area of the sides of your roof and the pitch, or slope, from the ground.  However,  many people consider the forthcoming method to find the pitch the most accurate.  This method method is to measure the slope from the rafters.  Here is how you find the pitch:

  1. Decide which rafter to use.  You can use a rafter from the inside of your attic.  Or, you can use the overhanging rafter from the end of your house.
  2. Put the level on the underside of the rafter, so that if the rafter makes a triangle at the base, the level is at the base.
  3. Find the twelve-inch mark on the level.
  4. Measure from the twelve inch mark up to the rafter.
  5. Finally, find the ratio of the rise, the vertical distance, to the run, the horizontal distance.  Usually, this ratio is enough.

Now, to find the area of the sides to your roof, the best way is to climb onto your roof.  From on top of your roof, you measure the sides, and then you find the area.  In general, you can include flashing, skylights, and other features.  However, you want to measure dormers separately.  There are three kinds of roofs, and they are Gabled Roofs, Hipped roofs, and domed roofs.  Here is how you find there area of each:

  1. Gabled roof:  Finding the measurements of a gabled roof is the easiest.  A gabled roof has two opposite slides that slope downward.  To find the area, you simply multiply the length, the vertical side, by the width, or the horizontal side.
  2. Hipped roof:  Hipped roofs are those roofs are those roofs that angle upward at all four sides.  Another way of looking at it is that hipped roofs have shingles on all four sides.  Finding the area for a hipped roof is slightly more involved.  However, it is doable.  For a hipped roof, you find the area of the triangles on the outer sides and the trapezoid on the longer sides.  The area of a triangle is one-half the base times the height.  Or, multiply the base by the height and divide that in half.  As for finding the area of the trapezoid, what you do is add the length of one base to the length of the other base, divide that number in half, and then multiply that number by the height.  Written as an equation, it looks like this: A= ((B1+B2)/2) x H.
  3. Domed roof:  Domed roofing is more complicated.  Its generally best to hire a professional to measure domed roofing.  However the general idea is that you find the area of half a sphere.  To find this area you multiply pi by the base squared plus the height squared

Check out our blog about roof replacement cost


Leave a Reply

  • (will not be published)