• Alas & Bravo

Why do roof valleys leak?


Leaks can develop at valley areas due to debris buildup in the roof valleys of the home. The debris traps moisture and water, prematurely rotting the underlayment underneath. Routine maintenance to clear these critical areas of the roof can prevent leaks from developing.


The wind blows leaves and dust from surrounding areas onto the roof, where materials become trapped in places designed to direct water off it. Roof valleys are one such area. Whether they are open or closed valleys, the areas should be clear from debris.


Your surrounding landscape also impacts the frequency at which debris accumulates.


For this project, the home had closed valleys where debris had accumulated along the valley metal and between the tiles and underlayment in the area.


You can see from some of the removed tiles how dirt, blown onto the roof by the wind, had accumulated in piles perpendicular to the valley. These clumps of dirt are formed by the flow of water pushing debris underneath the tiles and to the sides,

Removing more of the area shows how this pattern continued all along the valley. Closer inspection of the debris demonstrates how it traps moisture on the roof.


Once the debris was cleared from the area, you can see in the photos above, how moisture and water had stained the underlayment below.


Any water is prevented from flowing off or drying out due to the buildup in the area. The trapped moisture and water causes the underlayment to deteriorate at a faster rate and develop into a leak. If left untreated the wood sheathing underneath can also rot due to water penetrating all layers of the roofing system.


Once the valley area is cleared from debris, the underlayment is replaced and the valley metal is installed. I cut the tiles along the valley of this home, two inches, before reinstalling them back along the area to create an open valley. An open valley requires less upkeep as water has more space to clear the area.


Debris buildup in valley areas of the roof are one of the most frequent causes of leaks in a roofing system. Less common factors are poor workmanship and incorrect installation of the material in the area.


A roof valley is an important part of a roofing system. It is responsible for diverting all water off the roof. Keeping it well maintained and free of debris through general maintenance helps ensure your roof lasts its intended lifespan.