Storing kiln-dried lumber

Controlling the humidity in the atmosphere around stored lumber. January 16, 2002

Will wood that is kiln-dried absorb moisture and/or give up moisture quicker than wood that is only air-dried? We would like to provide a humidity-controlled storage building for our kiln-dried lumber, but can't afford it now. What is the best way to keep moisture content of milled and un-milled lumber in check? It seems that wood inside a "dead piled" pack of lumber has an okay moisture content compared to that on the outside.

Forum Responses
The US Department of Agriculture has a nice book on lumber storage. See the list of publications at WOODWEB's Bookstore:

Do you know that heating a storage area about 25 F above the outside low temperature will give you suitably dry conditions?

If you have a tight pile so that only 1% of the lumber is on the outside, plus the ends of all pieces (which pick up a little MC), maybe when you use this lumber the 1% or so of the pieces and ends will end up in 10% of the pieces that you are making and give you or your customer trouble. Storage is important.

Gene Wengert, forum technical advisor

Assuming the air-dried wood is as dry as it will get in your area - equal to the equilibrium moisture content (EMC) - about 12%. Assuming the kiln-dried wood is about 7%. The air-dried wood will not change because it is already equal to the EMC. The kiln-dried wood will approach 12%, gaining moisture. Both will end up at 12%.

If you can heat storage space, run the heat on a humidistat instead of a thermostat. You will find the temperature will run all over the place but it will keep the lumber dry. You can set some temperature limits for comfort, but this should not be workspace, just storage space. We get asked all the time about dehumidifying space to keep lumber dry. That can be done but is difficult and expensive. Heating is more practical.