Technical Bulletin

Summary

Rain screen cladding systems aim to
protect a building’s wall construction
from damages that can occur through
moisture penetration. The air cavity
design behind a cladding material
allows air to flow through the space,
which dries the insulation as well as the
back of the cladding panel.

The fiber cement product line offered
by American Fiber Cement Corporation
is installed as a rain screen system. As
the system mitigates mold and other
moisture related issues in a wall, the
fiber cement panels also benefit from
the use of a rain screen to keep them dry
and thus, preserve their look and
composition.

The panels are attached to the wall substrate
with horizontal and vertical profiles, which
hold the panel’s 3.2 lb/ft2 of dead load as
well as the wind load forces on the panel.
The vertical channels provide a desired
chimney effect, which produces air flow
along the wall cavity.

What’s the issue?

When installed properly, a fiber cement
panel in a rain screen application requires
virtually no maintenance. The high-density
panels can survive the life of the building.

To keep moisture off the back of the panels,
they must be installed with a vertical profile;
a horizontal profile cannot be attached
directly to the back of the panel. The reason
is the water that enters the system through
the open joints lingers on the horizontal
profile before the droplets can get dried up

(see Figure 1). If the panel is attached in
this configuration, the water has nowhere to
fall but into the panel. With continuous
exposure to this lingering moisture, the fiber
cement boards absorb in the water which in
turn can create problems in the appearance
of the panels. This is particularly prevalent
during construction, when the system is
completely exposed to nature’s elements,
specifically before the parapet walls are
finished and properly flashed.

Even horizontal profiles with weep holes are
problematic. The water lies between the
holes in the crevice of the horizontal profile
and the rear of the panel. The Knight Wall
System with horizontal profiles attached to
verticals is not a suitable fiber cement panel
attachment system because it does not solve
the standing water effect.

What to do

The solution is simple – always attach the back of the cladding to a vertical profile (Figure 2). This Z or
hat profile may be small but it is crucial to allow for adequate air flow to prevent moisture retention on the
panels. Attachment configurations may be solely vertical profiles or horizontal profiles with verticals
(refer to Figure 3).

This rain screen attachment system is designed to last. With proper care and up-front considerations
during installation, the fiber cement panels can be enjoyed for numerous years on the building.

For any questions, concerns, or additional information, please contact American Fiber Cement Corporation: Spencer Anderson
p: 800-688-8677 x 104
m: sanderson@afccladding.com