Final answer:
For asphalt shingle valleys, a 12-inch overlap is recommended for closed-cut or woven installations, ensuring a secure and water-tight valley. Older methods had less overlap, but modern standards have increased the overlap requirements for better protection.
Step-by-step explanation:
When installing asphalt shingle valleys, there are specific requirements for the overlap to ensure a water-tight seal. Although older practices suggested minimal overlap, current standards recommend more generous overlapping to prevent leaks. For a closed cut or woven valley, which is a technique where shingles from both sides of the valley extend across the valley and are interwoven or cut to fit, the typical recommended overlap is 12 inches. This allows for adequate coverage and a strong bond between the layers.
On the contrary, an open valley configuration, where the valley is lined with metal or another material and shingles do not overlap, would typically require at least a 6-inch overlap of the shingles onto the valley lining. However, for the best practice and to choose any one option in the final part clearly, mention the correct option in the final answer, which is a 12" closed cut or woven. This guideline follows the most updated roofing techniques and provides enhanced protection against water infiltration.