How to Install a Roof

Calculating Roofing Materials

The first thing to know is that if you order shingles based solely on the Squares or Square foot area of the roof, you won’t have enough. You will need shingles for starter courses along the eaves and at some rakes, and you will need shingles to cap hips and ridges. You can cut shingles to use as these caps, ridges and starter, as well as cutting at the rakes, against walls and chimneys, and at valleys. This cutting will always cause some waste. Some of the cutoffs will be big enough to use as starter shingles or in other areas where cut shingles are needed, but smaller cutoffs will be waste. Waste can vary from 1-5% depending on the complexity of the roof.
    The only roof that will generate no waste from cutting is a simple gable roof whose length is divisible by the 3-ft. length of a shingle.
Starter Shingle - is the shingle at the 'bottom edge' of the roof with the exposure portion trimmed off, leaving just the self-seal strip and top lap. They are fastened along the eaves edges to seal down the first course of shingles and provide coverage material beneath the tab cutouts just like the top lap of each successive course.

Starter Shingle Example

You calculate starter from the parameter measurement, the same as the Drip Edge generally

    Parameter Linear Feet/120 = # of Bundles of Starter for 20 year

    Parameter Linear Feet/80= # of Bundles of Starter for 30 year

Ridge - there are various types, like rapid ridge which provides stronger ridges that are further resistant to damage, stand slightly higher and look nice on your roof cap lines. However in most cases regular shingles are cut to be used as ridge.
  • Rapid Ridge is usually 20LF per box
  • Standard Ridge (cut shingles) can cap 35 lin. ft. of ridges and hips with each bundle of shingles.
    Calculating Ridge
  • Hip + Ridge = Ridge Needed
  • Linear Feet/33 = # of bundles needed for ridge
  • *Ridge Vent use 9in for 30 year shingles

Drip Edge
    Linear feet/10 + 5 = Drip Edge Needed (1 1/2 x 1 1/2)
    Linear feet/33 = # of rolls needed
    Number of Squares/4 = # of rolls of 15# felt needed
    Number of Squares/2 = # of rolls of 30# felt needed
    1 box per 20-25 squares
    Step Flashing (include at least 1 per job?

Roof Pitch Calculation
    Roof PitchRoof Pitch Multiplier

    Example calculations:
    Roof is 8/12 pitch and measures at 1900 square feet
    1900 x 1.2= 2280
    2280 - 1900= 380 feet added for pitch

    If the home measures 20 X 40 and has a 7:12 roof, then to calculate the slope of the roof follow these steps:
    Step 1: Multiply 20 and 40 which equals 800.
    Step 2: Find the value of 7:12 from the roof slope multiplier table which is 1.16.
    Step 3: Multiply Step 1 and Step 2, i.e. 800 multiplied by 1.16.
    Step 4: The value arrived at, 928, reflects the square feet of the roof.