RESEARCH BRIEF: Developing of a Lean Process Strategy for the Production of Thermally-modified wood

by Laura Cordoba, email

The wood market share includes environmentally friendly products such as thermally-modified (TM) wood. Wood products companies are working hard to create new products and to improve their production processes to satisfy their clients, meet financial goals, and to reduce their environmental footprint.

Siding: a TM wood application

Wood is commonly known for being a versatile renewable resource and in general is a non-toxic material. As a natural product, wood  must go through a value-added transformation to acquire the desired functionality. Thermal modification is a known process for this transformation, and it has been recently adopted by industries around the United States. This wood modification process is attractive for the market because creates a price competitive product, with great stability, increase decay resistance, and free of chemicals (Aro et al, 2014).

Thermally-modified (TM) wood has been available since the early 1990s in Europe, where it was developed as a substitute product to tropical hardwood lumber. TM wood is a product that is relatively new in the U.S. Therefore; consumers such as architects, engineers, building contractors, and end consumers are still hesitant about its potential and use (Wardell 2015). The fact that this kind of wood modification technique is new in the US provides chances to find improvements for the product and the process itself.

Lean thinking provides an opportunity to identify current problems that are affecting the manufacturing process of TM wood. Lean thinking is a business model that help managers to identify waste in the value stream of manufacturing, supply chain and services processes. Besides the presence of waste, long lead times, and high manufacturing costs are also part of the main concerns present in the manufacturing of TM wood. These issues could make a negative impact on the efficiency and effectiveness of the manufacturing process.

The first activity in the implementation of Lean Thinking in the production TM wood is to understand the production process. A mapping of the process is the first step following by the developing of efficiency and effectiveness metrics such as production rates, inventory levels, production costs, and lead times metrics. The second activity is to identify improvement opportunities and non-value activities on the manufacturing process of TM wood. The final activity is to design an improved production process that can help to solve the current issues. Lean thinking offers a variety of tools such as visual control, standardization of procedures, 5S, and plant layout that can be used to solve the issues and improve the current process.

A project like this requires to set up meetings, interviews, and walk-throughs to be able to map and obtain the required performance metrics to understand the current state of the process. Analysis of production data is also critical. The mapping of the process is conducted through value stream map (VSM). An Ishikawa diagram is also used to help understand the causes for the current issues. The future state or solution is also displayed on a new VMS culled the future VSM. In addition and economic analysis is conducted to tie the potential solutions to financial aspects.


  • Aro, M., Bradshaw, B., and Donahue, P. 2014. Mechanical and Physical Properties of Thermally Modified Plywood and Oriented Strand Board Panels. Forest Products Journal. 64(7/8):281-289.
  • Wardell, C. 2015. Thermally modified decking. Professional Deck Builder. June. pp:42-44


RESEARCH BRIEF: Green Construction and Sustainability in Wood as a Building Material

By Joseph Pomponi, Email:

Sustainability in building materials is a concept of using more biodegradable materials for construction projects. Sustainable development is described as enhancing quality of life and allowing people to live in a healthy environment and improve conditions for present and future generations (Ortiz, Castells, and Sonnemann 2009). “The improving social, economic and environmental indicators of sustainable development are drawing attention to the construction industry, which is a globally emerging sector, and a highly active industry in both developed and developing countries” (Ortiz, Castells, and Sonnemann 2009). To illustrate these concepts, the life cycle assessment helps evaluate the environmental load of products and processes. “The life cycle inventory (LCI) involves collecting data for each unit process regarding all relevant inputs and outputs of energy and mass flow, as well as data on emissions to air, water and land. This phase includes calculating both the material and the energy input and output of a building system. The life cycle impact assessment (LCIA) phase evaluates potential environmental impacts and estimates the resources used in the modeled system” (Ortiz, Castells, and Sonnemann 2009). Essentially, these analyses help with the life cycles of certain building materials and how these materials can impact the environment during their life in use and after they are able to be used for their purpose. The idea is to promote the use of more sustainable building materials such as wood, and engineered wood products as opposed to products such as steel and titanium. The wood materials tend to be more friendly to the environment, and helps towards reducing energy consumption. Carbon emissions are important to consider when deciding the sustainability of a building materials, as well as the life cycle of the certain material.

