Hardwood Floors December 2025/January 2026

By Alex C. Wiedenhoeft and Samuel V. Glass

If you haven’t wondered about some or all of these things, don’t worry, because we did. We are professional nerds whose jobs are to sweat the tiny details, and the Forest Products Laboratory (FPL) published a research paper “Measurement and Practical Application of Tangential Dimensional Change Coefficients to Hardwood Flooring” (Glass et al. 2022) asking these questions (and others), as a part of a cooperation between FPL and the Flooring Inspectors Education Guild. Our purpose with this article is to hit the high points of that report and give you the critical take-away messages we learned about DCCs. THE DCC ORIGIN STORY Where does a DCC come from? Let’s be explicit about the fact that DCCs are laboratory-derived values, but they are used in the real world every day. For some woods they were determined by painstakingly measuring rectangular boards with changes in MC (see the photo at right). For most woods, however, DCCs were calculated from green to oven-dry shrinkage values without any additional measurements of dimension between green and oven-dry. We address this in some detail in the paper, but the DCC is most commonly calculated by assuming a fiber saturation point and indexing the dimensional change value at 10 percent MC, which is in the middle of the range for in-service wood, and represents the most reliable portion of the shrink-swell relationship (see the “Calculating a dimensional change coefficient” sidebar on page 70).

A traditional experimental setup to measure dimensional change with changes in moisture content (from Markwardt and Wilson 1935).

DCCs were first published in the 1974 edition of the Forest Products Laboratory’s “Wood Handbook – Wood as an Engineering Material,” and have been reprinted in all subsequent editions and in wood flooring industry publications (e.g., “NWFA Moisture and Wood, 2017”). Whether determined with many measurements or calculated from green-to-ovendry shrinkage values, these old-school methods of determining a DCC are not practical for already-dry flooring of a new wood for which a DCC is not available. HOW TO DETERMINE A DCC FOR A NEW WOOD We compared a range of different ways to determine DCCs for new species by experimenting with two well-known flooring woods (red oak and hickory) and two woods for which DCCs were not available (Acacia confusa and Acacia mangium). All the permutations we examined are too soul-crushing to enumerate (gluttons for punishment, please see the full paper referenced at the end of this article), but in synopsis we found that our experimental method to determine DCCs from already-dry flooring boards gives values consistent with the DCCs for oak and hickory in the Wood Handbook, and are also consistent with calculated values for the two acacia species. Our suggested method involves at least 20 purely tangential (or radial for a radial DCC) test specimens from different boards (and ideally different trees), conditioning the specimens to several known MCs, making careful measurements of specimen dimensions, and using a regression equation in our paper to determine the DCC. All this is to say, determining a DCC for a new wood is not a quick or trivial undertaking if you want to arrive at a scientifically defensible value, and it cannot be determined from a single board.

the magazine of the national wood flooring association

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