One roofing square equals 100 square feet. Standard shingles come 3 bundles per square. Simple roofs need 10% waste, complex roofs 15%, very complex roofs 20%. Pitch multipliers range from 1.000 (flat) to 1.414 (12/12 pitch).
Essential Tools
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View Product (paid link)📦 Underlayment Coverage
Synthetic Underlayment
#15 Felt Paper
#30 Felt Paper
Synthetic vs. Felt Paper
Synthetic underlayment covers 1,000 sq ft per roll compared to 400 sq ft for #15 felt, significantly reducing installation time and waste. Synthetic is more durable, slip-resistant, and increasingly preferred by professionals.
📊 Waste Factors by Roof Complexity
Simple Roofs
Complex Roofs
Very Complex Roofs
Extremely Complex
📐 Roof Pitch Multipliers
| Pitch | Angle (degrees) | Multiplier | Description |
|---|---|---|---|
| Flat | 0° | 1.000 | No slope |
| 2/12 | 9.46° | 1.014 | Very low slope |
| 4/12 | 18.43° | 1.054 | Low slope |
| 6/12 | 26.57° | 1.118 | Common residential |
| 8/12 | 33.69° | 1.202 | Steep |
| 10/12 | 39.81° | 1.302 | Very steep |
| 12/12 | 45.00° | 1.414 | 45-degree angle |
Formula: Roof Area = Base Area × Pitch Multiplier × (1 + Waste Factor)
Example: 1,200 sq ft footprint at 6/12 pitch with 10% waste = 1,200 × 1.118 × 1.10 = 1,476 sq ft (14.76 squares)
📚 Industry Standards
NRCA - National Roofing Contractors Association
Provides comprehensive guidelines for roofing installation including waste factors (10% simple, 15% complex), shingle application methods, underlayment requirements, and ventilation specifications per IRC/IBC.
ASTM D8257 - Synthetic Roofing Underlayment (2020)
Standard specification for synthetic roofing underlayment. Covers physical properties, water resistance, UV stability, and performance requirements. Synthetic rolls typically cover 1,000 sq ft vs 400 sq ft for #15 felt.
ASTM D225 - Asphalt Saturated Felt
Standard specification for felt paper underlayment. #15 felt weighs 34.6 lbs per 4-square roll (400 sq ft). #30 felt weighs 43.2 lbs per 2-square roll (200 sq ft).
IRC/IBC Ventilation Requirements
Building codes require 1 sq ft of net free ventilation area per 150 sq ft of attic space (1:150 ratio). Proper ventilation prevents moisture buildup and extends shingle lifespan.
Calculate Your Roofing Materials
Get precise estimates for shingles, underlayment, ridge caps, and more with automatic pitch multipliers and waste factors.
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