What type of valley uses interwoven strip shingles for protection against seepage without the need for metal flashing?

The correct choice is the closed valley. This type of valley utilizes interwoven strip shingles, which are laid in such a way that they overlap and interlace with the shingles on either side of the valley. This method of installation creates a seamless barrier against water seepage without requiring metal flashing.

The closed valley design is beneficial for certain roofing materials, as it promotes a more cohesive look, blending the shingles smoothly into the valley area. It is particularly effective when using materials like asphalt shingles, which can be shaped and interlocked effectively, providing a waterproof seal that helps manage water runoff.

In contrast, the open valley method typically employs metal flashing and showcases the valley in a more visible manner, while the woven valley integrates shingles from both sides in a pattern that resembles weaving but does not always provide the same level of direct overlap as a closed valley. The boxed valley, on the other hand, is typically used in more complex roofing designs and might involve different materials or techniques. Therefore, the closed valley is specifically designed for the interlocking shingle technique that allows for effective waterproofing without metal components.