SYSTEMS/MASONRY
When insulation is placed in the cavity, a secure means of attachment is critical. The insulation
within the cavity is subjected to outside wind pressures, and if it becomes displaced, it can interfere
with the drainage of water from the cavity and lose its effectiveness as an insulator. In addition,
there must not be any air gaps behind the insulation, otherwise air will then be able to flow around
the insulation, severely degrading its effectiveness. Rigid insulation boards are often used as cavity
insulation, and in order to be effective, these boards must be fixed tightly to the outside surface of
the backup wall. Depending on the condition of the backup wall surface, it may be necessary to
parge the backup wall to provide a flat surface for application of the insulation. Rigid insulation can
be attached to the backup wall with adhesives, mechanical fasteners or a combination of both.
When using adhesives it is important that the surface of the backup wall is clean and smooth. The
back of the board must be fully buttered with adhesive, since spot adhering will result in air gaps
behind the board. Weather conditions may restrict the use of some adhesives. One must also
address their compatibility with the insulation and their long term stability and effectiveness with
regards to aging, attack from biological organisms, and temperature and humidity cycling.
Mechanical attachment using the brick ties or screw and washer assemblies has advantages over
adhesives since they can be used under any weather conditions. Rigid, fibrous insulation is
sufficiently flexible that mechanical anchors will pull the insulation into close contact with the backup
wall.
When cavity insulation is used, the cavity must be wide enough to allow for the cleaning of any
mortar droppings from the cavity. One can use insulations specifically designed to fill the cavity and
allow for drainage, such as semi-rigid glass fiber boards. Such an approach also has the
advantages of preventing mortar droppings since the insulation is in place when the veneer is
installed.
In the case of rigid insulation boards, achieving secure attachment requires a solid surface for
affixing the insulation and a means of attachment that can withstand the environment to which it will
be subjected. Figure 4.2.7 shows an insulation adhesion failure caused when the brick ties
prevented the insulation from achieving full contact with the backup wall. As a result, very little of
the asphalt adhesive on the back on the rigid insulation actually contacted the block. Air moving
through the block wall, due to the lack of an air barrier system, was free to move through the
spaces on both sides of the insulation. In this case, severe condensation resulted on the outer
surface of the backup wall. This problem could have been avoided through the use of an air barrier
system and an alternative means of attaching the insulation.
UNACCEPTABLE
Figure 4.2.7 Insulation Attachment Failure
PAGE 4.2-11
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