ASHRAE Journal - February 2013 - 61

F) Install flashing tape at head; G) Install sheathing tape over flashing tape at head to terminate flashing tape; H) Interior view prior to window installation; I)
Interior view after window installation; J) Air seal window around entire perimeter on interior with sealant and sealant backer rod.

such that variables such as softness,
hardness, low temperature flexibility
and adhesion strength can be optimized.
What all this means is that today’s
acrylic tapes can handle the movement
of the wood-based sheathings and foam
2/3
1/3
sheathings–mostly because they move
in tandem with the sheathings as opposed to fighting them.Coefficients of
expansion are “tuned” to the substrate.
The elasticity of the adhesive compensates for the movement of the substrate
due to changes in temperature and Photo 14: More Termination. With flashing tapes we tend to terminate them two
moisture content.
ways—with either a sheathing tape or a bead of sealant. A sheathing tape does not
The “flashing” tapes are typically butyl need to be terminated— it terminates itself. Figure 4: Termination of Flashing Tape.
rubber based (some are acrylic based as The “red” horizontal tape is a butyl based “flashing tape” that is “terminated” by a
previously mentioned). The rubbers are “green” acrylic based “sheathing tape.”
synthetically produced and thus like the
acrylics are also “tuned” to enhance performance. They are
sealant in the joint covered with a mesh reinforcing then all of
formulated compounds that allow you to add “tackifiers” to
this painted over. But then again I am old school on this stuff.
improve adhesion.
Back to this termination thing. With flashing tapes we tend
Both acrylics and butyl tape systems have UV stabilizers
to terminate them two ways: with either a sheathing tape or a
to address solar exposure and antioxidants to address long
bead of sealant (Photo 14 and Figure 4). A sheathing tape does
term aging which can change properties over time. In a twist
not need to be terminated; it terminates itself.
to typical perceptions the tape systems tend to be as durable,
At the end of the day, taped sheathings work as well as
or more durable, than the building wraps and housewraps they
building wraps and housewraps and vice versa. But there
are adhered to.
are limitations to both. With building wraps and housewraps
With any tape, for it to function well it must be firmly pressed
the biggest single problem is making sure gravity laps are
into place. This is particularly important with acrylic tape sysactually used. Amazing as it seems reverse lapping is still the
tems. They should be installed with a roller.
most common residential construction defect I see (Photo
What’s next? We see it already in the commercial side. Seal15). Despite all the education and training in the world it
ants and “paintable tapes” replacing tapes entirely. Installing a
still happens…go figure.
sealant in the joint and then painting over or spraying over the
With tapes the biggest single problem is folks thinking they
joint sealant. Sometimes a mesh reinforcing is used, sometimes
can stick them to muddy, dirty, cold, wet and frozen surfaces.
not. Sometimes just a spray applied tape. How are they working
You would think this is obvious. Again, amazing as it seems,
out? Ah, a little too soon to tell with some systems. I like the
folks keep trying to do it.
February 2013

ASHRAE Journal

ASHRAE Journal - February 2013

Table of Contents for the Digital Edition of ASHRAE Journal - February 2013