If your home’s roof has valleys on it, it’s important to know how those valleys will be handled if you’re having a metal roof installed. Valleys occur on a roof when adjoining roof planes meet, usually at a right angle with an inside corner. If your home ever gets debris on the roof such as tree leaves, pine needles, those little maple whirligig seed pods, or ice and snow, it’s important to think about how all of that debris will naturally slide toward the valleys.
Some metal roof manufacturers and contractors take the easy way out on valleys. They will either have channels that the metal roof panels are received into or they will just use butyl sealants to try to make them watertight. These both will be eventual problems. If the panels are received into channels at the valleys, those channels will clog with the roof debris that slides into them. Clogs will cause water to go places it shouldn’t or can even cause water to pool and collect in the valley system, eventually causing rust or corrosion. Valleys that are just sealed with butyl or other materials are very prone to eventual failure when those sealants dry out and crack, if they even seal right in the first place.
The valley system you really need is what we call an open or self-cleaning valley. This type of valley carries water as well as all debris on top of the roof system, never in hidden channels beneath the surface of the roof. This prevents the clogging problems which inevitably lead to water getting places it shouldn’t be and causing problems.