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EIFS Design Considerations
With any EIFS, care in detailing and workmanship are key. The following
suggestions apply to all EIFS:
- Detail all penetrations, from windows to hose bibs, to be sure that
they won’t admit water into the EIFS, or worse, into
the sheathing and wall behind.
- Provide soft joints where transitions in the substrate or joints in
the substrate may cause movement, either in plane (structural
expansion joints, floor deflection), or perpendicular to the
wall plane (differential lateral deflection of framing).
- Use two-stage joints with outer seal of low-modulus sealant, adhered
to base coat, a drained and vented joint cavity, and an inner
seal of low-modulus sealant, flexible membrane, or expanding
acrylic-impregnated foam sealant. EIFS-to-EIFS joints have
limited capacity for movement, even with low-modulus sealant.
The limit might be as little as 5 mm, depending on the modulus
of the sealant, and other parameters.1 For larger movements,
use a metal expansion joint.
- Place soft joints either at corners of openings, or well away from
them.
- Insulate outside the air barrier. Insulation inside the stud space is
roughly 50% less effective because of thermal bridging by the
framing. It may also cause condensation, corrosion, and mold
when interior moisture condenses on cold sheathing between
studs.
- Consider possible impact damage — proximity to grade, vandalism,
use of swing stages, window washing, and adjacent sidewalks,
driveways and loading docks are all factors.
- Consider potential for fading, overheating, and overcooling if dark
colours are used.
- Don’t use EIFS for window sills, tops of parapets, or other upward-facing
surfaces.
- Drain other building surfaces so they won’t discharge water
onto EIFS.
- Don’t let snow accumulate against EIFS.
- Provide drips at outer edges of downward-facing horizontal surfaces.
 These
points are highlights. Successful installations of EIFS require
knowledge, skill, and dedication. Even if you intend to rely
on other participants, consider reading the ASTM special technical
publications on the subject in addition to consulting industry
publications and representatives.
For a drained cavity EIFS using the Panels, the same features are
required as for any drainscreen or rainscreen:
- Flashing at the bottom of each cavity, to intercept water, drain it
to the exterior, and drip it free of the surface.
- A membrane barrier applied to the substrate that is waterproof,
airtight, and vapour resistant. (In some cases, with masonry
backup for instance, a designer could opt to locate some of
these functions elsewhere.)
- Vents at the flashing locations, to allow air to enter for ventilation
and pressure-moderation.
- Sheltered vents at other locations, designed to prevent entry of water,
if maximum ventilation and a drainscreen are intended.
- Closures in the cavity to separate regions of different time-averaged
exterior pressure from each other, if a rainscreen is intended.
(The cavity volume is small, compared to other cladding systems,
so closures just to limit cavity volume are not likely to be
required.)
- Cavity closures at locations other than intended vents to the exterior — at
window jambs and sills, for example.
The Stucco RainScreen Panel™ System is a new product that has
seen limited application to date. As with any new product, there
may be unanticipated problems. However, it promises to eliminate
the main weakness of EIFS “rainscreen” systems and
should see wider application in the future. To date, no EIFS
manufacturer has embraced the Panel as part of his system, but
if initial installations are successful this may change. Installations
to date have not encountered problems in construction, but have
no long term service history. Lack of encouragement from major
EIFS manufacturers has not deterred designers who see advantages
in the system.
The Panels are not just prospective components of EIFS systems. They
can also provide pressure-moderated, drained cavities in systems
with other cladding. Korax offers a simple alternative to multiple
layers of building papers with treated wood strapping for climates
where rain penetration is a problem with stucco, for instance.
Other applications are not difficult to imagine.
References
1 Williams, Mark F. & Lampo, Richard G.,“Development,
Use, and Performance of Exterior Insulation and Finish Systems
(EIFS)”, ASTM STP 1187, Philadelphia, 1995.
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