Page 26 - Construction Waterproofing Handbook

1.8 CHAPTER ONE

FIGURE 1.7 Drainage waterproofing system.

cavity-wall dampproofing and flashing to divert penetrating water and water vapor back to
the exterior. Refer to Fig. 1.7.
A new term in construction design is being used, namely, rain-screen system. This is
simply another term for drainage system. Rain-screen systems use cavity-wall systems in
curtain-wall and similar construction techniques, where the air space in the cavity wall is
used to prevent air pressure from permitting water to enter the initial barrier facade com-
ponents into the interior portions of the building.
Diversions actually redirect water being forced against envelope components and divert
it elsewhere before it infiltrates or absorbs into the substrate. These might include sloping
of roof decks and balconies, vertical drainage mats applied to below-grade walls, gutters
and downspouts, flashings, and wind screens. Refer to Fig. 1.8 for typical examples of
diversion systems.
Building facades usually contain combinations of these systems, each preventing water
infiltration at their location on the envelope. However, regardless of how well the individ-
ual systems function, if they are not properly transitioned into other envelope components
or terminated sufficiently, leakage will occur. These situations become the major issues pre-
venting effective building envelope and waterproofing functioning and are the cause of most
leakage that occurs in all structures.

Completing the Envelope
Once the sources of water have been identified, the types of systems to prevent leakage cho-
sen, and the materials selected to provide necessary aesthetics to the finished product, the
envelope design must be carefully constructed and reviewed to ensure successful perfor-
mance of the completed product. To prevent all possible water intrusion causes, a building