While admiring a Mass Timber building rising nearby, I wanted to find out if CMs can benefit from this business. Katerra apparently thinks so, first becoming a CM and later a CLT manufacturer. So far, the supply of CLT is limited – the Katerra plant is 2500 miles from this Virginia jobsite and the closest source for these parts was Northern Canada. I also wanted to know how the building owners got this new technology past our small-town Building Department, since we’re still on the 2015 International Building Code (IBC). To understand its potential, I took a walk through this unique structure, future home to Apex, Inc.
From outside appearances, this building is a typical timber post-and-beam construction like many in the distant past. [For photos, See PDF or View in Full Issue.] Today you may see remnants of these structures in the exposed beams of renovated retail spaces. But 100 years ago, industrial buildings of this type proliferated across the country, like the one that housed MiTek’s first stamping plant. Early codes recommended that they be built with solid sawn lumber with a “minimum cross-sectional area of 72 square inches.” Such thick members, like 6x12’s, are resistant to fires, as charring penetrates only the outer surfaces. But their prevalence was curtailed as the availability of such timbers diminished in the mid-20th century. However, the former West Coast Code, ICBO, retained the allowance for this “Type IV” construction and, later, the IBC carried it forward to the present day.
Upon closer examination though, the finely finished components of this structure bear no resemblance to the rough timbers of the old industrial buildings. And they are even larger in size. This is made possible by the innovative massing together of smaller pieces of wood to form larger and stronger components. Boards as small as 1x4’s, as shown here, are joined together to achieve a smooth, monolithic, and highly valued appearance. [For photos, See PDF or View in Full Issue.] This technology also enables fuller utilization of our timber resources, much like LVLs do but with the beauty of exposed glulams. These members are most effective spanning up to 25 ft. bays, and well suited to office buildings like this one, rather than industrial applications.
Unique to the Apex building and like structures is the inclusion of CLT floor panels. As their cross laminated name implies, they are built up of multiple layers of 2x members, laid crosswise to one another (note the alternating side grain and end grain in the enlarged detail). Many of these panels are clear-spanning over 20 feet, while others are supported by joist framing, though at wider centers than the old mill buildings.
CLT originated in Europe in the 1970s but wasn’t commonly used in the U.S. until the 2015 IBC, which piggybacked on the legacy Type IV construction. This allowed more Mass Timber structures to be constructed in the U.S. but with height limitations. Later, after several years of evaluation, those limits were sharply increased, permitting Mass Timber structures up to 18 stories tall in the 2021 IBC.
Also unique to Apex are the interlocking connections, similar but much more intricate than those found in Lincoln Logs. These details expedite assembly, minimize metal hardware, and reduce installation labor. They are a credit to the manufacturer, Nordic Structures, and the design engineer, Schaefer of Cincinnati, who have collaborated on dozens of Mass Timber projects. Both column and beam ends are milled to provide adequate bearing surfaces and conceal connections. The CLT floor panels are longitudinally notched about ¾” deep x 1.5” to receive a 1x4 (the darker board shown here) to tie them together. [For photos, See PDF or View in Full Issue.] This is a fine example of the unmatched workability of wood which lends itself to highly detailed offsite fabrication, not dissimilar to what is done in truss plants, but on a much more capital-intensive scale.
Apex Clean Energy built this magnificent wood structure in keeping with their eponymous mission. They selected the ideal carbon absorbing, renewable, and sustainable resource well-aligned with the green energy movement. Most of the wood structure will be exposed, except for the office floors that require sound deadening board overlain with ¾” gypcrete. William McDonough + Partners of Charlottesville designed the structure, incorporating solar panel arrays and numerous energy efficient features to gain LEED certification.
Although this building offers tremendous offsite construction opportunities, this capability requires huge investments. The 270,000 sq. ft. Katerra factory cost upwards of $150 Million. Unfortunately, the ingenious connection designs in the Apex building minimize the hardware potential. However, the compatibility of wood wall panels with the structure seems to offer the best fit for component manufacturers. As this building moves further along, I’ll review these opportunities.
My last word (for the moment) on CLT construction is this: as it raises awareness of the desirability of wood construction, we can assist with the positive spill-over to our industry, which should enable even taller structures to be built with wood trusses and wall panels.