Wood Species

The primary wood used for the construction of log buildings is softwood.
Since ancient times, log structures have been built using pine (Pinus sylvestris), spruce (Picea abies), cedar (Cedrus), or Swiss stone pine (Pinus cembra). More rarely, larch (Larix) has been used. Saunas, on the other hand, were most commonly built from hardwood species such as linden (Tilia) or aspen (Populus tremula). In addition, standing deadwood of certain tree species can be distinguished as a separate category.
The quality and durability of the wood used in a log house—or any log building—depend on the wood species, the location where the tree grew and was harvested, and whether it was cut during winter or another season.
Therefore, we invite you to explore selected scientific data and professional insights to help you choose the most suitable wood for your dream home or any other log structure.
Log beams are prepared from the trunks of the tree species mentioned above. A tree trunk consists of bark (outer bark), inner bark (phloem), cambium, and the wood layer, which includes sapwood, heartwood, and the pith. The optimal annual ring width is: for Scots pine – 0.5–6 mm, for spruce – 0.5–7 mm, and for ash – more than 1 mm. Pine heartwood is clearly distinguishable in color from sapwood, unlike spruce or fir.

The color of wood depends on climatic conditions, the age of the tree, its growing environment, and the effects of time. Depending on where pine and spruce trees have grown—whether in mixed or dense forests, at the forest edge, on a hill, in wetlands, or in lowlands—their density and resin content can vary significantly.

Wood is not a homogeneous material. The heartwood is porous, highly sensitive to moisture, but retains heat well, while the sapwood is hydrophobic and less resistant to cold. One of the key properties of the main construction material used in log buildings (logs) is wood moisture content – the ratio of water (moisture) present in the wood to the mass of completely dry wood, expressed as a percentage (also referred to as wood moisture). Wood moisture depends on ambient air humidity and temperature. Wood stops drying or absorbing moisture once sorption equilibrium is reached. In a growing tree, moisture is distributed unevenly. In cross-section, the sapwood of softwood species contains 3–3.5 times more moisture than the heartwood. Along the height of the trunk, the highest moisture content is at the base, less in the middle section, and increases again toward the top.

The moisture content of freshly cut wood is 50–100%, wet wood 30–50%, damp wood 20–30%, air-dried 15–20%, and room-dry 8–12%.
In production, three terms are used to describe wood moisture: transport moisture (20–22%), service moisture (the moisture content of the wood product during use), and production moisture (usually 1–2% lower than service moisture). For building log structures, the recommended wood moisture content is 14–20%.
Moisture exits the heartwood through the ends of the logs. It is commonly believed that moisture leaves the sapwood faster than the heartwood. To accelerate moisture removal from the heartwood, a technological groove is made on the top of a wet log (beam), from one notch to the next. This longitudinal groove also reduces cracking and speeds up moisture release from the log core. As physics shows, liquid does not compress; changing compressive force does not reduce the amount of liquid or moisture. When moisture leaves the sapwood, it begins to shrink, while the heartwood, still containing moisture, resists compression, causing the sapwood to crack. The longitudinal groove helps equalize this effect.
An important factor is wood shrinkage. This refers to the free reduction of linear dimensions and volume as bound moisture leaves the wood. Shrinkage begins only after all free moisture has evaporated. It is not always visible and occurs only as hygroscopic moisture is lost, when the moisture content drops below 30%. Maximum shrinkage occurs tangentially, less radially, and minimally or almost invisibly longitudinally. For most of our wood species, the maximum shrinkage is: tangential 7–10%, radial 4–7%, longitudinal 0.1–0.3%, volumetric 11–17%.

Wood swells as it absorbs moisture from the air or when immersed in water. The result of this swelling process is an increase in dimensions, known as swelling.
Types of wood deformation include twisting, longitudinal, transverse, and edge deformation. In terms of resistance to deformation and reliability when using metal fasteners, spruce is comparable to pine.
Wood density is the ratio of the mass of the material to its volume (kg/m³ or g/cm³). It depends on the wood’s moisture content, species, growth conditions, position within the trunk, the forest’s geographic location, and heredity.

In any construction using wood—especially in log structures—a crucial factor for the quality of the building is which part of the tree is used for each stage of the work. An experiment was conducted with various types of sawn timber, the semi-finished products of which were buried halfway in the ground. Each year, the pieces were removed, examined, inspected, and the level of damage recorded. After an 8-year study, 14 wood species were classified into four groups. Durability was expressed using minimum indices, compared to linden sapwood. The results were as follows: the most durable heartwood was larch – 9.1, oak – 5.2, and ash heartwood – 4.9. Average durability was observed in European larch, spruce, and beech, as well as larch, spruce, and fir sapwood – ranging from 3.1 to 3.8 points. Low durability, from 2.0 to 2.5, was found in beech, oak, maple, and birch sapwood. The lowest durability index, from 1.0 to 1.8, was observed in the central part of birch, alder, mature pine, as well as alder, ash, and linden sapwood. When choosing a wood species for a log building, craftsmen in various countries, using scientific data, parameters, and many years of experience with different wood types, aim to answer the question: which wood is most suitable for producing and constructing such structures? In Lithuania, as is well known, most buildings are made from pine and spruce. The primary reason for using these species is their abundance in the region; other species are simply not available in sufficient quantities. 

