Roof valleys are critical transitions where two roof planes meet and channel water away from the roof. Using asphalt shingles, one of the most common roofing materials in the United States, requires careful detailing to prevent leaks and ensure durability. This guide explains valley design, installation options, maintenance, and best practices to help homeowners and contractors achieve reliable performance with asphalt shingles.
What Is A Roof Valley?
A roof valley is a channel formed where two roof slopes intersect. Water flows into the valley and down to the eaves. Proper valley construction is essential to prevent water intrusion, ice damming, and shingle damage. Valleys must shed water efficiently while withstanding wind uplift and temperature fluctuations. In asphalt shingle systems, valleys must be integrated with flashing, shingle placement, and flashing membranes to create a continuous, waterproof path.
Valley Types For Asphalt Shingles
There are several valley configurations used with asphalt shingles, each with its own advantages and installation nuances. The most common types are open valleys and woven (closed) valleys. Open valleys leave a metal or synthetic metal lining exposed as the valley channel, while woven valleys weave shingles over themselves to form a continuous surface that hides the flashing. A third option, partial open or shingle-stamped valleys, blends features of both methods for particular roof lines and climate conditions. Choosing the right type depends on roof design, climate, and professional recommendations.
Open Valley Vs Woven Valley
Open valleys provide a clear water path and can be easier to inspect. They typically use a metal valley flashing installed under the shingles, with shingles lapped over the flashing. This method is common on colonized roofs and areas with heavy rainfall. Woven valleys offer a cleaner look and extra protection by weaving shingles into the valley, which can reduce visibility of flashing. However, they require precise cutting and overlap to avoid gaps. In icy regions, the exposed flashing in open valleys can help with ice dam prevention, but improper installation may lead to leaks if flashing penetrations fail.
Installation Steps For Asphalt Shingle Valleys
Proper installation begins with accurate measurements and material preparation. The following steps outline a typical approach for asphalt shingles on valleys, whether open or woven, and emphasize waterproofing and wind resistance.
- Prepare the roof deck: Inspect for dry, clean sheathing. Replace damaged boards and install drip edge along eaves and rakes.
- Install valley flashing: For open valleys, install metal flashing along the valley centerline, ensuring it overlaps under the shingles on each side. Seal fasteners above the waterline when possible. For woven valleys, flashing is typically installed under the shingles to remain hidden, with careful shingle alignment at the valley.
- Lay starter courses: Begin with a modular starter strip at the eaves, extending appropriately across the valley. Stagger joints to reduce leaks and ensure wind resistance.
- Cut and install shingles: Trim asphalt shingles with precise angles at the valley edges. For open valleys, shingles should extend over the flashing with a clean, straight edge. For woven valleys, carefully weave the edge shingles to cover the valley without gaps.
- Seal and fasten: Use the recommended asphalt adhesive or roof cement to seal shingle tabs near the valley edges. Place roofing nails below the adhesive line and maintain the manufacturer’s nailing pattern.
- Inspect water flow: After installation, run a water test or check with rainfall after the first major storm. Look for flashing leaks, lift, or pooling in the valley.
Maintenance, Repairs, And Common Issues
Regular maintenance helps extend valley life and prevent leaks. Key practices include cleaning debris, inspecting for damaged shingles, and resealing flashing where necessary. Common issues include lifted shingles due to wind, cracked valley flashing, and shingle blow-off at valley edges. Early detection is crucial; address loose or damaged elements promptly to avoid costly water intrusion. In areas with freeze-thaw cycles, ice damming can stress valley seams, so consider supplemental insulation and heat cable strategies where appropriate.
Material Quality And Best Practices
Choose shingles and flashing from reputable manufacturers with proven performance in the local climate. For valleys, ensure flashing is corrosion-resistant and compatible with asphalt shingles. Use continuous, properly sealed valleys to prevent water intrusion. Best practices include: staggering joints, using appropriate fasteners, following shingle warranty guidelines, and ensuring proper ventilation to minimize condensation near valleys. Thoroughly read installation manuals, and if in doubt, consult a licensed roofer to verify valley details for the home’s roof pitch and layout.
Safety Considerations And Professional Involvement
Roof work is hazardous, and valley work involves tools, heights, and weather exposure. Always prioritize fall protection, ladder safety, and weather awareness. For complex roof geometries, tall structures, or multi-story homes, hiring a licensed contractor with experience in asphalt shingle valleys reduces risk and improves outcomes. While DIY can be feasible for simple, well-covered roofs, professional installation ensures compliance with building codes and warranty requirements.
Cost Factors And Longevity
Valley installation costs vary based on roof size, valley type, material quality, and labor. Open valleys may cost more due to metal flashing, while woven valleys require skilled labor for precise shingle weaving. Expect the valley to last as long as the roof system when properly maintained. Typical asphalt shingle roofs last 20 to 30 years, with valleys benefiting from maintenance to prevent early wear. Proper ventilation, insulation, and timely repairs contribute to extending overall roof life.
Frequently Asked Questions
Can I install valleys myself? Yes, skilled DIYers can install some valley configurations, but it requires careful attention to flashing, sealant, and safety. For complex roofs or windy climates, professional installation is recommended. Which valley type is best for ice-prone areas? Open valleys with robust flashing and heat-tracing considerations can mitigate ice dam risks, but local code and climate dictate the best choice. How often should valleys be inspected? Inspect after major storms and at least twice a year during seasonal maintenance, looking for lifted shingles, flashing damage, or debris buildup.
Key Takeaways
Valleys are essential water channels on asphalt shingle roofs. Open valleys with metal flashing offer clear water drainage, while woven valleys provide a clean look but require precision. Proper flashing installation, shingle placement, and regular maintenance are critical to prevent leaks. When in doubt, consult a licensed roofer to ensure valley systems meet local codes and warranty requirements.