04/12/2026
Roof Valley Installation
The image illustrates the technical procedure for installing a closed-cut valley using asphalt shingles. This method is a common architectural practice designed to channel water runoff effectively where two roof planes meet. The illustration highlights the "under-lap" phase, where shingles from the primary roof plane are woven across the valley center to create a continuous, waterproof base before the secondary plane's shingles are installed and cut back.
Key Features and Analysis
Underlayment: The dark, waterproof membrane (typically felt paper or synthetic wrap) that serves as the secondary barrier between the roof deck and the shingles.
Valley Center: The critical intersection line where two sloping roof planes meet, forming a trough for water drainage.
Shingle Overlap: The shingles from the first side are extended across the valley. The annotation specifies extending the top corner at least 12 inches beyond the valley center to ensure no water can seep under the shingles at the joint.
Fastening Pattern: The shingles are laid in a staggered, overlapping fashion to ensure that joints do not align, which prevents capillary action from pulling water upward.
V-Shaped Geometry: The architectural layout shows an inside corner (concave), requiring precise flashing and shingle weaving to maintain structural integrity.
Concept Summary
The illustration provides a clear technical guide for ensuring hydrological integrity in residential roofing. By extending the shingles 12 inches past the valley center, the installer creates a "blind" water barrier. This specific technique is preferred for its clean aesthetic and durability, as it protects the most vulnerable part of the roofβthe valleyβfrom leaks caused by ice damming or heavy rainfall.