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2.2.2 Roof Flashing

Water penetration is commonly associated with flashing and detailing problems around roof penetrations, eaves, and wall intersections with a lower roof section. The following best practices describe flashing details for common applications in residential construction that inspectors should be able to recognize. These conceptual details are intended to help the inspector understand the objective for roof flashing, as found in the 2006 IRC:

R903.2 Flashing. Flashings shall be installed in such a manner so as to prevent moisture from entering the wall and roof through joints in copings, through moisture-permeable materials, and at intersections with parapet walls and other penetrations through the roof plane.

U.S. building codes provide only basic performance concepts for use and detailing of flashing. Therefore, it is imperative that designers and builders consider the issue of roof flashing as a key element of construction plan detailing, construction trade coordination, and field quality-control. Oftentimes, inspectors discover flashing details incorrectly installed, or even flashing that is missing. Manufacturers’ recommendations and the industry’s standard installation guidelines provide a valuable resource for inspectors to understand flashing details.

Flashing Details for Roofs

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Figures 4 through 7 provide models for correct flashing installation techniques for asphalt composition shingle roofing, which is the most common roofing material used in residential construction in the U.S. For flashing details for other roofing types, the inspector should refer to the manufacturer’s literature and industry guidelines.

To avoid roof leaks, appropriate flashing details should be installed wherever possible; roofing cement and caulk should not be solely relied upon for adequate sealing purposes. In addition, improper or missing kick-out flashing (which may involve only a single roof flashing component) is associated with some of the more severe cases of localized moisture damage to walls. This flashing element is highlighted in Figure 7. It is commonly referred to as a kick-out (or kickout) flashing or an end-dam flashing.

To ensure that the ice-dam flashing at the eaves extends 24 inches horizontally beyond the exterior wall, the slope of the roof should be accounted for.

Table 2 offers nominal width requirements for the ice-dam flashing at the eaves based on different roof slopes and the eaves’ overhangs. Note that for many scenarios, a single 36-inch roll of flashing may not be sufficient.

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