General

The objective of designing an effective weather-resistant building envelope is simple: keep rainwater away from vulnerable construction materials. Keeping these components dry will maintain a building’s structural integrity and help prevent moisture-related problems as mentioned in Section 4.1.

Rainwater is widely acknowledged as the most problematic external source of moisture for buildings.9, 10, 11, 12 Sections 4.2.2 through 4.2.9 provide actionable guidance for designing durable, moisture-resistant roofs and exterior walls; refer to Chapter 3 for similar guidance on foundations and site design. Other forms of precipitation that cause water intrusion also are not neglected. For example, snow is considered in relation to its role in the formation of roof eave ice-dams. In Section 4.4, additional resources are provided for further study and guidance.