🌊 Roof Valley Calculator — Linear Feet & Flashing
Free valley flashing calculator — open, closed-cut & woven valleys
Smart Roofing Calculator — Roof Valley Calculator — Linear Feet & Flashing — smartroofingcalculator.com/valleys/ — printed
🛠️ How This Calculator Works
Enter valleys and average length. The calculator applies pitch factor, overlap, waste, and estimates pieces.
📐 Formula
Total Valley LF = Valleys × Length × Pitch Factor × (1 + Waste%) + Overlap📝 Example Calculation
4 valleys × 15 ft × 1.12 pitch + 10% waste = 73.9 ft → 8 pieces
💡 Pro Tips from Roofers
- Install ice & water shield full length of every valley.
- Use chalk line to keep flashing centered.
- Nails at edges only — never through center.
- Open metal valleys are easiest to clean.
❓ Frequently Asked Questions
How do I measure roof valley length?
Measure from eave to ridge where two slopes meet, then multiply by pitch factor.
What type of valley flashing should I use?
Open valleys use metal flashing (W-valley). Closed-cut valleys weave shingles. Open metal is most durable.
How wide should valley flashing be?
Standard W-valley is 20-24 inches wide. Use 24" minimum in heavy rain/snow areas.
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📝 Related Articles
About the Smart Calculator Team
We build free, accurate construction calculators for homeowners and contractors. This article is part of our roofing knowledge base — we also publish guides and tools for other home improvement projects:
Shopping for someone? See our gift guide for roofers & DIY homeowners.
🔗 Related Roofing Calculators
- Underlayment & Ice & Water Shield Calculator — Required full-length under every valley
- Roof Flashing Calculator — Step, wall & chimney flashing
- Shingles Calculator — Add 5–10% waste for valley cuts
- Roof Pitch Calculator — Pitch factor for true valley length
- Chimney Flashing Calculator — Step, apron, cricket & counter flashing
Where two roofs meet, the valley rafter calculator gives the valley length and valley jack rafters, even for unequal pitches.
Adding the ridge cap to the order? See ridge cap and valleys estimate.
· Reviewed by the Smart Roofing Calculator editorial team