Terminology: Lumber vs. Timber

You may have heard the terms lumber or timber used to describe wood construction materials, but perhaps you’ve wondered what the difference is. Well, outside of North America, it is perhaps less confusing because timber can refer to all wood building materials and the term lumber generally isn’t used. But here in Canada both terms are used and there are subtle differences between them.

If you consult Webster’s dictionary, lumber is

wooden boards or logs that have been sawed and cut for use

and timber is

wood suitable for building or for carpentry

Both terms can describe the same thing, but notice that the definition of timber makes no mention of sawing. In North America, it is common to use lumber to refer to the wood products that have come from the mill, while timber can refer to milled wood, unprocessed logs, or even standing trees prior to harvesting.

Logs before milling are often called timber.

After milling and cutting, wood is often referred to as lumber.

Seems simple enough? Well, it gets a little more confusing once you get into the technical definitions. The American Institute of Timber Construction had defined lumber as

a manufactured product derived from a log in a sawmill, or in a sawmill and planing mill, which, when rough, shall have been sawed, edged, and trimmed at least to the extent of showing saw marks in the wood on the four longitudinal surfaces of each piece for its overall length, and which has not been further manufactured other than by cross-cutting, ripping, resawing, joining crosswise and/or endwise in a flat plane, surfacing with or without end matching, and working.

According to the Canadian design standard for wood structures (CSA Standard O86-14: Engineering design in wood), timber is

a piece of lumber 114 mm or more in its smaller dimension

In other words, at least in the Canadian construction and engineering context, timber refers to pieces of wood that are 114 mm x 114 mm or larger. That’s 4-1/2” x 4-1/2” if you’re more familiar with US Customary units. So a typical 4x4 post (actual dimensions 89 mm x 89 mm [3-1/2” x 3-1/2”]) is lumber, but a typical 6x6 post (actual dimensions 140 mm x 140 mm [5-1/2” x 5-1/2”]) is timber.

But just in case that wasn’t enough to confuse you, there are engineered wood products that break the 114 mm rule. There are glued-laminated, cross-laminated, nail-laminated, and dowel-laminated wood products that all referred to as timber. These laminated wood products are manufactured by gluing (or nailing, or doweling, as the case may be) sawn wood boards together to make larger panels, beams, or posts. These products are usually more than 114 mm thick, but there are some exceptions. There are standard glulam beam sizes available in 80 mm width. Glulam is still referred to as timber even when it is less than 114 mm wide.

Another example of an engineered wood product breaking the 114 mm rule is Parallel Strand Lumber (PSL). PSL is made from strands of wood clipped from thin sheets called veneers. The strands are all oriented parallel to each other and then glued and pressed together to make a beam or post. PSL is available in 130 mm and 180 mm widths, but despite exceeding 114 mm the product is still Parallel Strand Lumber.

So to summarize, lumber is a general term that describes building materials made by processing wood into boards, planks, posts, beams, etc. The smaller cross-sectional dimension is usually less than 114 mm [4-1/2”]. Timber generally refers to pieces that are larger than 114 mm [4-1/2”] in the smaller dimension. However, there are some exceptions to the 114 mm rule when it comes to engineered wood products.

References

“lumber” (2014). Merriam-Webster.com. Retrieved September 30, 2014, from http://www.merriam-webster.com/dictionary/lumber

“timber” (2014). Merriam-Webster.com. Retrieved September 30, 2014, from http://www.merriam-webster.com/dictionary/timber

American Institute of Timber Construction (1972). AITC 101-72: Standard Definitions, Abbreviations, and References. American Institute of Timber Construction, Englewood, CO.

Canadian Standard Association (2014). CSA Standard O86-14: Engineering Design in Wood. Canadian Standards Association, Mississauga, ON.

Stark, N. M., Cai, Z., and Carll, C. G. (2010). Wood-Based Composite Materials: Panel Products, Glued-Laminated Timber, Structural Composite Lumber, and Wood-Nonwood Composite Materials in Wood Handbook: Wood as an Engineering Material. Forest Products Laboratory, Madison, WI.