Building Safe with Cross-Laminated Timber

By: Hans-Erik Blomgren PE SE, Product Engineer, Structural Engineer


In July 2019, Katerra’s cross-laminated timber (CLT) manufacturing facility in Spokane Valley Washington reached a major milestone in producing its first CLT panel delivered for project use on the Catalyst building in Spokane. To make this date possible, Katerra has put over two years of focused effort into the definition of our product line and undergone substantial independent laboratory testing to ensure we meet the requirements of the International Building Code in the US and the Canadian Building Code in Canada. Katerra is committed to delivering quality products to our customers that fulfill the technical requirements of the building code across North America.

Below is a summary of the product testing we have performed to ensure our product is safe for use by following the ANSI/APA PRG 320 Cross-Laminated Timber Manufacturing Standard referenced in the International Building Code and the Canadian Building Code.

Katerra CLT Pilot Press located at Washington State University allowed Katerra to manufacture over 100 6ft x 12ft format panels for product certification testing while the factory was being constructed.

Adhesive Bond Integrity


Cross-Laminated Timber is a composite engineered wood product where the adhesive bonding quality between each lumber lamination is essential.  To assure bondline quality, the CLT panels we produce are regularly sampled in our factory’s Quality Assurance laboratory for small scale shear block testing.  These tests destructively fail the bondline of the specimen in shear, and the resulting failure surface is visually evaluated to ensure the majority of the failure plane is through the wood fiber and not the adhesive itself.  Additional samples are also taken and subjected to rapid water impregnation and drying in the lab.  These samples are then visually evaluated to ensure there is limited to no separation at the adhesive bondline to ensure an appropriate measure of moisture durability in field applications.

Katerra has also selected a face bonding adhesive for our CLT that benefits our manufacturing process.  Importantly, the manufacturer of this adhesive has certified its adhesive to meet the requirements of AITC 405 Standard for Adhesives for Use in Structural Glued Laminated Timber.  Our adhesive has also passed the recently adopted test method in the 2018 ANSI/APA PRG 320 standard that demonstrates the adhesive does not delaminate under compartment fire conditions as the charring front passes through the bondline.

To assure bondline quality, the CLT panels we produce are regularly sampled in our factory’s Quality Assurance laboratory for small scale shear block testing.

A shear block specimen after texting exhibiting a high level of wood failure at the adhesive bondline.

Mechanical strength and stiffness properties


Once bondline quality is assured, the cross-laminated timber panels are subjected to independent laboratory destructive testing to ensure their mechanical strength and stiffness testing properties are equal to or greater than the design values listed in our product research reports 0126 and 0126 CAN.  These design values are essential inputs for structural calculations performed by designated design professionals for each specific CLT building application.  Over 400 specimens of Katerra cross-laminated timber product have been individually tested to accomplish this.  The design values for our CLT product currently include:

  1. Major Axis flexural and shear strength and stiffness
  2. Minor Axis flexural and shear strength and stiffness
  3. Edgewise (in-plane) shear strength

Katerra CLT product testing (from left to right) 1) Flatwise flexural strength, 2) Edgewise shear strength, 3) Flatwise shear strength

Fire assembly performance


Katerra CLT can be specified for use as an exposed floor or roof element in construction types that allow combustible construction and require a 1- or 2-hour fire-resistive rating.  The 2-hour rating demonstrates that Katerra’s CLT product meets the requirements for the recently 2021 International Building Code Tall Wood Building provisions. 

This has been accomplished by subjecting our CLT panels, and their edge connections, to independent laboratory large scale horizontal furnace testing to the requirements of ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials.  This stringent test method requires the structural product to be fully loaded and endure exposure to furnace temperatures over 1,500F (815C) for 1-hour or 2 hours.  Katerra has successfully completed testing for the following assemblies on bare CLT panels with half-lap and spline joints:

  1. 1hr – Floor assembly Layup K5-0540 (half-lap and spline joints)
  2. 1hr – Roof assembly Layup K5-0540 (half-lap and spline joints)
  3. 2hr – Floor assembly Layup K-0630 (spline joint)

Applied load for large scale horizontal furnace fire-resistive rating testing. 

Visual examination of floor spline joint testing cross-section post-fire test.

Build with Katerra CLT


We are committed to ensuring that CLT will become the backbone for future generations of high-performance, low carbon buildings. With Katerra’s first CLT factory now in production, the transformation is just beginning.

Katerra CLT is available for Katerra-built as well as third-party projects. Reach out to CLT@katerra.com for additional information.


About the Author


Hans-Erik Blomgren PE SE, Product Engineer, Structural Engineer

At Katerra, Hans-Erik is the director of mass timber products and building systems. He has helped manage Building Code Compliance certification for the company’s cross-laminated timber product line which is manufactured at a new 270,000 sq. ft factory in Spokane Valley, WA.  As well, he has led Katerra’s efforts to technically justify and test cross-laminated timber panel assemblies and systems for code-compliant fire, structural, seismic, and acoustic use. Hans-Erik represents Katerra as a voting member on the ANSI/APA PRG 320 CLT Manufacturing Standard and ANSI/AWC Wood Design Standards code writing committees.

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