Page 25 - Construction Waterproofing Handbook

WATERPROOFING PRINCIPLES—THE BUILDING ENVELOPE 1.7
effective systems to prevent such intrusion. Expected conditions for a particular geo-
graphic area that will affect the above-grade envelope are available from the national
weather service at www.nws. noaa.gov. Below-grade water tables are determined by testing
actual site conditions.
It also should be understood that substrate water penetration and absorption do not nec-
essarily cause leakage to interior spaces. Water absorption occurs regularly in masonry
facades, but the masonry is either large enough to absorb the penetrating water without
passing it on to interior finishes or this water is collected and redirected back to the exteri-
or by the use of dampproofing systems. Water penetration also occurs at the microscopic
and larger voids in the masonry mortar joints, but again, the masonry absorbs it or the water
is redirected back out through the dampproofing system.
For definition purposes, water infiltration and leakage are used interchangeably in this
book because each is not an expected outcome in envelope design. All envelope compo-
nents are designed to prevent leakage or infiltration by one of three systems:

1. Barrier
2. Drainage
3. Diversions

Barrier systems are, as their name implies, effective and complete barriers to water
infiltration. They include actual waterproofing systems such as below-grade urethane
membranes and other envelope components such as glass. They completely repel water
under all expected conditions, including gravity and hydrostatic pressure. Refer to Fig. 1.6.
Drainage systems are envelope components that might permit water absorption and
some infiltration through the substrate but provide a means to collect this water and divert
it back out to the exterior before it causes leakage. Examples include masonry walls with

FIGURE 1.6 Barrier waterproofing system.