Lumber dried in a kiln. The moisture content of small cross-section lumber can be reduced tp 12%. The moisture content has to be less than 14% for impregnated preservative to be effective.
Mills that have a kiln on-site have the option of artificially accelerating the drying process. Green timber is placed inside a large oven where heat removes moisture from the logs. They can suffer severe checking and cracking if the kiln controls are not properly monitored during the drying process. Use of a kiln can reduce the dry time required by the manufacturer in order for production, from many months to a number of weeks. Kiln drying usually results in an average moisture content of 18-20%, average being the mean moisture content of the outside of the log and the center of the log.
Since logs reach equilibrium moisture content when they are between about 6% and 12% (in North America), and since most kiln-dried logs are dried down to about 18% to 20% moisture content, kiln-dried logs can be expected shrink and settle over time, but to a lesser extent than green logs.