“Wood has many positive characteristics, including low embodied energy, low carbon impact, and sustainability. These characteristics are important because in the United States, slightly more than half of the wood harvested in the forest is used in construction” (Falk 2009). There is a difference in energy consumption when mining for materials needed to make products such as steel and other metals. Wood is seen to be easier to harvest and takes less energy to construct projects. The energy consumed in the construction of a steel-framed house in Minneapolis was around 17 percent greater than for a wood-framed house (Lippke et al. 2004). Below is a table discussing the designs of houses in Atlanta and Minneapolis and the difference of energy consumption between steel-framed and wooden-framed.

Table 1. Environmental Performance Indices for Above-Grade Wall Designs in Residential Construction (Lippke et al. 2004)

  Wood frame Steel frame Difference Change (%)b
Minneapolis Design        
Embodied design (GJ) 250 296 46 +18
Global warming potential (CO2 kg) 13,009 17,262 4,253 +33
Air emission index (index scale) 3,820 4,222 402 +11
Water emission index (index scale) 3 29 26 +867
Solid waste (total kg) 3,496 3,181 -315 -0.9
Atlanta Design        
Embodied design (GJ) 168 231 63 +38
Global warming potential (CO2 kg) 8,345 14,982 6,637 +80
Air emission index (index scale) 2,313 3,373 1,060 +46
Water emission index (index scale) 2 2 0 0
Solid waste (total kg) 2,325 6,152 3,827 +164

b % change = [(Steel frame – Wood frame)/(Wood frame)] X 100

Carbon plays a huge role in the earth’s ecosystem and in climate change as well. It is viewed as a negative impact on ecosystem sustainability. Forests play a huge role in balancing the Earth’s carbon cycle. Essentially, forests and other vegetation removes the carbon in the atmosphere through the carbon cycle. The process converts carbon dioxide and water into sugars for needed for the tree growth as well as releasing oxygen into the atmosphere. Approximately 26 billion metric tonnes of carbon is sequestered within standing trees, forest litter, and other woody debris in domestic forests and another 28.7 billion tonnes in forest soils (Birdsey and Lewis 2002). Different materials have different carbon emissions, table two shows carbon emissions of common building materials and materials used in construction.

Table 2. Net Carbon Emissions in Producing a Tonne of Various Materials (Falk 2009)

Material Net carbon emissions (kg C/t)a,b Near-term net carbon emissions including carbon storage within material (kg C/t)c,d
Framing material 33 -457
Medium-density fiberboard (virgin fiber) 60 -382
Brick 88 88
Glass 154 154
Recycled steel (100% from scrap) 220 330
Concrete 265 265
Concretee 291 291
Recycled aluminum (100% recycled content) 309 309
Steel (virgin) 694 694
Plastic 2,502 2,502
Aluminum (virgin) 4,532 4,532

a Values are based on life-cycle assessment and include gathering and processing of raw materials, primary and secondary processing, and transportation. b Source: EPA 2006. c From Bowyer et al. 2008; a carbon content of 49% is assumed for wood. d The carbon stored within wood will eventually be emitted back to the atmosphere at the end of the useful life of the wood product. e Derived based on EPA value for concrete and consideration of additional steps involved in making blocks.

From the table it can be seen that the carbon emissions of traditional building materials such as concrete, steel, and aluminum are greater than wooden framing material and medium-density fiberboard. The wooden materials also have a negative value of the near-term carbon emissions meaning the materials are more beneficial to the environment in terms of carbon emissions. Wood products have a low level of embodied energy compared to other building products and because wood is one-half carbon by weight, wood products can be carbon negative (Bowyer et al. 2008). Wooden building materials have a place for use in the construction industry. Wood materials in the end help with issues such as “green-building” and being more sustainable. These materials also have lower carbon emissions and in turn can potentially help reduce energy consumption of a building. Of course, fossil fuel-based products and metals are not renewable whereas in the forest resource is renewable. It is important for the wood products and forestry industry to have proper management of the forests to have sustainable harvesting for materials needed in the construction industry.

