Hardwood Floors December 2025/January 2026

AT THE SITE Peek Behind the Dimensional Change Coefficient Curtain (Continued)

Putting these numbers into the calculator, we get an average MC of 13.0 percent at the time of manufacture:

But that’s not the whole story. Taking into account measurement uncertainty in MC and board width, manufacturing tolerance, and uncertainty in the DCC, we get an uncertainty of 1.4 percent in the MC at the time of manufacture, which translates to a range from 11.6 percent to 14.5 percent MC (the difference between 14.4 and 14.5 is a result of roundoff of 13.0 and 1.4):

To arrive at the result in the example above, we used the DCC calculator incorporating uncertainty. This is downloadable as an Excel file from FPL at https://bit.ly/fpldcccalculator. Using this calculator, you can take advantage of uncertainty in your calculations of dimensional change in flooring without having to worry about getting the math correct.

NOT SURPRISINGLY, FLOORS SHRINK AND SWELL A final component of our paper was time-lapse movies of wood flooring installed in test assemblies shrinking and swelling with changes in MC. Even through “everyone” knows that wood floors move, we were asked to document this process in test floor assemblies, so we constructed an entire humidity chamber within a room and collected time-lapse images of the assemblies (one oak, one hickory, one Acacia cf. mangium, and one Acacia cf. confusa). We assembled those images into movies you can download at https://bit.ly/fpldccvideos. DCCs are familiar but their origins vary, and experimentally determining DCCs for new woods is not trivial. Wood, as a natural material, is variable, and this variability influences the uncertainty in the parameters one measures or assumes at a jobsite. By using the DCC calculator we provide, you can incorporate realistic degrees of uncertainty into your calculations and make use of the best available science in your work. Dr. Alex C. Wiedenhoeft is a research botanist and team leader in the Center for Wood Anatomy Research at the USDA, Forest Service, Forest Products Laboratory where he has worked for more than 30 years, and is an elected Fellow of the International Academy of Wood Science. Dr. Samuel V. Glass is a research physical scientist in the Building and Fire Sciences unit at the USDA, Forest Service, Forest Products Laboratory, where he has worked for more than 20 years on moisture control and durability.

REFERENCES: FPL. 1974. Wood handbook – wood as an engineering material. Agriculture Handbook 72. Rev. August 1974. Forest Products Laboratory, Forest Service, U.S. Department of Agriculture. Washington, DC: U.S. Government Printing Office. FPL. 2021. Wood handbook – wood as an engineering material. General Technical Report FPL-GTR-282. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 543 p. https://bit.ly/fplwoodhandbook

Glass, S.V.; Boardman, C.R.; Ravindran, P.; Wiedenhoeft, A.C. 2022. Measurement and practical application of tangential dimensional change coefficients to hardwood flooring. Research Paper FPL-RP-711. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 22 p. https://doi.org/10.2737/FPL-RP-711 Markwardt, L.J.; Wilson, T.R.C. 1935. Strength and related properties of woods grown in the U.S. Technical Bulletin No. 479. Washington, DC: U.S. Department of Agriculture. NWFA. 2017. Moisture and wood. Technical Publication A100. St. Charles, MO: National Wood Flooring Association. Time-lapse videos of shrinking and swelling: https://bit.ly/fpldccvideos Dimensional change coefficient calculator: https://bit.ly/fpldcccalculator

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