Hardwood Floors December 2018/January 2019

AT THE SITE Expansion of White Oak (Continued)

and fastening systems (adhesive and/ or mechanical). Once assembled, the entire system begins to function as a unit. The subfloor is likely to be plywood or a reconstituted product, namely an oriented strand board (OSB). The properties of the reconstituted materials and impacts on the entire system vary depending on the manufacturer. Furthermore, all of these basic building materials are often subjected to non- controlled environmental conditions during storage and construction. Dimensional change (shrinkage) can then occur as the members adjust to climate-controlled conditions typical of an occupied house or commercial building. This change can affect the flooring itself. Daniel Cassens is Professor Emeritus at Purdue University. Brett Miller is Vice 3UHVLGHQW (GXFDWLRQ DQG &HUWLÀFDWLRQ 1DWLRQDO :RRG )ORRULQJ $VVRFLDWLRQ 1 1HLO 2VERUQ DQG 'DQ %ROORFN DOVR DVVLVWHG ZLWK WKH VWXG\ 1HLO 2VERUQ ZDV DQ undergraduate student in the Department RI )RUHVWU\ DQG 1DWXUDO 5HVRXUFHV 3XUGXH University at the time of the study. Dan Bollock is a Wood Laboratory Technician LQ WKH 'HSDUWPHQW RI )RUHVWU\ DQG 1DWXUDO Resources, Purdue University. REFERENCES Shmulsky, Rubin, and P. David Jones. 2016. Forest Products and Wood Science - An Introduction, Sixth Ed. Wiley-Blackwell. West Sussex, UK. [477 p.] U.S. Department of Agriculture, Forest Service. 2010. Wood Handbook: Wood as an Engineering Material. Gen. Tech. Rep. FPL-GTR-190. Madison, Wisconsin: Forest Products Laboratory. [508 p.] ADDITIONAL READING APA Technical Topics. 2016. Moisture-Related Dimensional Stability, TT-028C. 5pp.

gradient we often find within an installed flooring system over a crawlspace or unconditioned basement. The wood flooring was laid perpendicular to the length of the OSB panel. The RH in the environmental chamber ranged from 60-85 percent during the course of two months. The RH conditions outside of the environmental chamber (in the lab) ranged from 35-55 percent throughout the same period. Board width measurements were taken weekly and recorded. Measurements showed the wood flooring swelled as predicted based on the gain in moisture. What we did not expect was that the ends of the solid planks also opened up, resulting in end- joint gaps. After a thorough analysis, and taking into account the orientation of the wood floor in relation to the OSB, we determined that these gaps opened up in response to the subfloor swelling from the gain in moisture from underneath. This was backed by the fact that both OSB and plywood shrink/swell approximately twice as much in their width as they do in length. SUMMARY These two samples of solid and engineered wood flooring responded in a very predictable way. Moisture content change due to exposure to non-controlled environmental conditions resulted in significant dimensional change. The moisture content and amount of dimensional change depends on whether the sample was solid wood or engineered flooring. It is this moisture content and dimensional change of the flooring that is often focused on when problems develop. However, the visible flooring is only part of an entire system composed of joists or sleepers, subfloor, vapor retarders,

an NWFA Certified Installer). This installed panel then became the door to an environmental chamber. This allowed the testing to include different controlled conditions on both sides of the installed floor (as the door). The intention was to recreate the moisture

All photos courtesy of Dan Cassens & Brett Miller.

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