Engineered Wood

The biggest innovation in construction in the last 100 years

Hey There,

If you have been looking at buying a house in the past decade you might have noticed that prices tend to go up and down, but ultimately for the most part they go up. Getting new construction approved and built is challenging, but almost every new house or mid-sized apartment building these days is going to be dependent on engineered wood for both structural, roofing, and sheathing elements of the building. You might see a variety of oriented strand board, plywood, laminated veneer lumber, or cross-laminated timber being used in place of traditional planks such as 2x6s or 2x8s. If you want to furnish this home you might go to Ikea and buy low cost furniture that is mostly a combination of particle board or medium density fiberboard. Engineered wood is everywhere.

But what exactly is engineered wood and why should you care about it?

Engineered wood is just pieces of wood held together with glue. Wood is just a combination of three natural polymers: cellulose, lignin, and hemicellulose. The glue is synthetic polymer and it’s job is to hold together pieces of wood that would have once been considered scrap. Plywood is maybe the exception and it is usually different sheets of wood held together by phenolic resin. Those sheets of wood are basically shaved off of a tree and it’s why plywood cost so much. A sheet of plywood (and OSB) are sold in 4x10 foot sheets and this means that it’s great at serving as a wall to a structural frame. Old houses here in New England that get remodeled often expose their sheathing material, which was planks of wood nailed to the frame to form a wall. Plywood represents progress (now, if we can just get New Englanders to switch away from heating their homes with oil).

The problem with wood planks is that there are only so many trees out there capable of producing them. Plus, once they are cut and kiln dried they still have a tendency to warp or distort their shape due to changes in humidity. If our goal is to build more houses so the prices go down then lower raw material costs with increased performance what we want. The same is true for furniture. What was once hand crafted and joined together can now be mass produced in a factory. Note, some is still hand crafted and joined like it used to be, but robots play a bigger role. Also, glue is still important.

Oriented strand board (OSB), laminated veneer lumber (LVL), particle board, and medium density fiberboard (MDF) all are made relatively the same way. You blend a thermosetting polymer such as urea formaldehyde or polymethylene diphenyl diisocyanate with the loose pieces of wood in something called a blender. A gigantic blender that is essentially a giant rotating cylinder. The adhesive coated pieces of wood get some wax emulsion gets sprayed on (to help release the board from the press) and then they go to a conveyor belt. The mixture gets pressed into the boards with heat until the core of the board reaches the desired temperature and they are cut. If you are interested here is a good video from Georgia Pacific.

On average for OSB, particle board, and MDF the amount of polymer used to hold everything together is somewhere between 2-4% by weight of the wood. If that polymer is a phenolic resin or urea-formaldehyde resin there will be that formaldehyde will off-gas. There was a big issue with this post hurricane Katrina when a bunch of FEMA trailers used particle board that hadn’t had enough time to off-gas. My source on the reason for off gassing is a former co-worker and could be wrong, but I suspect he was right.

Much of the OSB recently has transitioned almost fully to polyisocyanates (pMDI), which has the benefit of not off-gassing formaldehyde after it’s been cured. When it comes to thicker versions of OSB such as laminated veneer lumber (LVL) or similar engineered wood products pMDI has a much bigger benefit in that steam preheating of the wood helps to polymerize it when the wood is pressed and get that target internal temperature much faster. Further, pMDI offers some benefits when it comes to productivity of the board mill and it cures to a lighter color, which some people find attractive.

In the end any sort of engineered wood is going to need a synthetic polymer of some sort to hold it together. Right now we get to choose from either formaldehyde based resins (phenolic, amino, or a mixture of both) or isocyante based resins (pMDI and polyurethanes). Both have benefits and drawbacks, but they are both derived from petrochemical starting materials. At least for now.

Some companies (mostly back integrated into forest products) like UPMBiofore have figured out how to start incorporating natural polymers such as lignin into their phenolic resins and it’s a useful technology to have when crude oil prices are high. Other companies such as Plantd are looking at hemp stalk fiber biomass to replace wood strands (I’m pretty sure they are using pMDI). Huber decided to put some water resistant paper on the outside of their OSB and developed a whole system to try and stop water intrusion into a house. Katerra tried to be the world’s largest cross laminated timber and modular home builder in the world, but went bankrupt instead. Softbank, I’ve got some pockets if you wanna put money into them.

Innovation in the space of engineered wood has the potential to re-define what wood is and how we use it. 100 years ago wood was something you got from cutting down a tree, but perhaps in 10-15 years its what we get from adhering agriculture byproduct to itself using carbon negative synthetic polymers not made from oil.

This is the way.

Tony