Civil Engineering Reference
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are anchored to a retaining track fastened into the slab.
•
The head of the window-wall system is slotted into a deflection
header fastened to the underside of the floor slab, spandrel beam,
or structural wall and anchored to the structure with deflection
straps.
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Horizontal mullions dividing the window-wall unit into panels of
vision glass units, glazed from either the exterior or interior, and
glass or metal opaque panels mounted from the exterior.
•
Operable units, typically awning or casement windows, swing
doors, and sliding doors, mounted within the frame of the win-
dow-wall system.
•
A slab band cover spanning the depth of the slab that can be in-
stalled either independent of the window-wall system or as an ex-
tension of the window-wall frame.
Early window-wall systems typically used a face sealed approach
to their design with respect to water tightness, relying on the continu-
ity of the primary exterior seal to prevent water infiltration. Many of
these systems have experienced chronic water infiltration problems as
the result of deficiencies in the primary exterior seal. These were often
aggravated by air leakage that emphasized the deficiencies in the pri-
mary exterior seal under differential pressure. Once the water is past
the exterior seal, it often accumulated within the frame, as there was no
provision to contain this water or to drain the interstitial cavities. Even-
tually, the accumulating water overflowed to the interior.
These frequent water ingress problems have led to the adoption
in recent years of rain-screen design concepts. The adaptation of rain-
screen concepts to window-wall systems was twofold. In the first in-
stance, a second line of protection against water penetration was pro-
vided inboard of the original primary exterior seal. Different assemblies
within a typical window-wall system require different approaches to
providing an effective second line of protection, including
•
Installation of a secondary seal for the vision units, typically pro-
vided by a heel bead of sealant applied between the inside light of
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