By Rick Bergman & Steve Hubbard
One of the many benefits of wood floors is that the raw material used to make them — trees — is sustainable. Under good forest management, trees are replanted
before or after they are cut down. This process replaces the material that is harvested today and ensures it will be ready again for future generations to do the same. The same is simply not true for other flooring materials.
Products considered to be environmentally friendly are often referred to as being “green.” For a product to be considered environmentally friendly there must be defensible scientific evidence to support this claim. A popular approach is to conduct a life cycle analysis of the product.
A life cycle analysis is an internationally accepted technique used to assess the environmental impacts associated with a specific product or process. The analysis conducted for a product’s entire life cycle is often referred to as a cradle-to-grave (i.e., nature-to-nature) assessment. For wood floors, this includes capturing data for the following elements: the tree sapling sprouting from the forest floor; the maturing of that tree; the harvest and transport of that tree to the sawmill; transportation of the lumber to the flooring mill; and the processing of that lumber into a serviceable flooring product ready for transport, distribution, installation, use, maintenance, repair, and disposal or recycling.
A substantial part of a life cycle analysis is a life cycle inventory (LCI). Conducting an LCI is part of the science-based approach to addressing environmental claims for products and counter green-washing. LCIs include environmental and energy costs by analyzing life-cycle stages such as resource extraction, transportation, primary and secondary processing, final product use, maintenance, and final disposal. For an individual life-cycle stage, this is often referred to as a “gate-to-gate” assessment. In simplified terms, LCIs measure all the raw material and energy inputs and environmental outputs to manufacture a particular product. It is typical for wood products for the production life-cycle stage to have the greatest life-cycle impacts and have been the focus of previous analyses in the United States. In addition, the environmental information identified from these analyses would have the greatest effect on reducing overall life-cycle impacts for the products themselves.
Because there are two types of wood floors, and each is manufactured differently, two distinct life-cycle inventories must be conducted: one for solid wood floors, and one for engineered wood floors.
Solid Wood Flooring
The life cycle inventory for solid wood floors was published in 2008 by the University of Wisconsin Department of Forest and Wildlife Ecology (UW), funded by the NWFA. The research conducted for this study was performed applying the methods found in the Consortium for Research on Renewable Industrial Material (CORRIM) Research Guidelines, and the International Organization for Standardization (ISO) 14040/14040 standards to ensure consistent and comprehensive data collection
and analysis.
Typical manufacturing of unfinished solid wood floors includes seven processes. These include: shipping the lumber from the mill, drying, planing, ripping, trimming, moulding, and sorting. An eighth process could be added for prefinishing, but this process was not included in the scope of this study. Inputs and outputs for each of these unit processes were collected as part of the research.
Shipping the lumber from the mill. During this process, trucks transport the lumber from the sawmill to the flooring mill. Lumber is sorted by species, dimension, and grade, and then is stacked for storage. Inputs include fossil fuel for the lumber haulers and stackers. There are no outputs included in this process.
Drying. During this process, the lumber is stacked onto drying stickers in the lumber yard, which enhance air flow. The stacked lumber also may be end sealed and oriented within the mill yard to optimize air drying. Once air drying is complete, the lumber is loaded into a kiln to expedite further drying and bring the lumber to the correct moisture content. Inputs include fossil fuel for the lumber stackers and haulers, water to produce steam for drying, and electricity to run fans. Outputs include air emissions, including volatile organic compounds, also known as VOCs.
Planing. During this process, the lumber is planed to a uniform thickness. This process also produces a smooth face surface, which aids with grading and sorting. Inputs include fossil fuel for the equipment that delivers the lumber to the planer, and electricity to operate the machinery. Outputs include shavings and sawdust. These outputs are burned as fuel or are manufactured into other items like wood pellets or wood bricks.
Ripping. During this process, the boards are fed through a rip saw to create uniform widths. Inputs include fossil fuel for the equipment that delivers the boards to the rip saw, and electricity to operate the machinery. Outputs include shavings and sawdust. These outputs are burned as fuel or are manufactured into other items like wood pellets or wood bricks.
Trimming. During this process, the boards are trimmed to eliminate defects. The boards also are cross-cut to create desired lengths. Inputs include fossil fuel for the equipment that delivers the lumber to the trimmer, and electricity to operate the machinery. Outputs include trim materials, shavings, and sawdust. These outputs are burned as fuel or are manufactured into other items like wood pellets or wood bricks.
Moulding. During this process, the boards are end-matched and side-matched into tongue and groove flooring. Bevels can be added at this stage as well. Inputs include fossil fuel for the equipment that delivers the lumber to the moulder, and electricity to operate the machinery. Outputs include trim materials, shavings, and sawdust. These outputs are burned as fuel or are manufactured into other items like wood pellets or wood bricks.
Sorting. During this process, individual flooring boards are sorted by grade according to their visual appearance. Inputs include electricity to run scanners, conveyor systems, and other machinery. There are no outputs included in this process.
In summary, the study revealed that solid unfinished wood flooring has significant advantages. The first is that wood is a low-carbon neutral product, and the second is that wood sequesters carbon during its service life.
Engineered Flooring
In 2010, the University of Wisconsin Department of Forest and Wildlife Ecology again funded by the NWFA published a second life cycle inventory of prefinished engineered wood floors. The research conducted for this study was performed applying the methods found in CORRIM guidelines, and ISO standards.
