Part 2—Engineered Wood: The World’s Most Advanced Building Material
By Rick Reynolds and Paul van Winkle
While it’s difficult to improve on Mother Nature, progressive architects, engineers, builders, and manufacturers are introducing more and more advanced manufactured wood products into the built environment. From cross laminated timbers (CLTs), to glulam lumber and heavy timbers, to wood-concrete composite systems (WCCs), manufactured wood products are transforming how we approach the beauty, structure, and health and safety, of our homes and public buildings.
Moreover, engineered wood is beginning to replace steel in new residential and commercial applications where longer spans and taller structures demand great strength, flexibility, and sustainability.
But before going into the special attributes of these new engineered wood products, let’s remind ourselves why it makes environmental sense to be harvesting and manufacturing engineered timber in the first place.
1. Wood stores carbon. Trees need carbon dioxide to grow. They have the unique ability to absorb CO2 from the atmosphere and store it long-term in their fiber. To combat climate change effectively, we will need to find ways to sequester more atmospheric carbon for centuries.
2. Wood is renewable. Wood is the only building material that grows naturally and can be replenished. Since 1920, the net growth of harvestable timbers in North America has grown by billions of feet, while timber removal has been reduced both proportionately and overall. Every year for the last 50 years, less than 2% of the standing tree inventory in the US was harvested while net growth was 3%. And to ensure a healthy stock of harvestable wood in the future, wood product certification emerged in the 1990s to develop guidelines for responsible forest management.
3. Wood has a lower energy impact. Not only does it take less energy to produce timber, but also the net CO2 emissions of wood products are negative. Timber is a single source material. Steel and concrete require significantly more fossil fuels to extract the needed raw materials, as well as for the numerous processes required to manufacture steel and concrete.
So why live and work in buildings made with engineered wood?
1. Energy efficiency. Thermally, wood laminates are significantly more efficient than steel or concrete. The cellular structure of wood contains air pockets that limit the ability to conduct heat and the precise manufacturing of CLTs and other engineered timber limits air leakage. The result is a comfortable room climate that requires less energy to maintain.
2. Durability, strength. Unlike concrete and steel, engineered timber construction is lightweight, ductile, dimensionally stable, and expands and contracts minimally.
3. Fire resistance. Timbers, both solid sawn and manufactured (glulam) won’t ignite until they reach more that 480 degrees F. When they do catch fire, they develop a protective char layer. As such, large timber beams have better fire resistance than unprotected steel beams of similar size because the interior of the timber remains much cooler, longer. Timber can take the heat. And while timber stays strong, steel weakens as its temperature exceeds 450 degrees F. At 1400 degrees F, steel retains only 10 percent of its strength. Structural timber’s slow burn properties delay collapse, increasing evacuation time.
Engineered Wood/ Structural and Stability Advantages
Bensonwood uses Nordic engineered wood products in many of its homes and public buildings. So what about the specific glue laminates, FSC Certification, and sourcing of the wood in Bensonwood structures?
According to Jean-Marc Dubois, Director, Business Development-Nordic Structures USA, Nordic does not use any formaldehyde based glues in their production. Purbond (latex-based) and isocyanurate glues are used exclusively. As for bonding strength, within the built environment these glues are water resistant and stronger than the internal wood bond.
The actual laminating process, or “stitching” involves a combination of factors that comprise the family of engineered wood products, but all elevate performance over standard lumber and timber products. Engineered wood (glulams or other) benefit from a single source material dried to consistent moisture content between 10-12%, making it a very stable material.
In contrast, standard, kiln-dried lumber can be a mixed species assortment with a nominal average of 19% moisture content (spruce, pine, hemlock,-larch, Western white woods, etc.) that have varying pitch content, fiber strength, coefficients of variation, etc. Given that an average 19% moisture content can be achieved by a range of dryness from 10-35%, the performance of individual pieces will vary greatly. And, as the moisture content and COV(Coefficient of variation) differs, so does the shrinkage rate.
So, a single species engineered wood product in the form of beams, columns, or other elements, will have a relative stability performance increase that exceeds lumber by a factor of 10.
Cross-laminted timbers—or CLT panels—used in structural walls and other applications, go one step further in performance due to their cross laminations. The longitudinal lamellae withstand shrinkage of the transverse layers, and vice-versa, increasing product stability by another factor of 10. So in two short steps, Nodic is able to improve performance over conventional lumber by a factor of 100.
FSC and Sourcing
Again, according to Mr. Dubois of Nordic, all material provided to Bensonwood can be fulfilled with FSC Certification, if specified. This includes all dimensional lumber (2X3, 2X4, as well as I-joists, glulam beams, columns, and CLT panels) certified sustainable by the Forestry Stewardship Council (FSC). The bulk of the engineered woods are comprised of 85% black spruce, 15% jackpine, and balsam fir and are sourced within a 200 km radius around Chibougamau, QC.
In a nutshell, this means wood—both solid sawn and engineered wood products—are faster to build with, offer better insulation properties, and require smaller foundations and build crews, leaving fewer local impacts. Beyond this, wood can create restorative environments that affect our well being, as we’ll see next in Part 3 of this series.