SYSTEMS/MASONRY
Figure 4.2.10 shows air leakage at the interface of steel columns and concrete block. The
exfiltrating interior eventually condensed on the cold metal siding, resulting in severe crumbling of
the block at the outer wythe. This case points out the need to provide an appropriate air barrier at
the intersection between steel columns and masonry. The air barrier element must be able to
compensate for construction tolerances, differential movement of the block wall and the structural
elements, and block shrinkage. The intersection between masonry walls and other envelope
elements is a key area for achieving air barrier continuity.
UNACCEPTABLE
Outside
Metal
Figure 4.2.10 Air Leakage at Block / Column Joint
(Quirouette 1983)
Figure 4.2.11 shows an example of an air barrier discontinuity at a window/wall interface
(Quirouette 1983). In this case the wall air barrier and the window air seal are not in line with one
another, resulting in a major discontinuity in the air barrier. Similarly, the wall insulation is out of line
with the window thermal break. Quirouette points out that this design has been found to result in
condensation on the inside mullion surface and efflorescence on the outside surface of the brick
veneer.
As in the case of thermal insulation, the air barrier in a cavity wall can be placed either inside or
outside of the backup wall and the insulation. The advantages of an inner air barrier include
accessibility during construction and the associated ease of inspection and repair. In addition, if the
air barrier and associated seals are positioned inside of the insulation then they are protected from
outdoor temperature fluctuations, reducing the differential movement to which they are subjected
and easing the material requirements on the sealants. The disadvantages of an interior air barrier
involve the detailing required to seal the wall air barrier around columns, floor slabs and other
structural members. The advantages of positioning the air barrier outside of the backup wall
include having a continuous surface over which to apply the air barrier without having to work
around interruptions from structural members. Whether the air barrier is inside or outside the
insulation will determine the temperature environment to which it is subjected, affecting the material
requirements for the air barrier.
PAGE 4.2-14
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