 Works Cited

  • Birdsey, R. and G. Lewis. 2002. Carbon in U.S. Forests and Wood Products, 1987–1997: State    by State Estimates. USDA Forest Service, General Technical Report GTR-NE-310
  • Bowyer, J., S. Bratkovich, A. Lindberg, and K. Fernholz. 2008. Wood Products and Carbon  Protocols: Carbon Storage and Low Energy Intensity Should be Considered. Report of    the Dovetail Partners, Inc.
  • Falk, B. 2009. Wood as a sustainable building material. For. Prod. J., 59(9), 6–12.
  • Lippke, B., J. Wilson, J. Perez-Garcia, J. Bowyer, and J. Meil. 2004. CORRIM: Life-Cycle Environmental Performance of Renewable Building Materials. Forest Prod. J. 54(6): 8-19
  • Ortiz, O., Castells, F., Sonnemann, G., 2009a. Sustainability in the construction industry: a          review of recent developments based on LCA. Construction and Building Materials 23          (1), 28–39

RESEARCH BRIEF: Yellow Poplar for CLT manufacturing

by Sailesh Adhikari, email

In North America, the structural use of the lumber is conventionally dominated by softwood species. In the past, hardwood species was studied for dimensional grading when grading techniques for structural timber has been implemented (Ding, 1987).  However, due to low economic advantages, hardwoods have never been successfully manufactured as structural lumber (Grasser, 2015) and left behind with traditional sawing practice of random length and width.  AHEC (2008) argued that because of low economic margin and sufficient availability of the softwood lumber and their mechanical properties to meet the design requirements, hardwood lumbers are never considered to standardize and continue to produce in random width and random length.  Though there has been some effort to use hardwood lumbers in dimensional construction.

Figure 1: Geographic range of yellow poplar in North America (USDA, 2015).

The first hardwood species which occasionally appeared on the structural market is yellow poplar (YP) (Green, 2005) because of some intrinsic properties of YP wood. Additionally, YP lumber is considered as easy to machine and plane which dry in faster pace compared to other hardwood species. Also, HMS (2013) reported that YP had shown stable connection and high quality finishing properties, that makes it more attractive for CLT application.

North American CLT standard and YP

CLT manufacturing with YP lumber is generally feasible as research and pilot projects have already proven (Slavid, 2013, Beagley et al., 2014; Espinoza et al., 2016). Given the intrinsic wood properties and existing ANSI/APA standard YP exhibits the properties to be considered as CLT raw material. The YP lumber properties and ANSI/APA standard are compared in Table 1.

Table 1: General requirements of North American CLT standards and Yellow- poplar lumber.

Requirements Standard YP Source
Recognized by the ALSC under PS 20 No (ALSC, 2010, ANSI/APA, 2012)
Specific Gravity, (0.42)  above 0.35 Yes (Bendtsen and  Ethington, 1975, ANSI/APA, 2012)
Minimum lamination grade major strength direction: 1200f-1.2E MSR; Visual No. 2 Yes (AWC, 2014, ANSI/APA, 2012)
Minimum lamination grade minor strength direction: Visual No.3 Yes (AWC, 2014, ANSI/APA, 2012)
CLT Grade for YP No (ANSI/APA, 2012)

Potential of YP lumber in CLT

Research conducted in Virginia Tech to utilize YP lumber in CLTs produce significantly positive results on the mechanical test.   Six 5-layer CLT beams (101” x 6” x 3.13”) have been fabricated and were tested non-destructively to complete this study.  The observed result concludes that the YP CLT is capable of matching strength requirements on effective bending stiffness (EIeff) and effective shear stiffness (GAeff) of the current North American CLT standard ANSI/APA PRG 320 (Mohammad et al., 2015).  Research conducted at the University of Trento in Italy examined into strength properties for CLT concludes that YP CLT has three times more strength and stiffness under rolling shear than other softwood species that is commonly used in CLT fabrication (Slavid, 2013).  The same research also concludes that yellow-poplar lumber is an ideal raw material source for CLT manufacturing given its properties.

The first YP CLT application in structure is Maggie’s Oldham from the UK, which is the world’s first building made from hardwood cross-laminated timber (CLT). Recently College of Architecture and Urban Studies and Department of Sustainable Biomaterial work together to construct a train observatory in Radford, VA registering as the first successful hardwood CLTs in structural application in the US.

Research and pilot studies conclude that technically and performance-wise YP lumber is a possible substitute or admix to softwood lumber, but there is some significant barrier to implement YP CLTs.   Most notable of all the significant barriers to successful hardwood CLT implementation is the efficient manufacturing of hardwood lumber produced to the CLT standard. Currently, hardwood sawmills are designed for appearance grade lumber production and not for the required CLT standard. In the dimensional aspect of current hardwood lumber production Quesada (2018) and Espinoza (2016) note significant findings compare to the CLT standard ANSI/APA PRG-320 2017.

