Valleys are created when two sloping roof areas intersect and
are one of the critical detail points on a steep-slope roof system.
They occur on primary roof areas and where projections, such as
dormers, break the plane of the main roof. A valley's main function
is to create runoff pathways to direct water flow from the roof
planes into a valley trough. The volume of water varies with the
valley's length and slope.
Because of their configurations, valleys are susceptible to
debris accumulation from vegetation, foliage and windborne
particulates. Valley function and service life are affected by
climatic conditions such as snow, ice, rainfall frequency and
intensity, humidity, temperature extremes and wind. Geographic
factors influencing valley function and service life include
building location, elevation and oriented exposure to solar load
All these issues determine which valley configuration is
appropriate for the specific building and selected roof system; I
will discuss valley configuration as it relates to asphalt
The three basic valley types for asphalt shingle roof systems
are woven, open and closed-cut. In addition, there are recognized
options for open and closed-cut valleys commonly referred to as
"California open valleys" and "California...
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