How much should asphalt shingles overlap when installing flashing for a roof valley?

For the installation of flashing in a roof valley with asphalt shingles, an overlap of 6 inches is recommended. This specific measurement ensures proper water drainage and minimizes the risk of leaks, which is critical for maintaining the integrity of the roofing system. Overlapping the shingles by this amount allows for enough coverage, preventing water from seeping underneath during heavy rainfall or melting snow.

This practice is part of the standard guidelines for roofing installation, designed to enhance durability and longevity of the roofing materials. It’s essential that the flashing is installed correctly to direct water runoff effectively, as valleys can be particularly vulnerable areas where water tends to accumulate. By ensuring a 6-inch overlap, the flashing can effectively channel water away from the roof structure and minimize the potential for water damage.