Expansion Joints and Pre-Compressed Sealants
There a Gap in Your Air Barrier Wall Design? Overlooking joint sealing where it really matters--in the structural
day long, our Specification Development Engineering Team opens and reviews
architectural details. We look at hundreds of cross sections per week. One
of the most often seen reflects the industry’s move towards exterior wall
design based on
air barrier principles.
Driven by the desire for more energy efficient buildings, air barrier codes
have were developed and adopted in Canada years ago and have been adopted in
Massachusetts, Michigan, and Wisconsin with other states close behind. In
many other states, the principles of air barrier design are being widely
adopted because they make sense--building science, waterproofing, and
What do we see? One of the
details we see repeatedly shows a plan-section through the wall at a
structural expansion joint (see Figure 1). This can be at the mid-span or
elevation change of the building or, as commonly, at additions between new
and existing structures. The detail shows the structural backup wall,
sometimes block, sometimes steel-stud and exterior gypsum. The structural
wall is wrapped or coated with an air barrier membrane and extruded,
polystyrene insulation board is detailed over the air barrier. The
cavity-wall gap comes next and then the exterior façade material—often
brick, but also precast concrete, metal panels, etc.
the structural expansion joint in the façade we very often see
SEISMIC COLORSEAL—a structural expansion joint
hybrid sealant that fills these larger joints, insulates them, makes
them watertight, coordinates through color with the aesthetic of the
building, and installs without the use of invasive anchors.
Typical detail shows 2" expansion joint gap in precast
facade, wall cavity, extruded polystyrene insulation, air barrier membrane,
CMU backup wall. Note air barrier membrane
looped into joint and lack of insulation at the structural joint
in the backup wall.
Where’s the problem?
In the structural joint in the backup wall we see a sliver of air-barrier
membrane or other “tape” across or looped into the joint. The structural
joint gap itself is empty. On some details the gap is shown filled with something
usually fiberglass batt insulation. All three of the above are the
gap is a dynamic, moving, opening and closing structural expansion joint.
It will cycle continuously throughout its life. Air barrier membranes and
joint bridging “tapes” if installed without any slack will tear. Even if
installed as drawn with a loop into the joint, these products will
fatigue and tear where they wrap around the joint corners. These
materials are not designed to handle joint cycling and are particularly
prone to failure when they become brittle at low temperatures.
membranes and tapes provide no insulation. The detailing of extruded
insulation board in the cavity is intended to insulate the wall from the
outside of the structural wall. This means that at the
structural joint gap, instead of a thick piece of insulation board all
you have is a few mils of modified rubber sheet between the cold wall cavity
and the inside of the building. The structural joint gap
is a direct path to the interior of the building. In this detail,
the joint-gap constitutes a major gap in thermal insulation and could be setting the R-value for
the entire exterior wall system.
was pointed out in “Exterior Wall Systems, R-Value, and Revenue” by Tom
Kuckhahn published in the September 2003 Construction Specifier, heat
“seeks the path of least resistance, so the R-value of an actual wall is
closer to the R-value of the least insulating portion of that wall.”
Furthermore, in details where the structural joint gap is left unfilled,
condensation can form on the interior side of the membrane, thereby trapping
moisture in the wall.
use of fiberglass batt insulation to fill this cavity invites two problems.
Fiberglass insulation cannot handle joint cycling. It takes on
set and loses much of its insulation value. Once set and no
longer properly insulating, it is still porous and will absorb moisture that
condenses behind the uninsulated membrane “bridge” across the gap.
What to do?
An elegant solution to this gap in air-barrier wall design is to detail a
preformed, impregnated, cellular foam sealant in the structural joints in
the structural wall, as well as in the facade.
SEISMIC COLORSEAL is the product to use both in the backup and in the
facade. It is watertight, provides 100% movement capability, excellent sound
attenuation and, of course, R-value.
This means that on the above typical 2-inch joint, the
R-value at the structural joint gap sealed with
x 2.5 (the depth of seal of 2-inch SEISMIC COLORSEAL) = R-5.75.
On a typical 3-inch joint, the
R-value at the structural joint gap of a wall sealed with
x 3.5 (the depth of seal of 3-inch SEISMIC COLORSEAL) = R-7.52.
both sides of the interior wall, this value willdouble to R-15.04
excluding the R-value of the air-space created between the two pieces of
Design flexibility is
further extended through the option to customize the depth. With each
additional inch of depth, you are adding more insulation.
double-Sided SEISMIC COLORSEAL (COS-DS) provides the option to seal both faces of
a wall system in a single step. In this way you can eliminate the
interior wall cover as it would be replaced with the inner bellows face of
EMSEAL JOINT SYSTEMS LTD. 25 Bridle Lane, Westborough, MA 01581 EMSEAL LLC. 120 Carrier Drive, Toronto, ON M9W 5R1