# How to Estimate Roofing Materials

Three Parts:Estimating ShinglesEstimating Felt Underlayment (Tar Paper)Estimating Other Materials

If you are adding an additional layer to existing roofing, you’ll only need to worry about estimating the amount of shingles and nails. If you are replacing old roofing or roofing a new structure, you’ll need to estimate roofing materials such as felt underlayment and drip edge. To do all of this, you'll need to understand how to translate measurements into bundles of shingles for a more accurate estimate of roofing materials to order.

## Steps

### Part 1 Estimating Shingles

- 1
**Find the square footage of the roof.**Measure the length and width of each portion of the roof, multiply length by width for each plane, and then add the planes together for the total square footage. - 2
**Determine the total number of squares.**Divide the total footage by 100 to determine the number of “squares” in the roof. - 3
**Determine the bundles of shingles needed to cover the roof.**It takes 3 bundles to cover a square if you use 3-tab shingles, the most common type. - 4
**Account for waste.**Add 10 percent to the shingle estimate to account for waste.- If your roof has hips and valleys, make it 15 percent because of waste in cutting shingles to fit the valleys.

### Part 2 Estimating Felt Underlayment (Tar Paper)

- 1
**Find the square footage of the roof.**Measure the length and width of each portion of the roof, multiply length by width for each plane, and add the planes together for the total square footage. - 2
**Find the number of squares.**Roofers measure surfaces in squares of 100 feet (30.75 square meters). Divide the total footage by 100 to find the number of squares in the roof. - 3
**Determine the number of rolls of underlayment needed.**The #15 type is most commonly used, and one roll of #15 underlayment covers 4 squares.- If you’re using #15 underlayment and your roof slope is greater than 4:12, use 1 layer. If the slope is between 3:12 and 4:12, double the amount and put down 2 layers.

### Part 3 Estimating Other Materials

- 1
**Measure for drip edge.**This metal strip, which goes beneath the underlayment, protects the edge of the roof from rot. You'll need the measurements of the rakes and eaves of the roof (side edges and bottom edge). - 2
**Estimate how many roofing nails you'll need.**At 4 nails per shingle, that’s about 320 nails per square.- For high-wind areas, use 6 nails per shingle, or 480 nails per square.
- Inquire at the hardware store regarding the size of nail you’ll need and how many pounds you’ll need of that size; the number of nails per pound differs. The nails should be long enough to go ¾ inch into the roof.
- Inquire at the hardware store regarding the amount of underlayment nails required. Use ¾-inch (1.8 cm) nails if the roof deck is ½ inch (1.2 cm) or 1-inch (2.5 cm) nails if the roof deck is 5/8 inch (1.6 cm) or greater. The nails should be 12 inches (30 cm) apart along the edges and 24 inches (60 cm) apart in the middle of the underlayment strip.

- 3
**Gauge the amount of hip and ridge cap shingles.**While you can order special hip and ridge cap shingles, you can make your own by cutting a 3-tab shingle into 3 pieces. A bundle of 3-tab shingles will cover 35 lineal feet (9.2 m).

## Sources and Citations

## Article Info

Categories: Exterior Walls and Roof