Fiberglass shingles are a popular roofing material favored for their durability and affordability, but like any roofing system, they can develop leaks, especially in the valleys where two roof slopes meet. Valley leaks under fiberglass shingles often occur because these areas experience heavy water flow during rain, which can expose weaknesses in the installation or materials. Common causes include improper underlayment, damaged or missing shingles, and poor sealing around flashing or ridge caps. Sometimes, valleys that don’t have proper metal flashing or have old, worn-out flashing can allow water to seep underneath the shingles. Diagnosing such leaks from inside your attic might reveal dark stains, mold, or dampness. Outside, you might see missing granules on shingles, cracked or curled shingles, or visible rust or damage on the metal flashing. Safe DIY checks include clearing debris from valleys, inspecting for damaged shingles, and checking for obvious signs of flashing issues. Avoid walking on the roof unless you are confident and safe, and never attempt to remove or replace flashing without proper knowledge.
When leaks are suspected in valley areas, calling a professional roofer is often the best course of action to avoid accidental damage or voiding your roof warranty. A qualified roofer will inspect the valley’s underlayment, flashing, and shingles and can suggest suitable repairs such as replacing flashing with durable metal pieces or installing specialized valley liners. When consulting a contractor, ask directly if they use metal flashing in valleys rather than relying on shingles alone and whether their repair work will maintain or improve your roof’s warranty status. You might also want to inquire about their approach to valley waterproofing—do they use woven valleys or closed-cut valleys, and what materials do they recommend for your specific roof and climate? Proper valley repair is critical because it impacts the overall integrity of your roof’s water-shedding ability, so ensuring your roofer understands these nuances is essential.