Ascent, a 25-storey luxury apartment building in downtown Milwaukee, Wisconsin, is the tallest mass timber building in the world, surpassing Norway’s 85.4m tall Mjøstårnet by a meter. A special feature of the high-rise is that some of the wooden structural elements will be visible in living areas.
From the moment it was announced throughout construction, Ascent’s progress was closely watched, not just by industry insiders, but also local and international media. Its permitting process was reported in detail, as were the stages of construction, from the pouring of the cement foundation to the delivery of modular timber components from Austria.
The fact that Ascent’s vertical journey is a sensation has a lot to do with the wide appeal of living in the beauty, warmth, and natural sustainability of homes made of wood, and to the rarity of mass timber buildings above a certain height, especially with visible wooden beams and panels.
With changes coming in the 2021 International Building Code, the rarity factor may diminish. The ANSI/APA PRG 320 Standard for Performance-Rated Cross-Laminated Timber is widely seen as opening the door to taller timber buildings. The standard for cross laminated timber (CLT) makes provisions for several distinct types of office and residential buildings up to 18 stories.
KLH on a Growth Path in North American Market
Ascent’s CLT was supplied by Austria’s KLH Massivholz GmbH, a global CLT pioneer and market leader with more than 35,000 projects world-wide by April 2021. KLH’s products were approved in North America in 2019, meeting the region’s rigorous strength, fire safety, and durability tests. Due to the height and design of the Ascent project, KLH’s CLT had to undergo additional third-party tests and ratings, according to media reports.
KLH not only supplied CLT but also provided the project detail planning services for Ascent. It has a subsidiary in Portland, Oregon, KLH Holding Corp. It is part of KLH’s extensive international sales and engineering network, in addition to its capacity for high quality mass timber production.
KLH uses Henkel’s Loctite HB X adhesives, which were approved for the North American market in 2018.
“We established KLH in North America because of the demand for our CLT building solutions. There is a high potential to grow across the regional markets in North America. Working with Henkel to use HB X and certify our CLT products was both a rewarding and essential step on the journey. We are counting on Henkel as a partner as the market develops and expands,” said Sebastian Popp, Technical Director KLH US Holding.
Standards Evolution and Adhesives
Henkel Loctite is the only one-component polyurethane (1C-PUR) certified for CLT, glulam, and other engineered wood building materials in the North American market.
In North America, the PRG 320 standard defines fire-resisting characteristics and the so-called self-extinguishing properties to prevent delamination in the case of a fire. It also refers to the ANSI 405 “Standard for Adhesives for Use in Structural Glued Laminated Timber” which defines adhesive strength, durability, and moisture resilience, as well as the testing procedures and heat performance. Additionally, it defines both a small and a large-scale fire test.
The relevant standard includes test methods and requirements for both full-scale fire tests (so-called compartment tests) and small-scale testing for temperatures of up to 230°C.
As similar superior fire performance standards are emerging in other markets, such as Europe and Australia, Henkel has certified certain products from its HB X series to meet the evolving demand. “We are proud to have certified our PUR adhesives on three continents” said Chrisoph Sturmlechner, Head of Sales Henkel Engineered Wood Europe.
Looking beyond the standards and approvals, Henkel strives to anticipate the needs of its mass timber industry customers, whether it is in the area of sustainability, durability, strength, user health and safety, or manufacturing efficiency.
“We work internally and collaborate externally to develop the kinds of products that enable our customers, like KLH, to grow, and drive the use of sustainable mass timber building materials around the world. Henkel has an enabling role for mass timber manufacturers active in multiple regions,” said Christian Fild, Global Head of Henkel Engineered Wood.
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