Originally Posted by
michael osadchuk
David.....You are absolutely right: your post drove me to back to read Bruce Hoadley "Understanding Wood" (first edition)...... and he clearly agrees with you regarding relative humidity typically being significantly lower indoors than outdoors in winter (and the reverse in summer) and because it is changes in relative humidity that directly affects equalibrium moisture content of wood which in turn cause wood movement......
.... for a real life example today I took outdoor temperature and relative humidity readings where I live (north of Toronto, Canada; snow melting after an early season snowfall): the temperature was 2 degrees Centigrade/34 degrees Fahrenheit and a relative humidity of 56%; I brought the weather gauge indoors (electric heating; no humidifiers) and the temperature was 22 degrees Centigrade/70 degrees Fahrenheit with the relative humidity reading being 33% - a drop of 23%...as you state, bringing wood from outside to indoors in such an instance would lead to a bit more wood movement (contraction).......
Hoadley also said temperature change ALONE has virtually no thermal expansion/contraction effect on wood;it is the change in relative humidity typically associated with indoor/outdoor and seasonal weather changes that has the big impact on wood.....
thanks for correction; reading Hoadley, though interesting, hurts my head (swollen head now shrinking...smiley)
Incidentally, I keep track of seasonal relative humidity changes in my basement workshop which is well insulated, has a bit of electric heat and no humidifier/dehumifier: the temperature typically stays above 60 degrees Fahrenheit and doesn't exceed 75 degrees, while the relative humidity can swing from a low of 20% on some days in late January and February to a high 65-70% on some rainy days in late summer; despite this wide swing in relative humidity, moisture readings on unfinished, kiln-dried wood stay between 6 and 10% year round