Page 33 - Construction Waterproofing Handbook

WATERPROOFING PRINCIPLES—THE BUILDING ENVELOPE 1.15
masonry, or stone due to freeze–thaw cycles. Watertightness also prevents rusting and
deterioration of structural or reinforcing steel encased in exterior concrete or behind
facade materials.
Waterproofing also prevents the passage of pollutants that cause steel deterioration and
concrete spalling, such as chloride ions (salts, including road salts used for deicing) into
structural components. This is especially true in horizontal exposed areas such as balcony
decks and parking garages. Prevention of acid rain contamination (sulfites mixed with
water to form sulfuric acid) and carbon acids (vehicle exhaust—carbon dioxide that forms
carbonic acid when mixed with water) is also an important consideration when choosing
proper waterproofing applications.
Building envelopes also provide energy savings and environmental control by acting as
weather barriers against wind, cold, and heat. Additionally, envelopes must be resistant to
wind loading and wind infiltration. These forces, in combination with water, can multiply
the magnitude of damage to a structure and its interior contents. Direct wind load pressure
can force water deeper into a structure through cracks or crevices where water might not
normally penetrate. It also creates vertical upward movement of water (hydrostatic pres-
sure) over windowsills and through vents and louvers. Air pressure differentials due to
wind conditions may cause water that is present to be sucked into a structure because of
the negative pressure in interior areas.
This situation occurs when outside air pressure is greater than interior air pressure. It
also occurs through a churning effect, where cool air is pulled into lower portions of a
building, replacing warmer air that rises and escapes through higher areas. To prevent this
forced water infiltration and associated energy loss, a building envelope must be resistant
and weather-tight against wind as well.
Finally, and possibly most important, health issues of building occupants are now
directly related to the success of a properly design and constructed building envelope. All
types of mold require the presence of moisture for formation and growth. This moisture is
almost always the result of leakage attributable to improperly designed and/or constructed
building envelopes. Since mold can cause numerous health problems, this may be the most
important issue necessitating a proper understanding of the building envelope and the
90%/1% and 99% principles presented throughout this book.

SUCCESSFUL ENVELOPE CONSTRUCTION

For envelopes to function as intended requires proper attention to
● Selection and design of compatible materials and systems
● Proper detailing of material junctions and terminations
● Installation and inspection of these details during construction
● Ability of composite envelope systems to function during weathering cycles
● Maintenance of the completed envelope by building owners

From the multitude of systems available to a designer, specific products that can func-
tion together and be properly transitioned must be chosen carefully. Once products are