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Roofingaka: roof valleyaka: valley flashing

Valley

In Plain English

The V-shaped channel formed where two roof slopes meet — one of the most water-vulnerable areas of any roof.

Definition

The internal angle formed where two sloping roof surfaces meet, creating a channel that concentrates and directs rainwater down the roof. Valleys are among the most leak-prone areas of a roof and require special waterproofing — either open metal flashing or a closed/woven shingle detail. Ice and water shield is typically required in the valley for cold climate applications.

Why It Matters in Bidding

Valleys concentrate the most water on any roof, so in bidding they drive both material selection and labor productivity in the takeoff. Estimators must measure valley linear footage separately because it carries added cost for metal flashing or woven detailing, ice-and-water shield, and slower install rates. Underestimating valley work or omitting the underlayment is a common source of callback claims and warranty exposure.

Example

Doing a reroof takeoff, the estimator measures 86 linear feet of valley and prices open metal valleys with a full-width ice-and-water shield underlayment, flagging it as a separate line so the homeowner sees the leak-prone detail is upgraded.

Related Terms

FlashingRidgeShingleCricket

Frequently Asked Questions

Valleys require added materials such as valley metal or extra shingles for weaving, plus ice-and-water shield, and they install slower than field areas. Pricing them at the standard square-foot rate understates cost. Breaking out valley linear footage lets the estimator apply the correct material and labor unit rates and avoid eroding margin.
Open metal valleys add the cost of pre-finished flashing material and more labor to set and seal it, but install faster than weaving. Closed or woven valleys use no extra metal but consume more shingles and skilled labor. Estimators price the specified detail; substituting one for the other without an addendum risks a nonresponsive bid.
In cold climates most codes and manufacturer warranties require a self-adhering ice-and-water membrane in valleys to resist ice damming and wind-driven rain. Estimators should confirm the code requirement and the manufacturer's warranty conditions, since omitting it can void the system warranty and create liability the bid never accounted for.

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