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While a competitive log home market breeds great dividends for the consumer, it also creates some pitfalls to avoid. With heightened competition comes conflicting information as each company touts its competitive differences and advantages. No topic reflects such differences in opinion and theory more than simple, concise explanation of settlement that is supported by unbiased, credible sources.

Definition:

"Settling is the term that describes the loss of log wall height over time. The principal causes of settling are: 1) shrinkage of log diameter as logs dry to a an in-service condition (also known as equilibrium moisture content, or EMC), and 2) compression of wood fibers under the load od the building..."

- International Log Builders Association

Drying Methods
Companies employ primarily two methods of drying logs - air drying and kiln drying. Both methods, properly executed, can generate the same end result. One should not assume, however, that the drier the log, the less the settling. The moisture content of the wood at time of construction is more important than the drying method.

"Dry logs... may settle nearly as much as green logs. In part this is because of the nature of the definitions of dry and green - 19% MC is a dry log and 20% MC is a "green" log, but theses two logs will obviously differ very little in the amount they actually shrink in diameter as they approach EMC.

It must be assumed that log walls made of dry logs will settle. Further, it should be assumed that logs stored outside, not covered by a roof, are not at EMC, and will shrink. The amount of shrinkage depends upon the difference between the actual moisture content of the logs (as determined by a moisture meter, for example) and the final in-service EMC."

- International Log Builders Association

Dryness Measurements and EMC
Moisture content is measured with a moisture meter within 1" of the log surface. Even if the surface moisture content equals the equilibrium moisture content of the local climate, the center of the log will most likely be higher. In that case the log will continue to settle until the center of the log has reached EMC as well.

"Due to the large cross section of logs typically used in log structures, it is very difficult to guarantee specific moisture content throughout the piece. While the wood within 1" of the surface may have a reading of less than 20% with a moisture meter, the piece can be expected to have greater moisture content within it."

- "Preservation and Maintenance of Log Structures", Log Home Council

Logs are typically air dried or kiln dried. While each has it advantages and disadvantages, one method is not superior to the other. Both are different roads taken to the same destination. Typically, logs are not dried to reach EMC, especially since EMC varies from location to location. That means a very dry log could absorb local moisture and swell.

"Once of the more unfortunate yet common fallacies is that kiln-drying leaves wood irreversibly dry, and that once dried the wood somehow becomes dimensionally stable."

- "Understanding Wood", R. Bruce Hoadley

Wood Species
Settlement will vary by wood species. While hardwood may settle more initially, softwood can be more susceptible to swelling whenever relative humidity changes from season to season. Hardwoods are denser and are therefore less susceptible to absorbing water vapor and thus are more stable throughout the years.

Engineering for Settlement
How a building system anticipates settlement is more important than the dryness or drying method. Utilizing kiln drying or standing dead timber and not accounting for some amount of settling is a long-term mistake. Log walls that are not free to settle in height are bound to develop gaps between log rows which will be susceptible to air and water infiltration.

"I would much rather have a house made from logs with 30 or even 40 percent moisture content, that is designed and built with full recognition of that fact, than a house made from logs at 20 percent moisture content, designed and constructed in denial of any more shrinkage or settlement will take place."

- Log Homes Made Easy online, by Jim Cooper

The most important thing to remember is the amount of settlement is not important; engineering for the proper amount is. It does not matter if settling gaps are 1 inch or 4 inches since the gaps will be covered by trim and will eventually reduce themselves.

"Under many circumstances a 8'-0" high log wall will shrink 2" to 4". Therefore provisions for shrinkage, i.e. the "Drop Zone", shall be made in all aspects of assembly as well as materials that are adjacent or anchored to or otherwise affected by components. Some log walls will shrink less than or greater than the above mentioned range. Individual manufacturers shall specify their range. Areas of concern are as follows:

Assembly Operation

1. Fasteners
2. Windows and doors - including trim
3. Support Posts

Adjacent Components

1. Partitions
2. Chimney/fireplaces
3. Kitchen cabinets
4. Plumbing and vent pipe
5. Stairs
6. Electrical
7. HVAC"

- International Log Builders Association

Time
The settlement period varies with climate, but usually two complete heating/cooling cycles is all it takes for a log home to completely settle. During that time frame the house needs to receive periodic adjustments. This fact often times strikes fear in the hearts of the consumers, as they have visions of spending endless time and sweat adjusting their home.

Fear not! Many of the affected systems listed above require only conscientious engineering before and during construction rather than physical adjustments. Vertical posts are the only elements which must be "tuned." They are present in all houses with covered porches and/or second levels. One level houses with truss roofs and no porches would not require and adjustment.

Posts require adjustment no more than two to three times per year and will require only a couple hours of work each time. It will not require any more once the house is two to three years old. If it is not engineered for settlement, however, ongoing maintenance and structural problems can result.

All building systems require sensible engineering. In evaluating log home companies, make sure they have considered the above information in designing their systems. The best systems are those that are not only promised but proven.

Sources

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