Reply by Scsmith42

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Posted on Wet vs. Green vs. Dry

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125 posts in 2915 days

#1 posted 07-31-2011 05:18 PM

Rance and Topomax, ask and ye shall receive!

Knowledgeable lumber professionals have been trying to kill the “1 year per inch rule of thumb” for a long time, because it is so grossly misleading.

Actual drying time depends upon species, thickness, and local environmental conditions.

In the CONUS, probably 75% of all wood species dry at a rate significantly faster than “1” per year”. In fact, in most locations and for most species (slow drying species such as white Oak excepted) 4/4 lumber is well air dried within a couple of months, and six months for 8/4.

Lumber can and will start to degrade if air dried too long in an uncontrolled environment. Whenever lumber dries and then regains moisture, damage can and will occur (which happens frequently when AD outside and exposed to extreme humidity changes. Typical defects that result from excessive air drying are increased checking; warp, discoloration, etc, due from excessive cycles of rain and sun. If you’re a professional operation air drying in specialized drying sheds, you have more fudge room.

Here is a link to a US Forest Products Library publication that provides information about air drying tests performed in various parts of the U.S.

The information on page 4 is especially insightful about differences in air drying rates due to temperature and humidity. As an example, 4/4 oak stacked and stickered in early January required almost 5 months to dry down to 20% MC, yet similar species/thickness stacked and stickered on June 1 only requires 2 months.

One of the take-aways from this information is with respect to when to harvest and air dry. Due to the slower air drying rate for lumber stacked/stickered in the fall, if you’re going to dry a slow drying wood such as 12/4 oak then it would be best to mill, stack and sticker around October 1st in order to minimize defects.

When planning to air dry lumber, unfortunately there is no single hard and fast “rule of thumb. Rather, it is best if you first determine the species, thickness and associated maximum safe daily drying rate for your lumber. Step 2 would be to either mill, stack and sticker at the appropriate time (if a slow drying species), or to use the USFPL information as a reference to get an idea based upon the time of year and your location. Step 3 is to use a quality moisture meter to record actual MC% (once you are below 30% – meters are not accurate above that).

It’s really not that hard, it just requires a little more homework time up front.

-- Scott, North Carolina,

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