So, which wood species is more suitable—pine, spruce, or perhaps cedar? Let’s explore different professional opinions, observations, and insights to answer this question for ourselves…
There are opinions that pine acts as a “donor,” while spruce is said to extract energy, meaning people living in houses built from spruce logs may feel that they have to give some of their energy to the walls. In contrast, pine shares energy, making occupants feel more comfortable in such a building. Another factor is that pine “sheds” less resin; although pine contains more resin, it is distributed more evenly throughout the log. Spruce, on the other hand, tends to have resin concentrated in so-called “resin pockets,” and as the wood dries, these pockets increase, causing significant resin leakage. It is often observed that some spruce buildings experience heavy resin runoff, even vertically along entire walls. The longer a spruce structure stands and dries, the more it “weeps.”
Pine is a medium-density wood and relatively heavy compared to other softwoods. Its mechanical properties are very good compared to spruce. As the width of the annual rings increases, density increases, while mechanical properties decline. Pine’s strength and low tendency to bend are also positive characteristics of this wood.

Pine is more susceptible to blue-staining fungi. Nowadays, there are many chemical treatments available to combat this fungus. However, there is also a traditional method for preventing blue stain: dissolve 1 kg of coarse salt, 500 g of soda, and 3–5 g of potassium permanganate in 10 liters of water. This solution is applied twice—once when the bark is removed and a second time when the log is prepared for assembly in the structure.

If we consider which wood species are best suited for different elements of a log building, the recommendations are as follows: Oak is ideal for window frames, sills, and posts, as it helps maintain log alignment and verticality. Spruce is most suitable for floor and ceiling beams, roof rafters, and other structural elements, as well as floors and ceilings. Spruce has a bending strength of 79.5 MPa, slightly less than pine at 86 MPa. It is less affected by temperature fluctuations than pine, making it a common choice for structural components. Pine, as mentioned earlier, “breathes” better due to superior air and moisture permeability and is more resistant to compression. Larch is often placed under the bottom log of a building due to its durability and higher resistance to decay. Linden and maple are used for carving and fine carpentry work.

Due to differences in cell structure, spruce absorbs less moisture than pine and shrinks less. Pine has more open cell structure, which allows better air and moisture permeability. For this reason, walls built from pine logs “breathe” best. If we consider thermal insulation, taking a natural pine log wall as 100%, the same wall made of spruce would be about 10% warmer, cedar 15–20% warmer, and larch 25–30% colder than pine.
It is said that pine is more resistant to atmospheric changes due to a higher proportion of heartwood and greater resin content. Pine also cracks less.
There is an opinion that the upper part of the log (sapwood) acts as protection, and damaging it supposedly reduces the wood/log’s durability—similar to peeled logs. You can judge for yourself if this is truly the case, as in a growing tree the sapwood facilitates moisture movement from the base to the top/canopy and the accumulation of active nutrients.

People often ask whether it is better to build a log house in winter or summer, and whether to use wood harvested in winter or summer. There are specific considerations. In winter, precipitation is less of a concern, and snow can be removed (unless it is wet snow). During transport, disassembly, and assembly, logs are less likely to get dirty. Regarding the wood itself, winter-harvested timber is more appealing because it is much drier—cold slows down sap movement in the trunk. Consequently, when the assembled structure dries, there is less shrinkage, fewer deformations, fewer cracks, and practically no fungal or wood-boring insect damage. Additionally, walls made from winter-cut logs are said to settle less. When it comes to Canadian or Siberian cedar, buildings made from these woods are warm and comfortable. They are popular in Europe and worldwide. Cedar homes perform well in harsh climates. Careful workmanship and the inherent properties of cedar have a huge impact on the overall quality and aesthetics of the building. The thermal insulation properties of red Canadian and Siberian cedar significantly surpass those of other softwoods due to the wood’s unique structure. It is proven that cedar’s essential oils positively affect the human body, improving respiratory, cardiovascular, and other organ functions. Cedar wood is also said to repel unwanted insects; historically, pests never infested cedar furniture. Modern studies confirm that cedar eliminates decay microbes indoors, keeping the air in such buildings almost sterile, which strengthens immunity and may help combat cancer. Cedar also has a very low compression coefficient and is practically resistant to longitudinal or transverse warping and cracking. Due to its low density and high air content within the wood structure, cedar experiences the least heat loss compared to other softwoods.

The key factors for a high-quality log house that can be used problem-free for many years are: selecting good-quality wood, ensuring the correct wood moisture content during construction, executing the work with proper technological methods, and using appropriate insulating materials. Only in such log buildings is the indoor microclimate exceptional—cool in summer and warm in winter.