Accurate roof measurement is the foundation of any cost estimation. While ground-level square footage provides a baseline, professional roofing estimates must account for three variables: Slope (Pitch), Complexity (Waste), and The “Square”.
1. Defining “The Roofing Square”
Roofing materials are sold by the “Square,” not the square foot.
$$1 \text{ Square} = 100 \text{ Square Feet}$$
2. The Pitch Multiplier
A steep roof has significantly more surface area than a flat roof covering the same footprint. We apply a Pitch Multiplier to correct this.
| Pitch | Multiplier |
|---|---|
| 4/12 (Low) | 1.054 |
| 6/12 (Moderate) | 1.118 |
| 8/12 (Steep) | 1.202 |
| 12/12 (High) | 1.414 |
Formula: $$ \text{Actual Area} = \text{Base Footprint} \times \text{Multiplier} $$
3. Waste Factors
You must order extra material to account for cutting shingles at valleys, hips, and ridges.
- Gable Roof: +5-7% Waste
- Hip Roof: +10-12% Waste
- Complex: +15-20% Waste
4. Example Calculation
For a 2,000 sq. ft. footprint home with a 6/12 pitch and standard waste:
- $$2,000 \times 1.118 = 2,236 \text{ sq. ft. (Actual Area)}$$
- $$2,236 \times 1.10 \text{ (10\% Waste)} = 2,460 \text{ sq. ft.}$$
- $$2,460 / 100 = \textbf{24.6 Squares}$$