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EIFS manufacturers have made signiﬁcant strides in successfully remedying the
entrapped moisture problem by adding a drainage plane.
Voids created through vertical adhesive patterns and/or strips of manufactured
drainage material maintain effective drainage, without overly decreasing R-value.
Many are specifying rigid board stock insulation to be applied outside the wall
sheathing, but this may create a system remarkably similar to early EIFS—and
without the beneﬁt of the drainage plane.
EIFS and entrapped moisture
There are additional scenarios that have caused
a great deal of problems. For example, issues
occur when board stock rigid insulation is layered
against other rigid insulation or exterior sheathing,
or when decking traps moisture between the layers
of material. This phenomenon ﬁrst happened on a
wide scale in early exterior insulation and ﬁnish
systems (EIFS). Moisture entered these systems
and became entrapped behind the rigid insulation
and in front of the wall sheathing on the backup
wall, deteriorating the water-resistant barrier
(WRB), sheathing, and structural studs (Figure 3,
Moisture entering these early EIFS assemblies
(through any of the methods previously mentioned
became held for an extended period in the pockets/
voids in the exterior building envelope created by
the variations between the rigid insulation surface
and the wall sheathing surface. This negative
scenario was ampliﬁed by the composition of
the two layers of materials involved.
The EIFS industry started addressing this
problem by incorporating a 3.175-mm ( 1 / 8 -in.)
drainage plane between the back side of the
board stock rigid insulation and the exterior
face of the sheathing or the WRB installed over
the sheathing. Created through vertical adhesive
patterns and/or strips of manufactured drainage
material (Figure 4), this void became the
accepted solution because it caused the least
decrease in R-value while maintaining effective
drainage characteristics. It also allowed
accumulating moisture to effectively drain
down and out the wall.
Additionally, this size was chosen because
anything smaller could have allowed capillary
action. When a wet layer is in close proximity
to a dry one (i.e. less than 3.2 mm [ 1 / 8 in.] of
separation), moisture moves between them.
As the Whole Building Design Guide states:
Once wetted, capillary transfer within, or between,
layers of an exterior wall assembly can also occur,
and can be further exacerbated by moisture loads
inherent to an exterior wall product or material
shortly after initial installation. 2
These voids are not widely promoted features
of EIFS because the cladding systems qualify,
72 the construction speciﬁer | september 2013
8/14/13 8:59:26 AM