Redwood Shrinkage: How Much Does It Shrink?

Redwood, known for its towering height and remarkable longevity, is a popular choice for both construction and landscaping. However, like all woods, redwood does shrink over time, which can impact its dimensions and performance. If you're considering redwood for your next project, understanding its shrinkage properties is crucial. So, how much does redwood shrink?

Redwood's shrinkage is primarily influenced by its moisture content. When freshly cut, redwood contains a high level of moisture, typically around 120% to 190% of its oven-dry weight. As it dries, this moisture content reduces, causing the wood to shrink. The amount of shrinkage depends on the specific species of redwood and the initial moisture content.

Redwood Species and Shrinkage

Redwood is not a single species but a group of related trees. The two most common species used in construction are Coast Redwood (Sequoia sempervirens) and Giant Sequoia (Sequoiadendron giganteum). Both species exhibit similar shrinkage properties, but there are slight differences.

The shrinkage of redwood is typically measured in units of thousandths of an inch per inch of board thickness. According to the Wood Handbook, published by the U.S. Forest Service, the average shrinkage values for redwood are:

• Radial shrinkage: 3.5% to 4.5%
• Tangential shrinkage: 6.5% to 7.5%
• Volumetric shrinkage: 10% to 12%

Radial and Tangential Shrinkage

Radial shrinkage occurs across the growth rings of the tree, while tangential shrinkage occurs along the growth rings. Redwood exhibits higher tangential shrinkage, which can lead to warping and cupping if not properly managed.

To minimize the impact of shrinkage, it's essential to use redwood that has been properly dried and kiln-dried lumber for applications where dimensional stability is crucial. Also, consider the direction of the grain when planning your cuts.

Volumetric Shrinkage

Volumetric shrinkage is a combination of radial and tangential shrinkage. It's a more accurate representation of the overall dimensional change in redwood. The higher volumetric shrinkage of redwood compared to other woods is due to its high initial moisture content.

Understanding volumetric shrinkage is particularly important when designing structures or furniture that rely on precise dimensions, such as doors, windows, or cabinets.

Factors Affecting Redwood Shrinkage

Several factors can influence the amount of shrinkage in redwood. Understanding these factors can help you predict and manage shrinkage in your projects.

Moisture content is the most significant factor affecting redwood shrinkage. The higher the initial moisture content, the more the wood will shrink as it dries. Other factors include temperature, humidity, and the wood's density.

Temperature and Humidity

Higher temperatures and lower humidity levels accelerate the drying process, leading to increased shrinkage. Conversely, cooler temperatures and higher humidity levels slow down drying, reducing shrinkage. This is why it's essential to acclimate redwood to its intended environment before use.

For example, if you're using redwood in a dry, hot climate, it's crucial to allow the wood to dry slowly and evenly to minimize shrinkage. This can be achieved by stacking the lumber in a way that allows air to circulate around it and protecting it from direct sunlight.

Wood Density

Redwood is a relatively dense wood, with a specific gravity ranging from 0.45 to 0.55. Denser woods tend to shrink less than less dense woods because they have fewer voids to fill with air as they dry. However, redwood's high initial moisture content still makes it prone to significant shrinkage.

To minimize the impact of redwood's density on shrinkage, consider using thicker stock for applications where dimensional stability is crucial. This can help offset some of the shrinkage that occurs as the wood dries.

In the world of woodworking and construction, understanding the behavior of different woods is key to creating lasting, functional structures. Redwood's unique shrinkage properties are just one aspect of this complex puzzle. By understanding and managing redwood's shrinkage, you can harness its beauty and durability for generations to come.