Roof Types & Terminology
Roof styles, slope terminology, a square in roofing, sheathing types, and structural components.
- Define a 'square' in roofing terminology and calculate roof area in squares
- Identify common residential roof styles including gable, hip, mansard, and butterfly
- Explain the minimum slope requirements for asphalt shingles
- Describe the types and minimum thickness of roof sheathing
- Recognize the function of plywood clips in roof sheathing
Leçon 1
Slope Measurement & Roof Geometry
Understanding Roof Slope
Roof slope is expressed as the rise over a 12-inch horizontal run. A roof with a 4:12 slope rises 4 inches for every 12 inches of horizontal run. Understanding slope is critical because it determines which roofing materials can be used and how they are installed.
The minimum roof slope for asphalt shingles is 4:12 (18.4 degrees). Shingles installed on slopes below 4:12 require special low-slope application methods with additional underlayment. Below 2:12, asphalt shingles cannot be used at all.
The Roofing Square
A square in roofing terminology is 100 square feet of roof area. This is the standard unit for estimating and ordering materials. To calculate the number of squares:
- Measure the roof area in square feet (length x width for each section)
- Divide total area by 100
- Add 10-15% for waste, depending on roof complexity
For example, a simple gable roof measuring 40 feet x 30 feet = 1,200 square feet = 12 squares. A hip roof requires more waste allowance due to the angled cuts at hips and valleys.
Exam Tip
When the exam asks "What is a square in roofing?" the answer is always 100 square feet of roof area. This applies regardless of the roofing material being installed.
Steep Slope vs. Low Slope
Roofs are classified by slope into two categories:
| Classification | Slope Range | Common Materials |
|---|---|---|
| Steep slope | Above 4:12 | Shingles, metal, tile, wood shakes |
| Low slope | Below 4:12 | BUR, modified bitumen, single-ply membranes |
| Flat | 1/4:12 minimum | BUR, TPO, EPDM, PVC |
The typical pitch for a steep slope roof is between 4:12 and 12:12. Steeper pitches shed water faster but are more difficult and dangerous to work on.
A square equals 100 square feet of roof area. The minimum slope for asphalt shingles is 4:12 for standard installation, and 2:12 with special low-slope methods. Below 2:12, membrane roofing systems must be used instead.