Dimension lumber is softwood lumber that is nominally 2 inches thick and of various lengths and widths. It is the structural softwood lumber used in most wood-based housing construction (2x4 platform-frame construction) in North America. Some engineered wood products, such as laminated veneer lumber, can be used in place of larger dimension lumber pieces.
Dimension lumber is produced in various widths (in nominal increments of 2 inches) and various lengths (in increments of 2 feet). The actual cross-sectional dimensions are less than the nominal dimensions, because the wood shrinks as it is dried and it is planed in its final production step. A “two-by-four” is therefore actually 1.5 inches thick and 3.5 inches wide in its finished form.
In Canada, most dimension lumber is produced from spruce-pine-fir (SPF). In the U.S., most dimension lumber is produced from southern yellow pine. Dimension lumber is usually graded on the basis of the quantity of natural characteristics present in each piece of wood (e.g., size and location of knots, slope of grain, checks, wane and warp) and any manufacturing defects. Dimension lumber is usually dried to a moisture content not exceeding 19%. Some dimension lumber is machine stress rated (MSR).
The U.S., Canada, Japan and China are the main markets for dimension lumber.
The largest market is in North America, where most dimension lumber (approximately 70%) is used in new residential construction or repair and remodelling of existing homes. Over 90% of North American detached or semi-detached new single-family houses are built with dimension lumber. The other two main uses are for non-residential construction, such as schools, libraries and low-rise office buildings, or for industrial purposes (i.e., to produce other products).
Canada has promoted North American platform-frame house construction (PFC) in Japan for over 50 years. More than 100,000 PFC homes are now built annually in Japan using imported dimension lumber. China now imports dimension lumber to make concrete forms for construction or for remanufacture into more finished products such as furniture and doors.
Production fluctuates between 45 and 75 billion board feet annually (106–177 million cubic metres), depending on the number of new housing starts and overall macroeconomic health. It is unlikely that North America can sustainably replicate its peak production, achieved in 2007, because of reduced harvesting in Western Canada (as a result of the mountain pine beetle epidemic), among other factors.
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