Why Roof Valleys Create Hydraulic Bottlenecks
A normal eave collects water from one roof plane. An inside valley concentrates runoff from two intersecting roof planes into a single 3–5 foot section of gutter.
During a 3-inch-per-hour storm, a valley draining 600 square feet of roof can send more than 18 gallons of water per minute into one corner. Standard 5-inch gutters and small downspouts simply cannot process this concentrated flow.
The Three-Part Professional Fix
1. Valley Splash Diverter: An angled aluminum diverter breaks the horizontal velocity of runoff and guides it into the gutter trough instead of over the front lip.
2. Six-Inch Oversized Gutter: Gives the corner 40–50% additional hydraulic capacity and deeper freeboard for storm surges.
3. Large High-Flow Outlet: A 3x4" downspout outlet removes water faster, preventing the valley section from backing up.