Virginia Class A Builder Lic# 2705158280

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Roofing and Gable Calculations

Calculating Bundles of Roof Covering

  1. Measure Height from the bottom of the roofline to the ridge board.
  2. Measure the Building Length ( include the overhang )
  3. Multiply Length by Height for the area.
  4. Divide total area by 100 ( this is the number of squares required )
  5. Multiply the squares by the number of bundles per square (or see the table Below, or manufactures instructions for quantity)

Coverage Area per Roll of Felt (Underlayment)

  1. 15# Felt Underlayment 400 SF
  2. 30# Felt Underlayment 200 SF

Waste Factors

  1. Simple roofs (Gable) ---1 - 5%
  2. Complex roofs -----------5 - 10%

Gable Calculations

Calculating the Run of a Building
Run = Span ÷ 2		 Example: What is the run of a building that has a 50' span?
1. Run = Span ÷ 2
2. Run = 50 ÷ 2
3. Run = 25
Calculating the Gable Height of a Building
GH = Run x Vertical Rise		 Example: What is the run of a building that has a 60' run? The Slope is 6:12
1. Run = 60 ÷ 2
2. Run = 30
3. GH = Run x Vertical Rise
4. GH = 30 x 6
5. GH = 180" (or 15')
Calculating the Gable Area of a Building
GA = Gable Height x Run		 Example: What is Square Feet in the Gable Area of a 50' wide building with a 12' Gable Height?
1. GA = Gable Height x Run ÷ 2
2. GA = 12 x 25 ÷ 2
3. GA = 150 SF

Gable Height

Calculating Common Rafters on Hip / Valley

NOTE: This works for hip and gable roofs.

  1. Measure the run (Flat dimension).
  2. Identify the multiplier that corresponds with the roofs slope.
  3. Multiply the run by the multiplier.
  4. Round to the next "even" number.

Calculating Roof Area from Plans

NOTE: This works for hip and gable roofs.

  1. Add the overhang to dimensions.
  2. Multiply Length by Width.
  3. Multiply the area by the rafter multiplier that corresponds with the roof slope of your plans.
  4. Divide by 100 to calculate the number of squares.