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Recommended ambient conditions in buildings are 30-50% relative humidity at 60-
800F. If ambient conditions stay within this range, the amount of expansion and con-
traction of wood floors and furnishings at 6-9% moisture content is limited. (Table from
US Dept of Agriculture “Wood Handbook, Wood as an Engineering Material”)
Relative Humidity, Wood Moisture and EMC Chart
Using Pin / Pinless Mode and Thermo-Hygrometer Function
Example: For a relative humidity of 35% and a temperature of 700F, the EMC is 6.9%. A wood
floor at 6.9% moisture content is stable, if the surrounding air has a relative humidity of 35% and
a temperature of 700F. In short a floor is stable, when MC and EMC are the same.
EMC Chart
Relative Humidity in %
Temp. 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 98
30 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.8 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3 26.9
40 1.4 2.6 3.7 4.6 5.5 6.3 7.1 7.8 8.7 9.5 10.4 11.3 12.4 13.5 14.9 16.5 18.5 21.0 24.3 26.9
50 1.4 2.6 3.6 4.6 5.5 6.3 7.1 7.9 8.7 9.5 10.3 11.2 12.3 13.4 14.8 16.4 18.4 20.9 24.3 26.9
60 1.3 2.5 3.6 4.6 5.4 6.2 7.0 7.8 8.6 9.4 10.2 11.1 12.1 13.3 14.6 16.2 18.2 20.7 24.1 26.8
70 1.3 2.5 3.5 4.5 5.4 6.2 6.9 7.7 8.5 9.2 10.1 11.0 12.0 13.1 14.4 16.0 17.9 20.5 23.9 26.6
80 1.3 2.4 3.5 4.4 5.3 6.1 6.8 7.6 8.3 9.1 9.9 10.8 11.7 12.9 14.2 15.7 17.7 20.2 23.6 26.3
90 1.2 2.3 3.4 4.3 5.1 5.9 6.7 7.4 8.1 8.9 9.7 10.5 11.5 12.6 13.9 15.4 17.3 19.8 23.3 26.0
100 1.2 2.3 3.3 4.2 5.0 5.8 6.5 7.2 7.9 8.7 9.5 10.3 11.2 12.3 13.6 15.1 17.0 19.5 22.9 25.6
Dimensional Stability of Wood:
Wood moisture and relative humidity are crucial factors
for dimensional stability of wood. Use the Ligno-DuoTec BW to measure both. If wood shrinks,
warps, cups, checks or delaminates, it always has to do with changes in wood moisture and/or
relative humidity. No shrinking and warping occurs, when an equilibrium with the surrounding air
has already been reached, which means wood is not losing or absorbing any more moisture.
Predictions and Explanations:
Measure relative humidity, temperature and moisture
content. Compare the measured values with the EMC chart above to predict, if wood is stable or
will loose or gain moisture.
-- A hardwood floor shows gaps from shrinking. The moisture content at the present time mea-
sures 6.2% and the rel. humidity is at 30%. The only explanation for the gapping is, that the
floor was installed at a higher moisture content. Once exposed to the dry air, the floor dried out
and the gapping occurred.
-- If a dry floor with a perfect moisture content of 6.2% is exposed for a long time to air with a
relative humidity of 60% at 700F, it can be predicted that the floor will absorb moisture until 11%
has been reached. Depending on the wood species, a 5% increase in moisture content can be
accompanied by a substantial amount of expansion.
No more surprises!
Use the EMC chart and your Ligno-DuoTec to predict problems. The
chart is also helpful to explain to your customers, why relative humidity in their home matters.