ENVELOPE SYSTEMS/EIFS
4.7 EXTERIOR INSULATION FINISH SYSTEMS (EIFS)
EIFS envelope systems offer the advantages of cost effective construction and exterior insulation of
building structural elements, eliminating the associated thermal bridges. Figure 4.7.1 shows the
basic components of an EIFS wall, in this case employing a metal stud wall substrate. The unique
aspect of this system is the cementitious or stucco finish that is continuously applied to insulation
boards that are attached to a substrate. An article by Labs discusses the basic components of
EIFS and some recent developments. The Exterior Insulation Manufacturers Association (EIMA)
has produced a series of guideline specifications for EIFS, which are primarily directives to follow
the instructions of product manufacturers. EIFS are classified by EIMA as polymer based (Class
PB) or polymer modified (Class PM). PB systems are also referred to as thin coat, soft coat or
flexible systems, while PM systems are sometimes referred to as thick or hard coat.
Figure 4.7.1 Components of EIFS Construction
EIFS employ the face-seal approach to leakage control in which the exterior face of the envelope is
sealed to prevent both air leakage and rain penetration. As with all envelope systems, moisture
tightness is very important for EIFS to prevent the degradation of system components and to
protect the wall's integrity. Water may enter the system at leaks in panel joints, at locations where
delamination has occurred, and at voids in the finish coat when exposed to moisture for extended
periods of time. The latter problem can occur at joints that do not drain well or at other facade
articulations. It is important to design roof edges, window sills and other articulations to shed water
away from the building, rather than continuously testing the water-tightness of the building skin. The
control of water vapor diffusion requires a vapor retarder, specifically designed for the climate and
the wall insulation level. In cold climates, this vapor retarder must be placed inside of the insulation
and must have a water vapor permeance sufficiently below that of the exterior finish. In hot
climates the exterior finish could serve as the vapor retarder, providing it has a sufficiently low
permeance. However, it is crucial that the face sealing is continuous and durable to prevent hot,
humid air from migrating into the envelope and condensing on cold elements. It is also important in
hot climates that extreme care be exercised if a highly vapor impermeable interior finish (e.g. vinyl
wallcovering) is used, as it may be less permeable than the outer face, resulting in condensation
behind the interior finish. If such an interior finish is employed or anticipated, another vapor retarder
may be needed within the envelope. This additional vapor retarder should be installed outside of an
additional layer of insulation.
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