The Builders who construct wooden frame structures take their time to choose the right kind of timber before starting construction. Several characteristics associated with the timber define the engineering time and pattern. Before building your customized home, you must know the parameters determining the structure's durability and finish.
Color, odor, specific gravity, moisture content, grain, shrinkage, and strength are the essential characteristics determining wood and timber properties. Typical color and odor characterize most trees. For example, dark brown wood color is typically found in walnuts, whereas golden yellow is the characteristic of teak wood, and the softwoods have a creamy white color. Pine trees can be spotted from afar because of their typical resinous smell. Another fundamental quality of timber is the characteristic of specific gravity.
Interestingly, the specific gravity of wood is always below 1. The hardwoods have a specific gravity from 0.7 to 0.9, whereas, in softwoods, the specific gravity is below 0.7. Among all types of timber, cork is the lightest wood, having a specific gravity of 0.3. Just like the above two properties, the moisture content is another characteristic of timber that affects the quality of timber to a great extent. In timber, we can find moisture as free moisture in cell cavities and walls. There are other factors too that determine the quality of wood for construction. Now that we have a brief of the timber properties, let me walk you through the six timber properties that are important during the timber selection before building wooden frames:
Moisture Content
Wood is a highly hygroscopic substance. If the wood is fully saturated with moisture in cell walls and cavities, moisture content can reach 200% percent. Generally, the moisture content lies between 30-50% in most cases. The moisture content level of timber is called "equilibrium moisture content." Moisture is a useless and harmful component for timber selected for use in any construction process. Therefore, it is necessary to reduce moisture in timber either by natural processes or artificial drying methods. For example, the air seasoned timber contains 12-16 percent moisture, whereas, in the kiln seasoned timber, the moisture content is brought down to 4 to 6 percent.
Grain
Grain is the arrangement and direction of growth of the wood elements ( tracheids, fibers, and vessels) in the wood. Grain is of 2 kinds: parallel to the trunk and oblique to the trunk, concerning the longitudinal direction of growth. In ordinary woods, the tracheids and vessels collectively known as fibers grow parallel to the length of the tree trunk. This type of structure is called "straight-grained." In this kind, the fibers are very tightly and closely packed, giving a fine-grained texture in the wood. In the other case, the fibers do not grow parallel to the trunk; instead, they are arranged in a twisted and spiral manner. It is the second kind of grain known as the "cross-grained."
Specific Gravity
Specific gravity is another essential property of woods that plays a vital role in determining the type of timber. Wood is a very light material, and so its specific gravity is always less than 1, just like water. However, it is interesting that if wood tissues are compacted enough not to leave any pores between them, the specific gravity will shoot up to 1.5, which is heavier than water. Such compression is, however, not possible by natural process. As a result, the specific gravity in woods varies greatly. Some timber may be as light as the specific gravity of 0.3, whereas others are heavy and have a specific gravity of 0.9. This depends on the structure and presence of pores in them. For example, the heartwood is heavier than the sapwood in the same tree.
Color and Odor
Most trees are typically characterized by their color and odor. For example, walnut wood is distinguished by its typical dark brown color, whereas a freshly cut teak has a golden yellow shade. Similarly, the softwoods like deodar and pine are of light cream color or white color. Some trees have such a strong odor that their smell can easily spot them if we talk of odor. Different trees have an unfamiliar smell associated with them; for example, we find an aromatic smell with the teak woods while the pines smell like resins. Know that the color and odor show significant variation in timber in different climates zones and topologies.
Strength
Various aspects of strength are considered while choosing the suitable timber for your framed structure. Density, moisture content, presence of defects, compressive strength, tensile strength, and transverse strength are the various aspects that collectively define the term "strength" in timber. Let's briefly know them one by one:
- Density: Higher is the density of the timber, greater will be the strength of the timber. The high density of timber results from thicker cell walls, and thick walls mean more amount of wood substance per unit volume.
- Moisture Content: We know that the higher the timber's moisture content, the lower the strength. It is because the element water has no load-bearing capacity. The increased volume of water in the cells decreases the volume of the wood tissue.
- Presence of Defects: There can be some natural and artificial defects in the timber, such as cross-grain, knots, shakes, etc. All of them decrease the strength and durability of timber.
- Compressive Strength: Timber from most trees are amazingly strong even under high compressive loads of 500kg/cm2 to 700kg/cm2.
- Tensile Strength: Wood has strong tensile forces parallel to grain but is fragile when these forces are made to work perpendicular to the grain.
- Transverse Strength: The primary reason for using timber to construct a beam is its high bending strength. The bending strength (transverse strength) of timber varies from 300 to 900km/cm2.
I hope now you have got an overview of timber properties and know what factors you should consider before building wood frames.