Today’s log houses are not only very elegant, but also energy-efficient. Kontio’s laminated logs and non-settling SmartLog™ logs have excellent breathability.

Breathability does not mean that the air can pass into or out of the building through the logs or the seams of the house. Modern log houses in fact have very little loss of energy. The logs breathe so as to balance out any fluctuations in air humidity inside the house.

“When the indoor air humidity increases, the logs absorb the additional moisture. And when the air becomes drier, moisture is drawn from the logs back into the room”, explains Kontio’s planning manager Mikko Löf.

Moisture does not pass all the way through the logs, however. They absorb excess air moisture only into the surface layers, to a depth of no more than about five centimetres. This is quickly released into the room air when the air humidity decreases.

Maintaining a balance

To illustrate the humidity-controlling properties of timber walls, Löf gives the example of a pleasant sauna evening with family or friends. As well as the moisture from the sauna, the shower is used several times both before and after the sauna. People sit chatting, enjoying the steam, throwing some more water on the stones from time to time. Time flies. Windows and mirrors soon steam up, and any papers in the dressing area start to wrinkle. These are signs that the air humidity level has increased to such a level that it condenses on cold surfaces.

It may be possible to improve the situation by turning up the air conditioning, which is the usual solution in light-structured houses. In Kontio log homes, however, this problem doesn’t even arise: the windows remain clear, and papers stay dry throughout the sauna evening. The air is not too moist or heavy–in log houses, it’s always easy to breathe.

“On the other hand, when the room air starts to become less humid in a log house, it doesn’t get too dry, as moisture gradually returns to the air from the logs,” Löf says.

Logs are therefore an effective buffer for maintaining air humidity at a comfortable level by increasing or decreasing it depending on the surrounding conditions. In winter, indoor air is often dry, but usually the amount of air humidity created through washing laundry and showering provides enough moisture for absorption into the logs. And when the air humidity is sinking too low for comfort, the logs begin to release some of the stored moisture back into the room.

This all happens quickly: the timber reacts to the fluctuations in humidity more or less in real time, many times a day. This complements the mechanical ventilation used in the building.

“Mechanical ventilation does not always function as optimally as it is designed to. For example, it can’t necessarily be quickly increased by just the right amount if the air humidity becomes high. And turning up the air conditioning increases energy consumption dramatically. In log houses, turning up the air conditioning is not always necessary, as the interior air quality remains good without it”, says Löf.

A healthy choice

The breathability of timber is beneficial in other ways as well, because stable air humidity is good for the health. Excessively dry air irritates the respiratory tract, and air that is too moist provides a breeding ground for bacteria. The ideal humidity level for indoor air is about 45 percent.

To maintain the good breathability of logs, surface treatment products must be chosen carefully. Breathable, organic paint or wax works are the best choices.

“Products that form an airtight film, such as varnishes, should be avoided”, Löf advises.

Feel the heat capacity in your hands

Not only does solid wood store moisture, but it also stores heat. Because log houses do not need to be heated or cooled as much as conventional, light-structured detached houses, they save energy. The specific heat capacity of timber reduces energy consumption in log houses by about 5 percent compared to conventional houses, and reduces the amount of energy needed for cooling by as much as 50 percent.

As well as saving money, using less energy is easier on the environment.

According to Löf, the heat-storing capacity of logs can even be felt by hand. The wall of a log building feels warm to the touch.

“By contrast, if you stand with your back to a stone wall or drywall, you can feel the cold on your back even at a distance of several centimetres. You can do the same test outdoors by sitting first on a rock and then on a wooden bench or tree stump. Everyone knows which one feels more comfortable!”

Kontio’s modern log houses are energy-efficient in other respects as well, as they are built according to Kontio’s own rigorous quality control requirements and also meet all the regulations that apply to airtightness. According to regulations, the air change rating must not exceed four–and the lower the figure, the more airtight the building is.

“All Kontio houses are tested for airtightness. This is part of the quality control for all our deliveries, even if the customer is building the house package themselves. The air change rating for Kontio log houses has even been as low as 0.2 in some cases”, Löf says.

Solid wood construction is a surer choice

When there is a good level of airtightness, energy is not wasted. It is also easier to maintain air quality when there is no uncontrolled leakage of air through the structures.

“Log buildings are comparable to other materials in terms of energy efficiency, and in some respects they are an even better and more reliable choice”, says Löf.

Structures with walls of solid timber are a good thing in this regard, Löf adds. A simple structure means fewer weak points where air leaks could occur in the wrong places.

“For example, in conventional structures hammering a nail or drilling into a thin wall board can cause a hole in the plastic moisture barrier behind the board. Solid wood walls have no such vulnerable barriers. And even if a nail or screw is removed later, there will be no leakage point left in the structure”.

Kontio designs its log houses with energy-efficiency in mind. This involves careful attention to factors such as the shaping of the recesses and holes to be made in the logs, and the seals of seams and corner joints. All solutions are subjected to lengthy testing in Kontio’s own product development lab and in external testing facilities prior to product launch. In addition, testing of finished log buildings provides a continuous flow of data for further development of products and solutions.

When properly constructed and processed, timber walls are energy-tight and help to balance out air humidity fluctuations. That’s why logs are a healthy, affordable and environmentally friendly, natural choice.