Is Cross Laminated Timber (CLT) Sustainable?

April 15th, 2020

Dear Readers,

Before we begin, here are a few key terms…

Cross Laminated Timber (CLT): several layers of lumber boards stacked crosswise and glued (or through other means of attachment) together to form sturdy, thick, structural panels.1

Sequester: to take ‘hold’ of. For example, trees have the ability to ‘sequester’ carbon as they grow, and release oxygen. Even if a tree is cut down, it still continues to ‘sequester’ that carbon. Once it is burned or it starts to decompose, it no longer ‘sequesters’ the carbon, and instead releases it into the atmosphere.

Sustainable: Relative. 

CLT Panel Configuration – CLT Handbook


Again, here is ‘sustainable’ being thrown around like a hot potato. When I first started researching for this blog, I self-defined the ‘sustainability of CLT’ as such: “If CLT continues to gain popularity as a construction material, will forests’ health then be put into jeopardy?” If I found the answer to this question to be, “no, forest health will not be affected if CLT continues to rise in fame” then CLT was, to me, considered to be ‘sustainable’.

As my research delved further and further, I realized that the ‘sustainability’ I wanted CLT to have, in my idealistic world, would be for CLT to not exist at all. And, not just CLT needed to be null and void, but the whole endeavor of the industrial revolution as well. And, not just the human will power to expand and explore needed to cease in order to achieve my idealistic self-defined ‘sustainability,’ but humanity overall. Harsh. I know. But I couldn’t help but think about how beautiful the forests could be if us humans hadn’t gone and trampled, cut, and tore through them.

However, as life would have it, us humans are here. Our urge to protect, provide for, and improve the lives of the ones we love inspires us to create, build, and advance the current states we find ourselves in. To survive cold winters, oneself and their family must find a way to stay warm. Living in a well-built home and burning wood (or other forms of fuel) to keep warm is one way of maintaining survival. Within that home, one may find pieces of paper. Upon said paper, there may be written or drawn ideas, dreams, hopes, inspirations, doodles, or academic endeavors. Beyond the papers are bound books. Within the books are gateways to other worlds and the enlightenment of minds. The papers are strewn on a wooden table top, the books sit upon wooden shelves; all useful pieces of furniture. We cannot deny the fact that as a human species, we have gained a lot of uses from our forests to protect, inspire, and educate ourselves and our families.

Given that spiel, the ‘sustainability of CLT’ cannot be measured in how popular the building material becomes. Instead, it must be measured according to the diligence and ethical environmental responsibility of foresters, loggers, companies, governments, communities, and individuals.

Through my research I discovered that ‘just leaving a forest alone’ does not necessarily mean you are leaving the forest to be healthier- especially after our previous human meddling. For one, forest fires can occur. During the winter months of late 2018 to early 2019, Washington state suffered multiple forest fires. One particular week that winter, 54 fires were counted to be burning. Kirk Siegler, a reporter for NPR, investigated how this environmental catastrophe was sparking a truce between environmentalists and Washington state’s timber industry: environmentalists were realizing that logging could contribute positively to a forest’s health, and the timber industry conceded that it could not simply cut down all the big, money making trees without posing a risk to the rest of the forest. Speaking to a local timber mill owner, Siegler explains that the timber industry is now “milling all the smaller-diameter younger trees that are densely packed into the forests.” These small, densely packed trees essentially act as kindlin’, and their removal eliminates the biggest fire risk to a forest. The small trees are also typically overlooked in traditional logging. But with the increase of popularity of CLT, which can glue smaller wood together and turn it into big beams and lumber boards, they are being turned into a marketable product.2

Biodiversity within a managed (or harvested) forest has also been claimed to be healthier than in a forest left untouched. There are five main forest ecosystems, or “stands”: savanna, open, dense, understory, and complex. These stands have existed even before human intervention, and many species have evolved to depend on the specific ecosystems. Because humans are a thing, we have created an imbalance of these forest stands, causing many species to face extinction. In order to return to a balance of ecosystems, active management is professed to be necessary in order to provide the diversity of stands; which means that certain parts of a forest should be harvested for wood products and fuel, and the harvest seasons should also be segmented in order to allow regeneration to occur, while the rest of the forest should be left as a reserve.3

Provided that forests have been and will continue to be harvested for lumber, CLT’s other environmental benefits become relevant. CLT, being wood, does have the ability to sequester (or hold on to) all the carbon the tree ‘sucked in’ during its lifespan. This makes wood ‘carbon negative’; which means that as a material it releases no carbon into the atmosphere during its life. Instead, it absorbs and holds onto that carbon until it is either burned, or it decomposes. And! Being wood, CLT has the possibility of being reused or recycled upon demolition.This makes using CLT in comparison to other building materials such as concrete or steel (which are carbon intensive in their formation) environmentally friendly.4 CLT also makes use of those small trees which enable forest fires, and also unwanted standing wood. Because CLT uses many pieces of lumber adhered together to make a solid, structural piece, the size of lumber that it uses can be small, and the grade of lumber can be lower. It offers the opportunity to use large swaths of forests which have been marred by insects or disease, rendering the lumber useful in the sense of creating a product as well as maintaining CO2 sequestration.5

However, all of the benefits of using CLT in construction is null and void if the forests are not harvested sustainably. Again, the ‘s’ word. Wanting to know what ‘sustainable harvesting’ looked like, I researched the Forest Stewardship Council (FSC). From what I found, they maintain an admirable diligence and duty to the forests they attempt to protect.

