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Drift Joints Provide an Avenue for Water Intrusion Into Wall Cavities

May 15, 2011

Any “break” in the continuity of a weatherexposed,
three-coat cement plaster exterior
wall system increases the opportunity for
uncontrolled moisture to penetrate the exterior
plane and enter through the cladding.
“Uncontrolled rainwater penetration and
moisture ingress remain two of the most common threats
to the structural integrity and performance of the building
Commonly referred to as “accessories,” these components
serve multiple purposes: as design elements to add
visual enhancements to the surface (such as reveals), as
a place for minor cement plaster movement such as crack
control joints, or as a component for structural movement
in order to minimize the damage that could affect the
This article focuses on the use (or misuse) of the common
#40 horizontal two-piece drift/seismic joints (see
Illustration 1) in stucco, the significant concern with water
that is captured by the joint’s lower pocket, and subsequent
leakage at the ends and joints of each piece.
Further, the need for the horizontal upper metal accessory
to provide weepage is discussed.
Illustration 1 —
A vendor’s
illustration of a
drift joint (from
Dietrich Metal
Photo 1 – Note the exposed termination of the lower pocket of the #40 drift
joint against the window jamb metal flange. It is unsealed and will drain
water that is trapped in the lower pocket into and down the jamb WRB.
Water was leaking into the building at the window perimeters during
significant rain and leaked from spray testing.
28 • I N T E R FA C E MA R C H 2011
MA R C H 2011 I N T E R FA C E • 2 9
The most common three-coat stucco
cladding system can be described as an
“internal drainage plane wall” system. As
such, three-coat stucco is designed as a
first line of defense to deflect most, if not all,
of the moisture that contacts the surface to
the outside – the first line of defense.
Behind the stucco system is a “weatherresistant
barrier,” generally a codeapproved
building paper, intended to manage
small amounts of incidental moisture
that may have penetrated past the stucco
system, allowing it to drain out at exit
points (screeds and other flashings) or
absorb the moisture, then dry back out
through the plaster surface or inward,
depending on permeability.
Codes require a minimum of two layers
of Grade D (60-minute) paper or approved
equivalent over solid sheathing, and a single
layer over open framing. Grade D is a
water-vapor-permeable paper. Grade D
paper with a water resistance of 60 minutes
(or more) is intended for stucco applications
and is often preferred to Grade D paper that
has only the minimum 10-minute resistance
required by UU-B-790a. When the
paper is subjected to excessive, uncontrolled
amounts of moisture, water can seep
past laps and penetrate through fasteners.
In addition, excessive wetting of the paper
will overwhelm its ability to shed moisture,
leading to saturation and transfer of moisture
through the paper, eventually into the
wall and cavity.
Horizontal, two-piece-type expansion
joints, such as
the accessory
#40 joint, available
in 10-ft
lengths, have a
design. The fe –
male part,
which has a
receiver groove
or pocket, is
placed at the
lower configuration.
This layout,
very common in the field, will intercept and
collect large amounts of water running
down the stucco into the groove, where it
travels horizontally to the ends of each piece
and either joins the next piece or terminates
at corners, edges, and jambs. Excessive
amounts of moisture tend to leak out at
these locations and enter into the wall system.
Also, stucco that terminates at the bottom
of the upper accessories that does not
allow drainage causes moisture to accumulate,
back up, and travel horizontally
uncontrolled. The subsequent moisture
intrusion can then overwhelm the weatherresistant
barrier by excessive wetting and
through-fastener holes and other voids.
Review the Need for the Accessory
Drift/Seismic Joints
A careful analysis of the structural
design (governed by the requirements of the
seismic sections of the most current building
codes) should be performed to determine
the necessity and possible elimination
of the horizontal cladding drift joints.
In the case of shear walls, for example,
the floor–to-floor drift or deformation
should be negligible and elements
attached to the wall should
be subject only to acceleration
forces. Commonly used methods of
the attachment of additional facing
materials to the building structure,
if correctly designed and installed,
should ensure safe seismic performance
under design accelerations.2
Design, Specify, and Install Drift Joint
Accessories That Do Not Have a Lower
Pocket and Are Designed to Weep
If it is determined that horizontal drift
joints cannot be eliminated in a stucco sys-
Photo 2 – This photo shows the typical drift
joints (along the top of the windows in the
lower portion of the photo) terminating at
the window jambs and forcing moisture
into the WRB, leading to uncontrolled
ingress of moisture behind the stucco and
leakage into the interior during heavy rain.
