Valley metal comes in 10-foot lengths that overlap 6 inches, so each piece covers about 9.5 feet of valley. Measure along the valley line itself, not the horizontal distance — it runs diagonally across two slopes and is always longer than it looks from the ground.
The Valleys Calculator returns the linear feet of valley material — ice & water shield, W-metal, or closed-cut valley shingles — needed for every valley on your roof. Enter the total linear feet of all valleys and select an installation type and the tool returns roll count or piece count with proper overlap. Valleys carry the most water of any part of a roof, so accuracy here is critical. Pair with our Flashing and Underlayment calculators for full waterproofing coverage.
Valley material is measured along the valley line, which is longer than it looks from the ground because it runs diagonally across two slopes. Valley metal comes in 10 foot lengths and overlaps 6 inches at each joint.
| Valley length | 10 ft pieces (6 in lap) | Ice barrier at 36 in wide |
|---|---|---|
| 12 ft | 2 | 0.2 rolls |
| 20 ft | 3 | 0.3 rolls |
| 32 ft | 4 | 0.5 rolls |
| 48 ft | 6 | 0.7 rolls |
| 64 ft | 7 | 1 rolls |
Open valleys show the metal and shed debris well. Closed-cut valleys hide it and look tidier but hold pine needles and grit, which is what eventually causes the leak.
An open valley leaves the metal exposed down the centre with the shingles cut back on both sides. It sheds water and debris fastest and it is the easiest to inspect, which is why it is the most reliable of the three. A closed-cut valley runs one plane’s shingles through and cuts the other plane back over them; it looks tidier and costs less in metal but traps grit and pine needles. A woven valley alternates courses from both planes; it is rarely used with architectural shingles because they are too thick to lie flat through the weave.
Whichever detail you choose, measure the valley length on the slope. A valley across two 6/12 planes is noticeably longer than the plan view suggests, and ordering off the plan length comes up short.
Measure along the valley line itself, from the eave to where it meets the ridge. It runs diagonally so it is always longer than the horizontal distance suggests.
Open valleys expose the metal and shed debris and water fastest, which makes them the more reliable choice. Closed-cut valleys look neater but trap pine needles and grit that eventually cause leaks.
Yes, in any climate with freezing weather. Valleys concentrate both water and ice, and self-adhering ice barrier the full length of the valley is standard practice.
Typically 20 to 24 inches wide overall for a residential open valley, giving roughly 3 to 4 inches of exposed metal down the centre with the rest under the shingles. Wider valleys are used where two large planes drain into one, because the volume of water is higher.