Material Grading - Density: Wednesday's Word(s) Of The Week

Another important physical characteristic of wood used in glulam is its density. Density is simply the mass per volume of wood, normalized to the moisture content. There is a strong correlation between wood's density and its strength: greater density = greater expected strength.

In many species, including Southern Pine and Douglas Fir, wood density can be judged by growth ring spacing. This is the actual visual grading we perform, sorting Dense (D), Medium (M) and Low/Course (C) lumber based on the growth rings.

Average density of southern pine has decreased as tree farms get more efficient at growing wood quickly. This resulted in a reduction of some southern pine lumber design values a few years ago, specifically the grades that did not evaluate density. Because glulam grading has always used density as a grading criteria, glulam design values were not affected…it is just more difficult to find large quantities of dense material.

*Wednesday's Word Of The Week is a feature on Unalam's Wood Times Blog. Each Wednesday our structural engineer, Rik Vandermeulen, will discuss a new term associated with glulam manufacturing. He will do this until we run out of words. If there is a timber or glulam term that you have heard of and want to know more about, let us know in the comments.