Photo 3 – Horizontal #40 drift joint
intercepts water running down the stucco,
which then flows back into the joint and
into the pocket of the lower accessory. Note
that stucco against the metal jamb flange is
actually trapping moisture, which is behind
it in the drift joint lower pocket. Problems
also exist with the upper stucco being able
to weep effectively.
tem, design the joint to shed moisture (see
Detail 1). Another type of horizontal driftexpansion
joint that provides a different
look similar to a reveal can be considered
(see Detail 2).
Two-piece expansion joints formed
with back-to-back double casing
beads with flexible membranes
mounted behind the joint move in
two planes, and when caulked utilizing
a backer rod and a quality silicone-
caulking material, are generally
much more water-resistant than
the standard mechanical two-piece.3
If using a type #40 drift (expansion)
joint, or if one is in place and it is contributing
to leakage, apply a backer rod or
backer tape into the joint to block ingress of
moisture into the pocket. Make sure to seal
off the ends and butt joints (see Detail 3).
In any expansion-drift joint accessory, it
is important to pay attention to the treatment
of the butt joints between pieces and
the ends. In addition, the weather-resistant
barrier and peel-and-stick membranes need
to be effectively integrated and terminated.
Change From the Conventional Internal
Drainage Plane System to a Drainage
Cavity Wall System
Another consideration is to design the
stucco system as a drainage cavity wall system
rather than a conventional internal
drainage plane system. Separating the
cement plaster cladding from the weatherresistant
barrier enhances the wall system’s
ability to resist the infiltration of moisture
that gets past the cladding, should an
accessory joint fail.
Conventional three-coat plaster wall
cladding systems with the common #40
two-piece horizontal seismic/drift/ex –
pansion joints are prone to leakage due to
Detail 1 Detail 2
Photo 4 — Field water testing of #40 drift joints caused leaks. After remediation by
installing sealant, subsequent field water testing did not result in leaks.
30 • I N T E R FA C E MA R C H 2011
uncontrolled moisture intrusion from water that is intercepted by
the joint, collected in the lower pocket, and which then travels horizontally
to leak at ends and corners. Also, upper metal accessories
that do not provide continuous weepage contribute to the
failures by collecting moisture and exacerbating the condition by
trapping moisture in the wall system, which travels horizontally to
leakage points.
Existing installations utilizing the #40 two-piece expansion
joint should be remediated by the application of a backer material
and sealant along the entire length of the expansion joint to prevent
moisture from penetrating into the lower pocket and into the
wall (Detail 3).
1 Daniel Lemieux and Paul Totten,
“Building Envelope Design Guide —
Wall Systems,” Whole Building
Design Guide, Wiss, Janney,
Elstner, Associates, Inc., updated
2 Chris Arnold, “Seismic Safety of the
Building Envelope,” Whole Building
Design Guide, Building Systems De –
velopment, Inc., updated 11/18/09.
3 Gary Maylon, “Expansion/Control
Joints: The Most Controversial
Metal Lath Accessory,” Walls and
Ceilings, 12/1/03,
MA R C H 2011 I N T E R FA C E • 3 1
Bob Craig, a project manager with Allana Buick & Bers, Inc.,
has 20 years of experience in the construction inspection and
design field. He has a BA in architecture from the New Jersey
Institute of Technology and a BS in business management
from Montclair State University. Craig specializes in building
envelope inspections and investigations as well as peer review
and design. He holds registrations as a building inspector
and electrical inspector from ICC, as a Construction Doc u –
ment Technician from CSI, an EIFS Inspector from the AWCI,
and a Registered Roof Observer from RCI.
Robert Craig, RRO, CDT
Photo 6 – Water leakage was occurring universally at the building
interiors at the outside corners. This view shows the painted joint
and stucco. The paint did not effectively seal the joint from water
accumulating in the lower joint pocket and leaking out at the butt
edges—first onto the WRB and eventually into the interior.
Detail 3
Photo 5 – Excessive uncontrolled water leaking out of the ends of the
lower pockets at window jambs resulted in moisture intrusion
through fasteners and into the interior of the building.