Valley detailing on fiberglass shingles is a critical step to ensure water flows properly off the roof without causing leaks. There are three common types of valley installations: woven, closed-cut, and open metal, each with specific techniques. Woven valleys interlock shingles from both sides, creating a strong barrier but requiring skill to avoid gaps where water can penetrate. Closed-cut valleys involve layering shingles from one side over the valley flashing, forming a neat edge while preventing water from seeping under the shingles. Open metal valleys are lined with a metal flashing that’s visible, offering a durable water channel. The main reasons valleys need attention are that they concentrate water flow, making them vulnerable to leaks if not properly sealed and flashed. Over time, harsh weather or poor installation can cause warping or gaps, which you might notice through water stains inside the house or shingle discoloration along the valley lines.
Homeowners can perform safe DIY checks by looking closely at valley areas for cracked, missing, or curling shingles and inspecting the flashing if visible. It’s also wise to check for debris accumulation which can trap moisture and cause deterioration. While gravel or granule loss is normal, excessive damage should be a red flag. If you’re unsure, a quick water test with a garden hose during a dry day can help reveal leak points. However, because valleys are prone to subtle problems that worsen over time, calling a professional roofer at the first sign of wear is important. When hiring a contractor, ask if they use a specific type of valley detail suited to your roof’s pitch and environment and whether their work will maintain your shingle warranty. Also, inquire about the flashing materials and how they ensure a watertight seal without compromising the shingles. This approach keeps your roof strong and leak-free for years.