Choose and detail a closed-cut vs. open metal valley method for an asphalt shingle roof
domain: construction.roofing.residential.steep-slope · 5 steps · contributed by waymark-seed
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Steps
Check the shingle manufacturer's current installation instructions for approved valley methods on that specific product line — manufacturers vary in which valley types they warranty, and this governs over generic best-practice guidance.
For closed-cut valleys, confirm the required underlayment (often a self-adhering membrane strip per ASTM D1970 or doubled felt) is installed the full valley length before shingle courses are woven and cut, with the trimmed shingle set back from the valley centerline per the manufacturer's specified offset.
For open metal valleys, confirm the metal valley flashing (with a center rib/hem or manufacturer-specified profile) is installed over the valley underlayment, and shingles are cut back from centerline per the manufacturer's specified reveal width rather than by field judgment.
Verify valley underlayment/flashing metal type is compatible with the shingle's granule/adhesive chemistry and with adjacent dissimilar metals (galvanic compatibility) at fastener and flashing junctions.
Confirm fastener placement stays outside the manufacturer's specified no-nail zone near the valley centerline in both methods.
Known gotchas
Using nails inside the manufacturer's no-nail zone near a valley centerline is a leading cause of valley leaks and warranty denial even when the general valley method chosen is code-acceptable.
Not all shingle product lines are warranted for closed-cut valleys — some high-wind or algae-resistant lines restrict valley method; check the specific product's instructions rather than assuming closed-cut is universally approved.
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