They remain vigilant of their forests by requiring those who seek their accreditation (typically those wishing to harvest a forest) to create a Forest Management Unit (FMU). Within their FMU, they must depict a thorough knowledge of the type and ecosystem of the forest they intend to harvest, as well as the species, plant communities, habitats, water resources, and soil types within said forest. They must also take into consideration within their FMU social impacts, such as traditional cultural resources and rights of use, public access to the forest, local and regional socioeconomic conditions and economic opportunities. And! The FMU must be revised to incorporate new scientific and technical information, as well as changing environmental, social, and economic circumstances. And! If it is a public forest being harvested, then the management plans must be made available to the public for review and comment prior to implementation.6 So, yes. They seem legit.

However! It comes down not just to the FSC to maintain the health of forests. But also to you. And me. The FSC is a voluntary standard for individual landowners and timber companies to uphold. It is not a government mandate. As consumers, we can choose to purchase FSC certified timber, thereby supporting their initiative to sustainable forestry. And as private landowners or small businesses looking to harvest from our forests, we can make the active choice to seek their certification and create our own FMU.

In conclusion, it would be a wonderful world if we did not have to exploit our forests at all. However, the human urge to create, expand, and provide for our communities prevail…and the alternatives for construction materials (and fuel) are worse and more detrimental to the environment. Wood is beautiful. It is raw. It even smells nice. If we can protect and cherish the forests, while also utilizing them for the resources they provide…then maybe we will achieve ‘sustainability’ for the day and age that we live in.


Shelby Aldrich

1. Karacabeyli, Erol and Brad Douglas. Cross Laminated Timber Handbook- U.S. Edition. FP Innovations, 2013. Page 3.

2. Siegler, Kirk. “Washington State Is Thinning Out Forests To Reduce Wildfire Risk,” National Public Radio, 23 Oct. 2019. Accessed on 4 March 2020.

3. Chadwick Dearing Oliver, Nedal T. Nassar, Bruce R. Lippke & James B. McCarter (2014) “Carbon, Fossil Fuel, and Biodiversity Mitigation With Wood and Forests”, Journal of Sustainable Forestry, 33:3, 248-275, DOI: 10.1080/10549811.2013.839386. Pages 252 – 253. 

4. Chadwick Dearing Oliver, Nedal T. Nassar, Bruce R. Lippke & James B. McCarter (2014), Pages 250-251. 

5. O’Connor, Jennifer M. Arch, Lisa Podesto, M.S., P.E., Alpha Barry, Ph.D., MBA and Blane Grann, M.Sc. “Chapter 11 Environmental Performance of Cross-Laminated Timber,” pages 443 to 493 of the Cross Laminated Timber Handbook- U.S. Edition. FP Innovations, 2013. Pg 11 (459). 

6. Forest Stewardship Council. “FSC-US Forest Management Standard (v1.0),” Recommended by FSC-US Board, May 25, 2010. Approved by FSC-IC, July 8, 2010. Accessed on 4 March, 2020. Pages 52-57.  NOTE: FSC-US Forest Management Standard (v1.0) is being revised (2018-2020 revision), and is expected to be done by 2021. 


  1. Dear Shelby,

    Firstly, I hope you and your loved ones are safe and well in these strange times.

    Thanks for sharing the article above, I found it to be very useful and informative. Good luck on your future initiatives.

    Merry Christmas and Happy New Year to you and your family.

    Kind Regards

  2. It hasn’t all been smooth sailing — several CLT panels cracked and collapsed during construction of an Oregon State University building in March 2018; plans for a wooden tower in Portland, Oregon, fell through — but the tailwinds behind mass timber are strong. A material that can be grown in abundance, creates rural jobs, reduces construction waste and labor costs, and slows the growth of concrete and steel seems like a win-win-win.

    • Hello, Jaryl! Thank you for reading and for also leaving a great comment! It is true…pursuing multiple story construction with CLT has not always been easy. And the push for making sure the wood is harvested sustainably still absolutely needs to be made! I actually just watched a Passive House Accelerator video from one of their Global PH Showcases: Passive Housing for Climate Refugees, ( The building is still in the beginning phases of design, but it is intended to be a seven-story project made out of NLT and NCLT panels…using wooden nails by the way!! In the video they discuss a bit of the structural integrity of mass timber as well as the sustainability and efforts to harvest responsibly. Because, really, what is the point in attempting to sequester carbon if you are going to destroy an entire forest to do so? In that case, the ends certainly do not justify the means!

      Gosh, I could keep talking about CLT forever! I’ll stop there 🙂 But thank you so, so much for reading!! And thank you for initiating a discussion!!! Please feel free to read and comment more! 🙂

      Kind regards,

  3. While items such as sawdust and wood-scraps are not as easily reused or recycled, they can be converted to energy through burning. Easy Demolition: Cross Laminated Timber is incredibly strong relative to its weight, it weighs just one fifth of reinforced concrete.

    • Yes! All of this is so true! The versatility of wood is unmatched~ and even if the wood can’t be recycled, reused, or mulched…it can still certainly be composted or, like you said, converted to energy through burning 🙂

      Thank you for reading!!


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© 2020 Sustaining Tree