Open valley vs closed valley: which is better?
Short answer. Neither is better everywhere: open metal valleys move heavy water and debris best and suit roofs under pines and big trees, while closed-cut valleys look cleaner, cost a little less, and perform very well when installed over self-adhering membrane with correct nailing and trimming. In Georgia, open valleys earn their keep on long, heavily treed valleys, and closed-cut valleys are the common, reliable choice on most homes.
Open valley
- How it works: a strip of metal, often with a center crimp, runs down the valley, and shingles on each side are cut back so the metal stays exposed.
- Strengths: high water capacity, debris slides down instead of lodging in shingle edges, and the metal outlasts valley shingles.
- Drawbacks: visible metal, extra material and labor cost, and metal that hail can dent.
- Code: metal linings for open valleys must be at least 24 inches wide.
Closed-cut valley
- How it works: shingles from one slope run through the valley; shingles from the other slope lap over them and are cut 2 inches back from the centerline, with corners clipped.
- Strengths: a clean, all-shingle look, lower cost, and approval from shingle makers for laminated architectural shingles.
- Drawbacks: water runs over shingle surfaces, so valley shingles wear faster; poor nailing or cutting shows up as leaks; debris can catch on the cut edge.
- Lining: self-adhering membrane underneath is standard practice.
Woven valleys
Shingles interlaced across the valley are common on old 3-tab roofs, but GAF does not allow them with its laminated Timberline shingles, which crack when woven.
How to choose
- Lots of pine needles and leaves, long valleys, or two big slopes feeding one valley: open metal.
- Short valleys, little tree cover, or an HOA that prefers an all-shingle look: closed-cut.
- Either way: membrane underneath, no nails near the center, and valleys kept clear.
See ice and water shield in Georgia and pine needles and leaves on the roof.