Closed Vs Open Valley Roof

Since it isn t bogged down by the friction shingles invariably create.

Closed vs open valley roof.

Closed valleys may have a tendency if not constructed properly to channel water under the shingles laid over the bottom layer of shingles. This allows water to fall from the higher slope to the lower slope and prevents it from going under the shingles to the roof deck. For an open valley a sheet of metal usually steel sometimes copper is fastened to the roof deck. The only type of valley that is unacceptable is the woven valley.

Although the open valley is recommended by the manufacturer closed valley is acceptable. I prefer open valleys to let the water run out on metal. Thus closed roof valleys extend the time between your roof repair projects. The metal is usually pre painted to best complement the shingles color blend.

Closed roof valleys are also more affordable as installing a metal lining costs extra. When compared to a closed valley and open valley adds an additional layer of lining. Meanwhile on an open valley roof the metal lining that prevents water from seeping into the underlayers is left exposed. Proponents of the open version say that an open flashing allows the rainwater to move away from the roof faster.

It is always a good idea to check with the manufacturer or a certified installer of the product such as ourselves. When you research this topic online you will likely find people who prefer one of these methods of the other and they will give their reason. However open valleys may be susceptible to water back up along the top of the cut off shingles in the valley if not properly trimmed potentially causing roof leaks. With closed valleys the shingle life expectancy is shortened by water wearing away the valley shingles faster than those in the field.

That said an open roof valley is a good option if you want to the metal strip to serve as an architectural detail on the roof. On a closed valley roof the shingles extend to the valley area completely closing it off.