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Opening a Gap
It is possible to incorporate a drained and vented cavity near the
exterior face, outward from the thermal insulation, in an EIFS
system. Korax Technologies make a “Stucco Rainscreen” polystyrene
beadboard panel that has horizontal and vertical grooves in the
back to create a drained and vented cavity. The panel can be
used with conventional stucco as well as with EIFS. The panel
is attached over the primary thermal insulation, using mechanical
fasteners. Vertical channels in the panel create cavities that
lead moisture to flashings and vents at the bottom of the wall
section, and allow for ventilation. What would otherwise be vertical
ribs between the cavities are interrupted at regular intervals
by horizontal channels that slope back toward the exterior.  The
vertical channels are deep enough that any water reaching them
from the exterior will run down the surface to drain, without
reaching the primary insulation. If exterior water passes through
a rib instead, it can reach the primary insulation, but will
soon reach a horizontal groove that will lead it back to the
exterior side of the cavity. The contact area is about 40%, and
the grooves are deep enough to prevent capillary bridging. If
polystyrene is also used as the primary insulation, all of the
cavity surfaces will be hydrophobic. This increases the amount
of water that will drain from the system, as opposed to having
to be removed by evaporation and ventilation.
An EIFS with the Korax panel offers the following An EIFS with the
Korax Panel offers the following advantages over other pressure-moderated
EIFS systems:
- Type 4 or Type 3 extruded polystyrene insulation can be used for
the primary insulation. This is usually not possible with Type
PB EIFS, but the Korax panel supports the lamina.
- Thermal bridging through joints in insulation (sometimes visible on
EIFS as a contrasting absence of condensation at the insulation
joints on a cold morning) is mitigated by offsetting the joints
of the Stucco Rainscreen panels with the joints in the primary
insulation, and by the cavity.
- A peel and stick air barrier (which is not sensitive to moisture
and is uniform in thickness) can be used.
- Attachment of the EIFS does not depend only on integrity of the sheathing
or an adhesive, either of which might deteriorate due to moisture
from interior sources.
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