🔎 Plan Symbols

• Roof slopes: arrows with ratios (e.g., 4:12 = 4" rise per 12" run).
• Ridges: solid or bold line across peak.
• Valleys: dashed line where two slopes meet.
• Hips: diagonal lines at roof edges.
• Flashing: triangles or hatching around penetrations.
• Roof drains/scuppers: circles/squares with tags.

📐 Key Calculations

• Roof area: (building length × width) ÷ cos(slope angle).
• Squares: total SF ÷ 100 = # of roofing squares.
• Shingles: ~3 bundles per square (varies by type).
• Underlayment: matches roof area, add 10% waste.
• Pitch conversion: 4:12 ≈ 18.4°, 6:12 ≈ 26.6°, 12:12 = 45°.
• Waste factors: add 5–15% for hips, valleys, dormers.

⚡ Quick Reference

• 📏 Standard shingles: 36" × 12", 3-tab or architectural.
• 🛡️ Ice & water shield: min 24" inside exterior wall line at eaves.
• 🧱 Metal flashing: step flashing 2" × 4", counter flashing as specified.
• 🏠 Roof loads: live = 20 psf (typical res.), dead = 10–15 psf.
• 🌧️ Minimum slope: asphalt shingle 2:12 (with double underlayment).
• 🌬️ Nailing: 4 nails per shingle (6 nails in high-wind zones).

📝 Self Test

1. How many bundles of shingles are required for a 2,000 SF roof?
2. What does a dashed line in a roof plan valley represent?
3. What slope ratio is equal to 26.6 degrees?
4. How far must ice & water shield extend past the warm wall line at eaves?
5. How many nails per shingle are required in high-wind zones?

(Answers: 1) 2,000 ÷ 100 = 20 squares × 3 bundles = 60 bundles, 2) Roof valley, 3) 6:12, 4) 24", 5) 6 nails)