Page 20 - Construction Waterproofing Handbook

1.2 CHAPTER ONE
THE BUILDING ENVELOPE

The building envelope is equivalent to the skin of a building. In essence, a structure must
be enveloped from top to bottom to prevent intrusion from nature’s elements into interior
spaces and to protect the structural components from weathering and deterioration.
Envelopes complete numerous functions in a building’s life cycle, including

● Preventing water infiltration
● Controlling water vapor transmission
● Controlling heat and air flow, into and out of interior spaces
● Providing a shield against ultraviolet rays and excessive sunlight
● Limiting noise infiltration
● Providing structural integrity for the façade components
● Providing necessary aesthetics
● Preventing of mold formation and growth
While the main purpose of any building envelope is to provide protection from all ele-
ments, including wind, cold, heat, and rain, this book concentrates on the controlling of
water and leakage for all construction activities including the building envelope. Making a
building envelope waterproof also provides protection against vapor transmission and
serves to prevent the unnecessary passage of wind and air into or out of a building, assist-
ing in the controlling of heating and cooling requirements. Before considering each specific
type of waterproofing system (e.g., below-grade), some basic concepts of waterproofing
and how they affect the performance of a building envelope are important to understand.

INTRODUCTION TO WATERPROOFING AND ENVELOPE DESIGN

Waterproofing is the combination of materials or systems that prevents water intrusion into
structural elements of a building or its finished spaces. Basic waterproofing and envelope
design incorporates three steps to ensure a watertight and environmentally sound interior:

1. Understanding water sources likely to be encountered.
2. Designing systems to prevent leakage from these sources.
3. Finalizing the design by properly detailing each individual envelope component into
adjacent components.

Water Sources
Water likely to penetrate building envelopes is most commonly from rainwater on above-
grade components and groundwater intrusion below-grade. Other sources also should be
considered as appropriate, such as melting snow, overspray from cooling towers, land-
scaping sprinklers, and redirected water from such sources as downspouts and gutters.
The presence of any of these water sources alone, though, will not cause leakage; for leak-
age to occur, three conditions must be present. First, water in any of its forms must be present.