  • The thickness of CLT layers should be between 5/ 8 inches and 2 inches, so lumber from hardwood logs should be sawn to a maximum of 2 inches thick.
  • For lumber to be used in the parallel load direction, the width should be greater than 1.75 times the thickness of the lumber, which excludes 2×2,2×3 dimensions. Lumber in perpendicular layers must have a width to thickness ratio greater than 3.5, which excludes 1×2, 1×3, 2×2, and 2×4 dimensions. Thus, the minimum possible lumber dimension can be 2X6.  Hardwood logs should be sawn to the dimension of 2X4 and higher for the parallel layer application and 2X6 and higher for the perpendicular direction.
  • All lumber to be used in CLT has to be surfaced on all sides and trimmed with 2% and below dimensional tolerance(ANSI/APA,2017).

Second major limitation of hardwood CLT implementation is the raw material price (Grasser, 2015).  The average price of the random length of YP lumber in March of 2018 was about $450 (AHEC, 2018), at the same time the average price of the southern yellow pine was about $360 (Madison Report, 2018) in North America. However, if we observe further, the price of low grade YP lumber, i.e., below 2com, the average price is less than $346 (AHEC, 2018). Thus there is an excellent opportunity to utilize lower grade YP lumber for CLT application.

The potential use of the YP in CLTs is an excellent opportunity to utilize the highly growing feedstock from the Eastern region of the US. At present, YP is one of the species that have a higher growth rate than harvesting rate, despite increased harvesting from the past.  Additionally, it grows from the plain of south Texas to the northern part of Canada, as shown in Fig 1, so there is an abundant resource available for this particular market. As the production of the CLTs for structural application grow to industrial level in the US, CLT manufacturer has to depend upon the traditional dimensional lumber species to meet the demands that will trigger the increased competition and potentially increased lumber price. Thus, YP lumber can be marketed from now as the additional raw material to the CLTs market so that both CLT manufacturer, as well as lumber producer, will be benefited with additional market opportunity.

The first step to promote YP lumber in CLT application is to manufacture CLT mats because at present situation, it is the standard product of all CLT manufacturer in the US and manufacturing CLT mats does not require to meet PRG 320 standard.  Such practice will help lumber manufacturer to find a new market and evaluate the cost factor to prepare the ready to use lumber for CLT application. On the other hand, CLT manufacturer with their manufacturing experience and capacity can work to establish the standard for the YP CLTs that will be crucial to recognize hardwood CLTs for the structural application.


  1. AHEC 2008. Guide to American Hardwood Products. Washington: American Hardwood Export Council.
  2. ANSI/APA. 2012. ANSI/APA PRG 320-2012 Standards for performance-rated cross-laminated timber. ANSI/APA, Tacoma, Washington. 23 pp.
  3. ANSI/APA. 2017. ANSI/APA PRG 320-2012 Standards for performance-rated cross-laminated timber. ANSI/APA, Tacoma, Washington.
  4. Beagley, K. S., Loferski, J. R., Hindman, D. P. & Bouldin, J. C. 2014. Investigation of hardwood Cross Laminated Timber design. World Conference on Timber Engineering. Quebec, Canada.
  5. Denig, J., Wengert, E. M., Brisbin, R., & Schroeder, J. (1984). Dimension Lumber Grade and Yield Estimates for Yellow-Poplar. Southern Journal of Applied Forestry, 123-126.
  6. Espinoza, O., Buehlmann, U., Laguarda, M., & Trujillo, V.R., 2016. Identification of research areas to advance the adoption of cross-laminated timber in North America. Bio-Products Business, 1-13.
  7. Grasser, K.K. 2015. Development of cross-laminated timber in the United States of America. Master’s Thesis, University of Tennessee, 2015. Retrieved from utk_gradthes/3479.
  8. Green, D. W., 2005. Grading and properties of hardwood structural lumber. Undervalued hardwood for engineered materials and components. Madison, WI: Forest Products Society.
  9. 2013. Species Guide – Poplar [Online]. Pittsburgh: Hardwood Manufacturers Association. Available:
  10. Mohamadzadeh, M., & Hindman, D. (2015). Mechanical performance of yellow-poplar cross-laminated timber.
  11. Quesada, H. (2018). Potential and limitations of using hardwood lumber as raw material for CLT. PowerPoint Presentation. West Lafayette, Indiana, USA. March 21, 2018.
  12. Slavid, R., 2013. Endless Stair – A Towering Escher-like structure made from American tulipwood CLT for the London Design Festival 2013.