How to Estimate the Height of a Roof

Place an angle finder against the underside of a roof rafter according to the manufacturer's instructions. This device generally measures the angle between the angle finder's current orientation and the horizontal plane. Record the reading on the angle finder to obtain the angle of the roof. Assume for this example that the roof angle is 24 degrees.

Make a mark at eye level on an outer wall at one end of the house. Measure the distance of the mark from the top of the outer wall with a tape measure. Assume for this example that the mark is 3 feet below the top of the outer wall. Use the tape measure to make a mark on the opposite outer wall at the same height.

Measure the distance between the two marks that you made in Step 2 to obtain the distance between the outer walls on one end of the house. This distance is also known as the span of the roof. Assume the roof span is 30 feet in this example.

Divide the roof span by two to obtain the run of the roof. The roof span is 30 feet, so the run of the roof is 30 / 2 = 15 feet.

Multiply the tangent of the roof angle by the run of the roof to obtain the rise of the roof. The roof angle in this example is 24 degrees, and the run of the roof is 15 feet. The rise of the roof in this example is therefore tan (24) x 15 = 6.68 feet.

Measure the height of the outer wall with a tape measure. Assume the height of the outer wall is 8 feet in this example.

Add the rise of the roof to the height of the wall to obtain the height of the roof. The rise of the roof is 6.68 feet, and the height of the wall is 8 feet, so the the height of the roof in this example is 6.68 + 8 = 14.68 feet.