L14. Engineered Wood Products
As we have seen, wood is a great building material - it is renewable and is a way to capture and store carbon. Over the last two challenging lessons we learned about the dimensional stability of wood, degradation of wood by moisture and pests, and the strength limitations of wood. But what if we could put science and technology to work to improve the properties of wood to overcome some of these limitations?
Increasing the Value of Wood
As we have noted in past lessons, using trees is good and more land owners will grow trees if there is a market for the wood products. The more valuable the products, the more valuable the trees. And if trees have more value, more land owners will grow trees.
Using wood for energy is a low value use of the wood. In the energy market, wood competes with cheap fossil fuels. Traditional wood construction adds value to the trees because lumber has a higher value than energy. Paper also falls in this category of "higher value". But what if there were even higher value products? What if we could modify wood so it could compete with steel and cement construction or allow us to do other things? If we make wood last longer, increase its strength, or make it more dimensionally stable, we have a more valuable product. Engineered wood is the term used for all of the efforts to make wood into a higher value product. Engineered wood products include any wood product that goes beyond dimensional lumber.
Size, strength, durability, and aesthetics are some of the many enhanced features of engineered wood products.
Common Engineered Wood Products
(Much of the information in this section is drawn from APA Wood Links to an external site. or Wikipedia Links to an external site..)
Plywood: Remember how the wood is 20 times stronger in compression in the direction of the grain than perpendicular to the grain? Plywood makes use of that attribute by gluing thin sheets of wood together in opposite grain directions. The glue and the alternate grain directions give plywood strength in both directions. It also allows us to have large sheets of wood.
Veneer: The general term "veneer" means the outer thin layer. However, in the lumber business, veneer refers to the thin layer of wood taken off of a tree as in the video below. The wood can be softwood or hardwood. Often the outer layer will be different than the inner layers to get the desired external finish (e.g. a nice grain pattern from oak, birch or maple).
Here is a short video showing both the cutting of veneer. In this case they are making a marine plywood - plywood made out of wood that is water resistant to moisture and rot. Watch how they cut the veneer and assemble the plywood.
Oriented Strand Board (OSB): OSB "is a wood structural panel manufactured from rectangular-shaped strands of wood that are oriented lengthwise and then arranged in layers, laid up into mats, and bonded together with moisture-resistant, heat-cured adhesives. The individual layers can be cross-oriented to provide strength and stiffness to the panel. OSB is delivered in various dimensions, strengths and levels of water resistance." (Wiki: Engineered Wood
Links to an external site.)
Particle Board: "Particle board is manufactured from wood chips, sawmil shavings, or even sawdust, and a synthetic resin or other suitable binder, which is pressed and extruded. Oriented strand board, also known as flakeboard, waferboard, or chipboard, is similar but uses machined wood flakes offering more strength. Particle board is cheaper, denser and more uniform than conventional wood and plywood and is substituted for them when cost is more important than strength and appearance." (Wiki: Engineered Wood
Links to an external site.)
Fiberboard: Fiberboard (commonly referred to as MDF or Medium Density Fiberboard) "is made by breaking down hardwood or softwood residuals into wood fibers, combining it with wax and a resin binder, and forming panels by applying high temperature and pressure." (Wiki: Engineered Wood
Links to an external site.)
Engineered Wood Flooring: There are many types of engineered wood flooring. In general it is 3" to 4" width of particle board or plywood of various lengths with a thin veneer of hardwood. It is used in place of the much more expensive solid hardwood flooring, yet has the aesthetics and other features of hardwood flooring.
Composite Decking: "Composite decking is a man-made building product that includes an approximate equal mix of recycled wood fibers and recycled plastic. Because composite decking products are so durable and impervious to rot, they have a much longer lifespan than wood decks." (Fiberon) Links to an external site.
Glulam: Glued laminated timber, or glulam, is a product that glues dimensional lumber together to make a product that is stronger and more versatile than the original lumber. Glulam can be made in most any size and shape which allows designers to be very creative with building structures (like the photo on the right of the wood arches built using this technology). Similar technologies are Nail Laminated Timber (NLT) or Cross Laminated Timber (CLT).
Cross Laminated Timber: CLT refers to a specific Glulam technology with the alternating grains of the dimensional lumber. "A CLT panel consists of several layers of kiln-dried lumber boards stacked in alternating directions, bonded with structural adhesives, and pressed to form a solid, straight, rectangular panel. While at the mill, CLT panels are cut to size, including door and window openings, with state-of-the art CNC (Computer Numerical Controlled) routers. Finished CLT panels are exceptionally stiff, strong, and stable, handling load transfer on all sides." (APA wood. CLT Links to an external site.)
New Technologies
There are a variety of other similar wood products developed for specific applications. The two newest products are unlike the ones above. These two products are treatments to dimensional lumber and do not include glue or adhesive.
Thermal Modification involves heating the lumber to 180 C in the absence of oxygen. The process slightly burns or melts some of the lignin, cellulose, and hemicellulose. The finished product is more durable, more dimensionally stable, more water resistant, and darker in color than the original lumber. It is more brittle so is used as siding rather than as a structural component. Thermally modified wood was used for the siding of the U of M's Bell Museum on the St. Paul campus (photo).
Densified Wood is a very new technology that make the claim of being as "strong as steel". The technology was developed at the University of Maryland and involves compressing wood to about 20% of its original thickness. This technology is still in development. If you're interested in learning more, check out this article Links to an external site. in Nature - it also shows a pretty neat ballistic test.
We want to end this lesson with more with a bit more on a variation of CLT technology referred to as Mass Timber Construction. Listen as Michael Green, a global leader in this technology shares his thoughts on the benefits and future of wood construction.
Summary
The TED talk by Michael Green was done in 2013. A lot has happened in the last 5 years with more and more companies designing and building with Mass Timber Structures. The reflection in this lesson will give you a chance to dig deeper into this technology. But don't forget about all the smaller advances in wood technology that are being used each day in more traditional construction. It is an exciting time in the wood industry.
The biggest challenge with wood is making sure that wood is grown sustainably, both in the US and globally. We will look at this issue more in the next couple of lessons.