Roof valleys must be carefully designed so that water does not seep past the flashing edges nor stream beneath the shingles. While simple roofing styles have no valleys, complex systems with multiple slopes form internal angles that invite leakage. Rain gushes down the slopes of the adjoining roof planes and accumulates along the narrow depression. If all the roofing components have been sealed properly, then the water gently makes its way to the edge and causes no problems. However, a small crack or puncture can allow moisture to enter the attic area and walls, creating the potential for damage. Sugar Land roofing professionals can help property owners identify areas of concern and prevent the need for repair.
When roofers intersect slopes, they construct either open or closed valleys. Both types have advantages and disadvantages. The best choice is a matter of personal preference. In an open system, shingles are laid along the slopes but are cut off before crossing the valley. This technique leaves the metal valley flashing exposed. On the contrary, a closed valley consists of shingles all the way across so that the underlayment is completely covered.
The roofing contractors from Houston Restoration Services of Sugar Land TX can answer any questions about commercial roofing or storm damage.
Variations in pattern such as woven and cut arrangements exist for closed systems, but the shingles act as the lining for water resistance in each style.
The metal lining in an open valley should extend on both sides at least eight inches. Likewise, the adjacent shingles can function adequately if they overlap the flashing by four inches or more. The shingles that are cut off must be installed properly in order to prevent the occurrence of cross wash. Since the flashing is the primary moisture barrier along an open valley, the metal should be a minimum of 18 inches wide with a splash diverter. A thick, corrosion resistant metal that does not stain is necessary.
Woven valleys are less common than cut designs, but they still cover the whole area by extending shingles across to the adjacent slope. This type of closed valley is functional for roofing systems with a pitch of 4:12 or higher. Since shingles from both sides are laid across the valley in an alternating pattern, the roofer must be sure that the system forms a watertight covering.
Closed systems require the shingles to be somewhat bendable as they are laid along the valley. When heavy shingles are used, they often crack more readily than their thin counterparts. A basic asphalt shingle with a fiberglass mat may serve the purpose better than a thick laminated product.