Typical manufacturing of factory finished engineered wood floors includes eight processes. These include the log yard; bucking and debarking; block conditioning; peeling and clipping; veneer drying; layup; trimming, sawing, sanding and moulding; and factory finishing. Inputs and outputs for each of these unit processes were collected as part of the research to help the flooring industry identify ‘environmental’ hot spots along their product production chain.
Log yard. During this process, logging trucks pick up the logs harvested from the forest and transport them to the log yard. Logs are sorted by grade and size and are stored either in wet or dry conditions depending on the species and the season. When ready and needed, logs are transported from storage to the mill bucker and debarker. Inputs include fossil fuel for the log haulers and water and electricity for the sprinklers. Outputs include water that is released during the wetting process along with emissions from the trucks.
Bucking and debarking. During this process, the logs are bucked to the needed length, and bark is removed to expose the usable wood. Inputs include fossil fuel for the fork lifts or rolling stock, and electricity to operate the saw and the debarker. Outputs include material lost when cutting the logs to size, and bark. These outputs are burned as fuel or are sold as mulch.
Block conditioning. During this process, the wood is either placed into a hot water bath or exposed to steam, to soften the wood. This makes the wood easier to peel from the log. Inputs include fossil fuel for the equipment that loads and unloads the log, hot water or steam, and electricity to operate the machinery. Outputs include air emissions from the boilers providing heat for the hot water or steam.
Peeling and clipping. During this process, the logs are placed on a rotary lathe and sliced or peeled into veneer sheets. They are then clipped to the needed size. Inputs include fossil fuel for sheet haulers, and electricity to operate lathes, conveyors, clippers, grinders, and waste equipment. Outputs include material lost when peeling and clipping the sheets to size. These outputs are burned as fuel or are sold for items such as feedstock for other wood products.
Veneer drying. During this process, the veneer sheets are placed into large jet dryers or kilns to bring the sheets to the correct moisture content. Inputs include fossil fuel for forklifts, water or hot oil to produce steam for drying, and electricity to run fans. Outputs include air emissions, including VOCs.
Layup. During this process, the sheets are stacked with each veneer grain perpendicular to the one above and/or below it. The veneers are then glued together to form panels. Inputs include fossil fuel for the forklifts, and electricity to apply the resin and run the presses. Outputs include air emissions from pressing and heating processes, curing of the resins, and the boilers.
Trimming, sawing, sanding, and moulding. During this process, veneer panels are cut into unfinished wood flooring. Panels are trimmed to standard dimensions, sawn into individual boards, sanded, and then moulded into tongue and groove flooring. Inputs include fossil fuel for forklifts, and electricity to operate saws, sanders, conveyors, and grinders. Outputs include trim materials, shavings, and sawdust. These outputs are burned as fuel or are manufactured into other items like wood pellets.
Prefinishing. During this process, individual boards are primed, stained, filled, cured, sealed, and top coated. Inputs include electricity to operate drying ovens, conveyors, and dust collectors. Outputs include air emissions, including hazardous air pollutants, also known as HAPs, and VOCs.
In summary, the study revealed that factory finished engineered wood flooring has two significant advantages over non-wood substitutes. One is that wood is a low-carbon product because of its minimal fossil fuel consumption, and two is that wood sequesters carbon during its service life as flooring. This is not the case for other flooring materials.
In addition to these two reports, Dovetail Partners Inc. published a Life Cycle Assessment of Flooring Materials in 2009 comparing a variety of different flooring options. The report cites a 1995 study conducted at the Chalmers University of Technology in Sweden comparing linoleum, vinyl, and solid pine wood flooring. The research conducted analyzed production, transportation, installation, maintenance, and end-of-life disposal. The study conclusively showed solid wood flooring to have the lowest environmental impact of the three flooring types studied. The analysis also showed wood to be the environmentally preferable material even if the service lives of the three flooring types were the same.
Two other studies included in the Dovetail report, conducted by Peterson and Solberg in 2003 and 2004, compared oak wood, linoleum, vinyl, and carpeting. Wood was determined to have the best results for low greenhouse gas emissions and the best results for low environmental impacts.
Want to show your customers that wood floors are an environmentally friendly flooring option that is both renewable and sustainable? The NWFA Education & Research Foundation Life Cycle Analyses for Solid Hardwood Flooring and for Engineered Hardwood Flooring conducted by the University of Wisconsin prove it. The studies analyze the environmental impact of several flooring alternatives for harmful air emissions, water consumption, total primary energy consumption and product life expectancy.
Visit nwfa.org/life-cycle-analysis.aspx to learn more.
Rick Bergman conducts green building research on the holistic environmental impacts of wood products and novel bioenergy systems using life cycle assessment (LCA). Along with conducting LCAs for developing environmental product declarations (i.e., science-based eco-labels) for wood products and environmental building declarations for wood buildings, Rick is on committees for green building standards and codes. He can be reached at rbergman@fs.fed.us.
Steve Hubbard is lead consultant for Hubbard Forest Solutions LLC where he conducts life cycle assessment research on forest products and investigates manufacturing process improvement strategies for North American wood products producers. He can be reached at shubbard@uwalumni.com.