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How Growth Rings Affect the Strength of Timber

Whether you are planning a personal or commercial project, it is critical that you choose the appropriate wood type. However, wood type alone does not indicate whether timber is ideal for your intended use case. 

If you want to ensure that your project exhibits superior longevity and functionality, you will also need to consider the number of tree growth rings that the product features. 

As you are probably well aware, growth rings provide information about a tree’s age. What you may not know is that growth rings can also indicate how strong and durable timber is. 

By understanding how tree growth rings are formed and what they reveal about the strength of timber, you will be better prepared when purchasing lumber for your projects.

How Are Tree Growth Rings Formed?

tree growth rings

The vast majority of trees, including popular sources of timber like Douglas Firs, have growing points that are located beneath their bark. This growing point is known as the meristem. Throughout the year, the meristem will generate new cells, which form the growth rings.

During the more favorable parts of the year, a tree’s growth rings will be less dense and lighter in color because the meristem is creating new cells very quickly. As the favorable growing conditions give way to drought or other less desirable environmental circumstances, the growth ring will become dense and darker.

Timber Milling and Growth Rings

vertical vs flat grain

There are two primary timber milling options related to growth rings for processing trees. These options are flat grain milling and vertical grain milling. 

Vertical grain timber is produced by milling wood in a manner that positions the rings “vertically” in relation to the board’s face. Conversely, flat grain boards run parallel to growth rings. 

This vertical grain timber is more difficult to produce because the logs must be quite large. Vertical grain timber is primarily used for applications where the aesthetics of the wood are a concern. Modern vertical grain timber also exhibits better durability, making it perfect for crafting doors, boats, and the like.

Conversely, flat grain or mixed grain timber are great options when aesthetics are not a concern, such as when building frames. Mixed grain timber includes both flat grain and vertical grain boards. 

Ordering mixed grain lots gives builders more flexibility when they’re planning projects, as they can use the vertical grain boards for key joints and install flat grain boards in lower-stress sections of the structure.

Understanding Growth Ring Density and Direction

The three factors you should consider when purchasing timber are growth ring density, grain direction, and whether the wood is “clear” (knot-free). For most projects, ordering mixed grain timber is the most pragmatic. This approach gives you the best combination of durability, quality, and cost-effectiveness. 

If your project calls for knot-free boards, make sure to request clear timber. Also, if you are ordering structural timber like Douglas Fir, you should find out how many growth rings per inch the boards feature. 

Generally, you need boards with eight growth rings per inch or more, as this is considered dense structural timber. Growth ring density is not a concern when purchasing softer woods like Red Cedar or White Pine.

Reliance Timber’s Product Offerings

When sourcing timber for your project, it is critical that you are mindful of tree growth rings. Timber without adequate growth rings or a proper grain may not possess the durability necessary for your intended application. 

Additionally, it is vital that you specify whether you need clear or knot-free timber. For example, clear Douglas Fir would be suitable for building doors, boats, and other items where aesthetics and strength are of equal importance. Conversely, knotted Douglas Fir may not be suitable for these applications. 

If you need a reliable timber provider to source the materials for your projects, Reliance Timber can help. We provide top-quality mixed grain timber, including White Pine, Red Cedar, and of course, Douglas Fir. Our Douglas Fir selection includes dense structural timber that features at least eight growth rings per inch.

To learn more about our products, contact Reliance Timber today. We can assist you in selecting the best wood type for your project and get your materials delivered in short order.