Log Home Insulation Saves Energy

Keep your log cabin warm and energy efficient with these tips on chinking, peeled logs, roofs and adding insulation.

| October/November 1991


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It may come as a surprise to some, especially owners, but many log houses should be insulated to make them energy efficient. A look at the R-values will tell one reason why. Dry wood can have an R-value of up to 1.25 per inch. Even low quality insulation has a value double that and more.

Another problem not often considered is moisture. Where does the moisture in the house go when the outside wall is solid wood? It still tries to get out, and might if there are cracks in the logs.

The propensity for moisture-laden air to move outside has been utilized in the past to make a log house better insulated. In the far north, where winter temperatures may stay below freezing for months, it was a common practice to seal the house from the inside. This was done by putting several containers of water on the stove and bringing them to a boil. The vapor traveled to the outside through the cracks. It immediately froze on contact with the outside air, effectively scaling the house until the outside air temperature again was above 32 degrees Fahrenheit. This cut down on drafts and made for a snug house, at least until the weather warmed up.

Logs have another property that helps explain why log houses don't seem to be as cold as their R-value would indicate: They are capable of storing heat. Logs in a house wall will absorb heat up to the temperature of the air in the house. When the house temperature is lowered — at night, for example — they give back heat into the rooms until the temperature is again equalized. Unlike a block or a stone wall, logs can be two temperatures simultaneously, one on either side.


Where basic insulation for a log house is needed, even if none is required elsewhere, is between the logs. No matter what type of log construction is used — round fitted, flattened, three-sided, or round with chinking — a thin layer of insulation should be put between each log and those above and below it. This fills irregularities between the logs and closes cracks open to the outside. Caulking or “chinking” is then done on either side of the insulation.

The size of the logs makes a difference. Many modern log houses are made of logs 8 inches or less in diameter. Two-sided and three-sided logs are often only 6 inches thick. When placed in a wall, there may be only 3 or 4 inches of contact surface between the logs. This contact is the thickness that should be considered when thinking of additional insulation. Not only is the joint between logs thinner than the logs, but that is the place where there will be leaks in the wall if any exist.

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