Page 431 - Construction Waterproofing Handbook

THE BUILDING ENVELOPE: PUTTING IT ALL TOGETHER 10.33

FIGURE 10.34 Transition from vertical envelope areas to roof or horizontal areas. (Courtesy of Emseal)

Parapet walls create a particular problem in the life-cycling of a structure. Many unique
stresses occur at parapet walls due to the imposed designed loads. Parapet walls move both
vertically and horizontally due to thermal movement. In addition, both sides of parapet
walls are exposed to weathering, which exemplifies this movement of horizontal and ver-
tical expansion and contraction.
Introduction of an adjacent roof slab, which expands against or contracts away from a
parapet, imposes a great amount of additional stress on a parapet wall. These stresses may
cause bowing of parapet walls and cracking of facing materials or systems that lead to
water intrusion. Once begun, this entering water imposes additional stresses such as
swelling, freeze–thaw cycling, and corrosion of reinforcement. Often, parapets eventually
fail to function properly.
When unbreathable coatings are applied to a roof side of parapets, such as black
asphalts, heat absorption into parapets increases. This type of waterproofing can damage
the integrity of a parapet structure. The numerous situations involved with parapet con-
struction require special designs to ensure that sufficient structural components as well as
control and expansion joints are included in construction.