Hardwood Floors December 2025/January 2026

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

DO WE REALLY NEED SO MANY DECIMAL PLACES? In Table 13-5 of the 2021 Wood Handbook, DCCs are listed to five decimal places; for example, the familiar tangential DCC for commercial red oak is reported as 0.00369. We determined that, based on how DCCs are calculated, and in practical terms, reporting DCCs to four decimal places is scientifically and practically justified. Our example above would thus be a more wieldy 0.0037 instead of 0.00369, with no meaningful change in calculated values (that is, the 0.00001 difference in value doesn’t amount to much, practically). We didn’t complete our paper in time to make this change in the 2021 Wood Handbook, but we expect to update the DCC values the next time the Wood Handbook is updated. VARIABILITY All of these findings address underlying concerns we had about how best to use DCCs in the real world. As wood scientists, we know that any individual board of a given species is going to have its own properties, though those properties are likely to be within the normal range of variability for that type of wood. It is somewhat like meeting a dog on the street – if it is a rat terrier, you probably have certain expectations that it will be an energetic dog, but each rat terrier will have its own personality within that range of expected traits. So, to have a single number like a DCC and apply it equally to all boards of a given wood and expect it to correctly predict the shrinking or swelling of that exact board is unreasonable and not supported by experimental data – it doesn’t account for natural variability. Nonetheless, we would expect that, averaged over an ever increasing number of boards, the DCC would accurately predict the shrinking or

Calculating a dimensional change coefficient

If you need a DCC for a certain wood species but there’s no published value, our calculator may be able to help. You need two pieces of information to use the calculator: the fiber saturation point (FSP) and the total amount of shrinkage from the

green condition to the ovendry condition for your new wood. The relationship between shrinkage and MC is roughly linear between 6 percent and 14 percent MC (see diagram). The FSP refers to the MC at which shrinkage starts – for many woods, the FSP is around 30 percent, but it can vary appreciably. The chart above shows the relationship between shrinkage and MC.

Example calculation

Below is a calculated tangential DCC for wenge (Millettia laurentii) using data from the TROPIX 7 Database, where the FSP is listed as 22 percent and total tangential shrinkage is listed as 9.1 percent. These values are entered into the calculator (light green cells), and it gives a DCC value of 0.0044 (dark green cell).

Where do you find values for the FSP and green-to-ovendry shrinkage?

There are several online references available: • FPL Wood Handbook, Chapter 4: https://research.fs.usda.gov/treesearch/62243 • TROPIX 7 Database: https://tropix.cirad.fr/en/technical-sheets-available • The Wood Database: https://www.wood-database.com/

• Hardwoods of North America: https://doi.org/10.2737/FPL-GTR-83 • Softwoods of North America: https://doi.org/10.2737/FPL-GTR-102

• Tropical Timbers of the World: https://research.fs.usda.gov/treesearch/69634 If these don’t have values for the wood species of interest, try an internet search for other publications.

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