Which roofing system is less likely to employ open valleys?

Asphalt shingle roofs are less likely to utilize open valleys because they typically employ a method called closed valleys, which is more suited to their installation. In closed valley systems, the shingles overlap into the valley area, effectively channeling water away from the structure while providing a streamlined look. This approach is advantageous as it helps to prevent potential leaks and water intrusion, which are critical concerns for asphalt roofing.

On the other hand, metal roofs, tile roofs, and wood shake roofs can more commonly incorporate open valleys. In these cases, the valleys are often left uncovered by the roofing material, allowing water to flow freely into them, which is integral to their respective design and drainage systems. The materials used and the installation methods appropriate for these roofing types lend themselves better to open valley designs, allowing for more effective handling of heavy rain and snow runoff.