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Kiln-Dried Logs

You've picked the plans. You've interviewed the builders. Now you have to ask one more question - “Do we use kiln-dried or air-dried logs?”

What is the difference?

The laws of nature ultimately determine the equilibrium between the moisture level in the environment and the moisture content of the logs. In order to reach this balance, air-dried logs need to be stored for up to a year. Kiln-drying accelerates the process achieving optimum log moisture levels in a matter of weeks. While air-drying is less expensive, the homeowner also realizes several other important benefits from kiln-drying.

Kiln drying maintains stability and uniformity.

Kiln-dried logs are also more resistant to twisting and cracking because of the consistent drying rate. The variable moisture content in air-dried logs leads to increased shrinking, warping and cracking during and after construction. All logs shrink during construction due to compression and moisture adjustments, however, kiln drying maintains the dimensional stability of the log and keeps shrinkage to a minimum.

loader loads logs into kiln

Kiln drying identifies logs that will detract from the beauty of your home. Since the inner wood core remains hidden, diseased or unhealthy wood can go undetected prior to the kiln cycle. After exposure to high temperatures, these problems become evident. Trained inspectors cull severely cracked and checked logs from production ensuring they are not used in construction. However, core problems in air-dried logs may not be obvious until after your home is built, resulting in costly repairs.

Kiln-dried logs ease construction.

Removing up to 10,000 pounds of moisture from the materials needed to build the average size home has the side benefit of making the log lighter and easier to handle on the job site. Two people can usually set and place even the longest of logs - saving you time and money.

Since air-dried logs do not dry at the same rate, you are left guessing about moisture content. This variable can make air-dried logs heavier, requiring more effort to move and set them in place.

Kiln drying takes care of nuisances.

Many logs contain flora and fauna in the form of insects, pitch, mold and fungus. High kiln temperatures sterilize the wood, killing fungus and mold spores, insect eggs and larvae. Kiln drying also crystallizes the pitch so it doesn't ooze out of the log and cause stains when exposed to warm temperatures.

Air-dried products make no provision for these natural nuisances. Warmer temperatures encourage mold and fungus growth, awaken dormant insect eggs and larvae and cause sap to seep down the face of the log. The kiln eradicates these nuisances.

Kiln drying maximizes the life of your logs. Reduced moisture levels in kiln-dried logs allow homeowners to apply preservative stains and finishes immediately following construction. Because of the uniform dryness, preservatives penetrate deep into the wood fibers to provide immediate and long-lasting protection.

Preservative absorption of an air-dried log is dependent upon the variable moisture content and may require several applications before achieving adequate protection.

So, what happens in the kiln? Kiln drying controls air movement, temperature and humidity to produce a superior wood product. Logs, which ultimately become your siding or beams, are loaded into the kilns and heated to temperatures high enough to dry the inner core. Since the outside of the log dries faster than the inside, steam maintains the optimum moisture level of the log's outer layer, while the inner core continues to dry. This method allows the log to dry uniformly.

During the kiln cycle, inspectors conduct eleven moisture meter readings to ascertain the water content in the logs. When the moisture level reaches the predetermined level, the logs are removed. Careful, consistent moisture extraction preserves the quality and longevity of the wood.

So, is it worth the cost?

Yes! Kiln-dried logs provide a lighter, cleaner, high-quality product for your home construction that maintains its dimensional integrity for a lifetime. Kiln-dried products are also free from insect infestations, unsightly mold or fungus stains and sap seepage problems.

No matter which process you choose, all log structures must be built to accommodate some shrinkage, settling and compression. Whether building with seasoned, standing-dead, green, winter-cut, or kiln-dried logs, a knowledgeable builder must anticipate and allow for movement in response to atmospheric fluctuations.

Kiln-Dried Logs vs Air-Dried
Potential Problem Kiln-Dried Logs Air-Dried Logs
Weight Easier handling
Water is removed, which reduces weight for both shipping and handling on the work site. Kiln drying can remove up to 10,000 pounds of moisture from a typical log home prior to shipping! Once properly dried, even the longest logs can easily be handled by two people.
Much heavier, difficult to handle.
Shrinking & Twisting Uniform & stable
Kiln drying produces logs that are more uniform and dimensionally stable. Logs are preshrunk before milling and grading. This creates tight joints and level floors.
Gaps often develop between logs. Walls shrink, doors and windows can bind. Frequent caulking is often required.
Checking & Cracking Reduced checking
Careful drying minimizes checking. Logs prone to checking are detected before grading and construction, defective logs graded out.
Air-dried logs are prone to severe checking, which occurs after construction as logs dry in the home.
Grading Defective logs culled
Any warped or twisted logs graded out by trained inspectors.
No moisture standards or effective grading.
Mold & Insects No mold or insects
Kiln-drying kills mold, wood decay fungi, and insects, eggs or larvae, helping to alleviate serious problem later.
Logs are not sterilized. Air drying cannot kill any insects that may be present in your logs.
Pitch No seepage
Kiln-drying crystallizes the pitch so it does not seep to surface.
Sap seeps to surface, especially around knots.
Finishing Longer-lasting finish
Stains can be applied immediately following construction, and they absorb deeper and last longer.
Usually not applied until at least one year after construction. Less effective, allows for weather stain.