Timber is a fundamental building material, representing wood that has been processed and prepared specifically for use in construction and engineering projects. This natural resource is derived from the trunks of trees. Timber has been used for millennia, making it one of the oldest materials used by humans to build shelter and infrastructure. Its appeal lies in its favorable strength-to-weight ratio, workability, and natural aesthetic qualities.
Defining Timber vs. Lumber and Wood
The terms “wood,” “timber,” and “lumber” are often used interchangeably, but they possess distinct meanings based on the material’s stage of processing and geographical location. Wood is the general term, referring to the organic substance that makes up trees, serving as the raw material before any processing begins.
In North America (the United States and Canada), “timber” commonly refers to unprocessed wood, such as standing trees or felled logs. “Lumber” is the term used for wood that has been milled, sawn, and cut into standardized sizes, ready for residential construction. Conversely, in the United Kingdom, Australia, and many other Commonwealth nations, “timber” is the standard word for all processed, ready-to-use wood products.
A technical distinction, particularly in engineering contexts, relates to size and application. Structural engineering standards often define “timber” as a piece of wood measuring 114 millimeters by 114 millimeters (approximately 4.5 by 4.5 inches) or larger in its smaller dimension. Pieces smaller than this threshold are classified as lumber. This distinction emphasizes that timber implies a larger, heavy-duty structural element used for substantial framing, while lumber refers to smaller, dimensional pieces.
The Journey from Tree to Usable Timber
The production of usable timber begins in the forest with the selection and harvesting of specific tree species. Trees are broadly categorized into two types: softwoods, which come from coniferous trees like pine, spruce, and fir, and hardwoods, sourced from deciduous trees such as oak, maple, and mahogany. Softwoods are commonly used for general structural framing due to their faster growth rate and availability. Hardwoods are often chosen for applications requiring higher wear resistance and durability.
Once a tree is felled, the process of turning the raw log into structural timber involves several distinct steps. The harvested logs are first debarked to remove the outer layer. The debarked logs are then transported to a sawmill where they are strategically milled, or sawn, into rough planks and beams of various dimensions.
A crucial step following milling is seasoning, or curing, which involves reducing the wood’s internal moisture content. Wood fresh from the tree, often called “green” wood, contains a high percentage of water, which causes it to shrink, warp, and become unstable as it dries. Seasoning is typically achieved by stacking the wood with spacers to allow for air circulation or by placing it in climate-controlled kilns. Kiln drying rapidly lowers the moisture content, which significantly increases the timber’s strength, stability, and resistance to decay and insect infestation.
Primary Applications of Structural Timber
Structural timber is defined by its ability to support loads and provide foundational integrity to buildings. Its primary application is in heavy framing, often utilizing a post and beam construction method where large, load-bearing wooden members form the skeletal structure of a building. The strength of timber allows it to be used for long-span roof trusses, providing support for the roof system.
Timber is frequently used in specialized engineering projects, including the construction of pedestrian and vehicle bridges, as well as temporary structures like scaffolding and formwork for concrete pouring. The development of engineered wood products, such as glulam (glue-laminated timber) and cross-laminated timber (CLT), has expanded its use into multi-story and high-rise structures. Exposed timber frames and trusses contribute a natural warmth and unique architectural character to the interior design of a space.