BuildMeter guide · Structures & Carpentry
Roof Valley Measurement and Liner Guide
Measure individual valley lengths, account for liner width and end laps, and separate material quantity from the selected open, closed or woven valley detail.
Direct answer
What to know first
Measure each valley along the roof surface from its upper intersection to its discharge point, then apply the liner width and lap rules from the selected roofing system. Count valleys separately because cut lengths and end laps can create more waste than one combined linear total suggests.
Open Roof Valley Liner CalculatorMeasure along the sloped valley
Valley liner follows the roof surface, not the horizontal plan. Measure from the upper roof intersection to the lower discharge point along the valley centerline. For remote estimates, derive the sloped length from verified roof geometry and confirm it before ordering.
| Input | Why it matters |
|---|---|
| Valley length | Controls liner run and cut pieces |
| Required width | May require one or more strips across the valley |
| Roll length | Determines end joints |
| End lap | Adds material where pieces join |
| Valley count | Preserves separate layout loss |
Worked example
Four valleys are each 24 ft long. A 36 in. liner is supplied in 65 ft rolls, so one width strip is needed. Base length is 96 ft. With 10% cuts and handling, order about 106 ft, or two rolls. Longer valleys that exceed one roll also require the specified end lap.
Valley method comes first
Open metal valleys, closed-cut valleys and woven valleys use different shingle and flashing details. Manufacturer instructions may call for a centered self-adhering membrane or another approved liner beneath the finished valley. Quantity should follow the selected system.
Common mistakes
- Using horizontal plan length instead of sloped length.
- Combining all valleys without considering cut lengths.
- Ignoring required liner width.
- Nailing or lapping contrary to the roofing instructions.
- Working on a roof without fall protection and suitable conditions.
Use the calculators
Use the Roof Valley Liner Calculator for rolls, the Roof Valley Length Calculator for geometry and the Roofing Underlayment Calculator for the remaining roof deck.