117CONTINUING EDUCATION
EDUCATIONAL-ADVERTISEMENTVaproShield designs and manufactures high-performance, mechanically attached, and self-adhered vapor-permeable
water-resistive-barrier (WRB) and air-barrier (AB) wall membranes and vapor-permeable AB roofing underlayments.
Combined with VaproShield’s flashing and rainscreen accessories, customers can create a total solution-based approach
to protect the building assembly from damaging moisture intrusion. http://www.vaproshield.comContinues at ce.architecturalrecord.combuild a wooden skyscraper in the coming
years. Wooden skyscrapers could be the
future for cities. There is a lot of potential
that’s unrealized for using timber at a very
large scale.”
Although the CLT building trend is
stronger overseas, North America is com-
ing on board with a 250,000-square-foot
mass timber manufacturing plant going up
in Spokane Valley, Washington, and another
227,000-square-foot CLT plant under con-
struction in Dothan, Alabama.
While the potential is exciting, this fairly
new renewable building type brings along with
it a unique set of building enclosure challenges.
As a moisture-sensitive material, wood is
slow to dry if wetted due to its hygric mass.
Furthermore, wetting for prolonged periods can
result in dimensional changes, moisture damage,
and microbial growth. As a result, keeping CLT
products dry during construction and through-
out the building’s service life is critical. The speed
at which CLT panels may be erected also creates
unique field challenges where CLT panels are
exposed to the elements for periods of time while
awaiting cover.
Filling this unique niche of providing water-
resistive-barrier (WRB) and air-barrier (AB)
membranes and roof underlayment, very few
technologies are ideally suited for the challenges
specific to mass timber construction.
One such technology is vapor-permeable
sheet membranes that simultaneously manage
bulk-water infiltration while allowing for ac-
celerated drying of the underlying materials.
As a self-adhered WRB that bonds directly
to wood substrates, no primers are required,
so the membrane installation can proceed
simultaneously with the CLT panel erection
process. This technology also lends itself to
WRB/AB pre-application, taking advantage
of the prefabrication process inherent to CLT
panel construction, and the quality control
and weather protection that shop fabrication
can provide.
MASS TIMBER
Before delving into the specifics of how to prop-
erly detail a CLT enclosure, some background on
this newer building material is helpful.
Modern mass timber buildings are con-
structed of engineered wood products, often
manufactured from multiple layers of sawn
lumber, attached to form a solid panel, beam,
or column. By forming solid wood sections,
mass timber differs from the conventional,
lightweight wood-framed construction that
has long dominated the low-rise residential
construction market in North America.
Among the mass timber materials known for
their sustainable, renewable properties, CLT is
the most popular. These panels offer strength,
rigidity, and dimensional stability, making
them ideal for f loor, wall, and roof applications.
CLT’s panelization potential also lends itself to
streamlining the construction process and dra-
matically shortening the construction schedule
while employing less labor
A number of other mass timber products
widely used across North America offer similar
benefits to CLT. They include nail-laminated
timber (NLT), dowel-laminated timber (DLT),
interlocking cross-laminated timber (ICLT),
glue-laminated timber (GLT), vertically
laminated veneer lumber (LVL), and laminated
strand lumber (LSL). Multiple mass timber
products can be used in the same building. For
instance, Figure 1-2 shows an example of a CLT
f loor supported by a GLT structure.While the primary focus of this course is
CLT building enclosure design, much of the in-
formation applies to other types of mass timber
products as well.
This course covers best practices for the
design and construction of high-performance
CLT wall and roof assemblies using suitable
vapor-permeable WRB and AB membranes,
roof underlayments, and f lashing accessories
in moderate to cold North American climates,
including International Energy Conserva-
tion Code (IECC) Climate Zones 4 through 8.
While CLT assemblies in warmer climates are
not covered, these building enclosure products
may still provide solutions for a successful
enclosure design in these regions. Of course,
these products can also be used with many
other forms of mass timber, wood-framed, and
conventional construction methods following
similar installation techniques and detailing.At the Hawker Architects-designed First Tech Credit Union in Palo Alto, California, a cross-
laminated timber (CLT) floor is supported by a glue-laminated timber structure.Figure 1-2