The Softwood Forest Products Buyer - November/December 2022

APA - Continued from page 2
The North American Difference
CLT design standards in the U.S. (the NDS) and Canada (CSA O86)
require that the CLT products meet the requirements of and be certified to
ANSI/APA PRG 320. When comparing North American CLT to products
manufactured elsewhere, it’s important to consider the following characteristics.
Design Property Compatibility
The design capacities published in ANSI/APA PRG 320 were derived
analytically using the lumber properties published in the NDS and CSA
O86. Imported lumber may have different characteristics, may not be
recognized in the NDS and CSA O86 and has published design values
that are incompatible with those of North American lumber. Therefore,
design properties for CLT products manufactured with foreign species
lumber should be carefully examined for compatibility with North
American CLT design standards.
Adhesive Heat Durability
The adhesives used in ANSI/APA PRG 320 CLT are required to meet
heat durability requirements to ensure the adhesives will not melt at elevated
temperatures. The heat durability of CLT adhesives is required by
ANSI/APA PRG 320 to be evaluated in accordance with ASTM D7247,
Standard Test Method for Evaluating the Shear Strength of Adhesive
Bonds in Laminated Wood Products at Elevated Temperatures, and the
CSA O177 flame test. Most CLT adhesives used outside of North America
have not been evaluated for heat durability. The use of adhesives that have
not been evaluated for heat durability could impose a serious life safety
concern in the event of a structure fire.
Moisture Durability
CLT moisture durability is required by ANSI/APA PRG 320 to be evaluated
based on the same accelerated aging (vacuum-pressure-soak) tests as
used for structural glued laminated timber (glulam), which has decades of
proven success in structural applications around the world.
The face-bond criteria (the minimum percentage of wood failure and
the maximum allowance for gluebond delamination after accelerated
aging tests) specified in ANSI/APA PRG 320 for CLT is the same as that
for glulam. These moisture durability criteria represent the most stringent
requirements in the world for CLT to ensure its long-term performance.
Most CLT products manufactured outside of North America have not
been evaluated to the same moisture durability and face-bond criteria as
ANSI/APA PRG 320. Since moisture durability of imported products
have not been evaluated to the same criteria as North American CLT,
long-term performance capability is unknown and may pose a risk of
decreased structural performance and increased delamination potentials
over time.
Fire Performance
Fire resistance of CLT products, when determined in accordance with
NDS or CSA O86, is based on the requirements that CLT products are certified
to ANSI/APA PRG 320. The rigorous adhesive qualification requirements
specified in ANSI/APA PRG 320 ensure the integrity of CLT under
the most severe fire conditions. New CLT adhesives are required to qualify
with full-scale fire test in accordance with ASTM E119, Standard Test
Methods for Fire Tests of Building Construction and Materials, in the U.S.
or CAN/ULC S101, Standard Methods of Fire Endurance Tests of Building
Construction and Materials, in Canada. This is not common practice
outside North America.
Most importantly, CLT products certified to ANSI/APA PRG 320-2018
or ANSI/APA PRG 320-2019 are required to use structural adhesives that
meet the requirements of the full-scale Compartment Fire Test (CFT)
specified in the standards and do not result in the char layer fall-off when
exposed to fire, which is known to cause a second flash-over and fire reignition.
The 2021 IBC and IRC and the 2020 NBC specifically require
CLT to be certified to these new standards. Therefore, it’s important the
designer, contractor and building official ensure the CLT products comply
to these new standards. Most CLT products manufactured outside
North America do not use adhesives that meet the stringent requirements
of ANSI/APA PRG 320-2018 or ANSI/APA PRG 320-2019 and
could result in a serious fire safety and code-compliance concern.
Always Look for the APA Trademark
The APA trademark is your assurance the CLT was manufactured by
North American producers whose products have been successfully qualified
and certified to ANSI/APA PRG 320. The ANSI/APA PRG 320
standard is recognized in the International Building Code (IBC) and International
Residential Code (IRC) in the U.S. and is required for using the
design provisions specified in the National Design Specification for Wood
Construction (NDS). In Canada, ANSI/APA PRG 320 is recognized by the
National Building Code (NBC) when the product is applied in designs that
meet the requirements of CSA O86, Engineering Design in Wood.
Find additional information in Cross-Laminated Timber—North American
CLT vs. Imported Product, Form S500 (www.apawood.org/publication-search?q=s500)
in the APA Resource Library.
About APA – The Engineered Wood Association
Founded in 1933 and based in Tacoma, WA, APA represents about 175
plywood, oriented strand board, glulam and cross-laminated timber, wood
I-joist, Rim Board® and structural composite lumber mills throughout
North America. Its primary functions are quality auditing and testing,
applied research, and market support and development.
Learn more at www.apawood.org.
AWC Continued from page 2
few radars in the design, fire, code and wood products industry, it’s important
for a variety of reasons.
The new FDS serves to consolidate different design provisions that were
scattered across a spectrum of design manuals, design aids and design
standards. The work over the last seven years to produce the FDS brought
all of those provisions under one roof, making it easier and more efficient
for designers, architects, fire service officials and code officials to find
exactly what they need to ensure wood-frame and mass timber buildings
meet the highest standards for fire safety.
In addition to bringing together existing provisions for the structural design
of unprotected wood members exposed to a standardized ASTM E119
fire exposure currently contained in the National Design Specification®
for Wood Construction, the FDS also provides calculation procedures to
address the added fire resistance and thermal benefits of protection provided
by use of additional wood cover, gypsum panel products, and insulation.
Calculation provisions have been developed to provide standardized
methods of calculating thermal separation and burn-through as required in
ASTM E119 and as provided in AWC’s Technical Report 10: Calculating
the Fire Resistance of Exposed and Protected Wood Members (TR10).
From the building code perspective, AWC maintains four other ANSIapproved
standards that are referenced in the building codes, and the
expectation is that the FDS will follow suit. Getting ANSI approval as an
American National Standard is a step beyond the minimum requirements
of consensus standards being recognized in the building code development
process, but does provide evidence to regulators that all steps in the
consensus process were followed.
Development of a standard under a consensus process provides transparency
and ensures the opportunity for meaningful participation by all
groups that are affected. A true consensus process also has procedures to
ensure balance, consideration of dissenting views and a process for appeals.
ANSI is the coordinator of the U.S. standards process and provides
strict objective requirements for accreditation of organizations, such as
AWC, following those processes. The ANSI process for establishing new
Continued on page 52
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