THE KILN DRIED LOG HOMES DIFFERENCE

In recent years the log home industry has seen a steady increase in the number of log home manufacturers offering its clients kiln-dried logs as an option.  Some companies have even made the commitment to offer only kiln-dried materials.  This movement was initially challenged by skeptics who claimed that moisture could be removed from the external sapwood, but not deep inside the heart of the timber.  Thanks to a few kiln-drying pioneers in the log home industry, these initial assumptions are now changing.

The process of kiln-drying logs is the science of carefully controlling the extraction of moisture from wood at a rate which will not cause damage to the wood.  When drying large logs, a stack of cants is placed in a sealed building with the equipment necessary to control the conditions needed to season the timbers.  These conditions are the same for air-drying lumber, namely; air movement, temperature, and humidity.  Once the material is in the kiln, the temperature is slowly raised to an eventual 170 degrees Fahrenheit.  Heated air is used primarily to speed up the evaporation of the moisture in the wood.  Warmer air will absorb a greater amount of moisture as it flows over and around the green lumber.

Large reversible fans circulate the heated air and change the direction of the air-flow at regular intervals to help maintain a consistent drying rate throughout the kiln.  The moisture laden air is removed from the kiln by way of an automatic ventilation system and large dehumidifiers.  The drying rate of the timbers is carefully monitored because the outside perimeters of the cants naturally tend to dry faster than the centers.  Uncorrected, this imbalance would cause severe checking (cracking), so the final stage of kiln-drying large timbers requires a steaming process.  This adds moisture to the outside portions equalizing the moisture throughout the wood.

As mentioned earlier, kiln-drying lumber is a science.  It is not a random act of loading material in a kiln, flicking a switch, and coming back at some later time to retrieve it when a timer rings.  It is a carefully monitored procedure.  Before the lumber is placed in the kiln, a kiln schedule must be prepared.  This schedule will outline the different sets of conditions to be carefully followed in order to achieve the desired moisture content, without damaging the wood.  The kiln operator will modify the conditions in stages based on the moisture content of the lumber or by time-intervals.  Sample logs in the kiln are connected to sensitive measuring devices outside the kiln chamber, and monitored for temperature and moisture content. Once it has been determined that the desired moisture content (15%) has been achieved, cross-section samples are  taken from the center of randomly selected cants in the kiln, and tested.

Moisture content of the timbers can be measured in a variety of ways, however, the most accurate method is by use of the "oven-dry-ratio" analysis.  This is done by first weighing the kiln-dried sample on a set of sensitive gram scales, then drying them down completely in a small oven. The ratio between the original kiln-dried weight and the final oven-dried weight represents the moisture content of the timber, inside and out. Another device used to measure moisture is the moisture probe, which measures only the outer fractional portion of the timber.  It cannot penetrate the wood deep enough to give an accurate reading of the moisture content throughout the log, but only the outer portion, which will tend to be the driest portion of the timber.