Redwood lumber, primarily from the species Sequoia sempervirens, is known for its unique reddish-brown color, often called “redwood brown.” This distinctive hue has established the wood as a prized building material. It is valued for its uniformity in color and texture, making it a popular choice for architectural applications where aesthetics and performance are important.
The Source of the Distinctive Color
The reddish-brown coloration is not a structural part of the wood fibers but comes from a high concentration of organic compounds known as extractives deposited within the heartwood. These extractives are complex polyphenolic compounds that act as natural pigments. They are synthesized by the tree as the inner, non-living sapwood transitions into the heartwood.
Specific coloring agents, such as the crystalline compounds sequoyin and isosequein, contribute significantly to the pigmentation. Variations in heartwood color, which range from light pinkish-brown to deep reddish-brown, relate directly to the quantity and type of these extractives present. This pigmentation is confined almost entirely to the heartwood, while the outer sapwood remains a much lighter, cream-colored hue.
Physical Properties and Structural Stability
The same extractives that give redwood its color also provide a natural defense mechanism, contributing to its structural longevity. These polyphenols are naturally toxic to many common wood-destroying organisms, lending the heartwood resistance to decay, rot, and insect attack. This inherent resistance means that redwood heartwood performs well in outdoor environments without the need for chemical preservatives.
The wood is also known for its dimensional stability, resisting warping, checking, and shrinking when exposed to changes in moisture and temperature. This characteristic is beneficial for exterior applications where lumber is subjected to environmental fluctuations. Its relatively low density also makes it lightweight and easy to handle during construction, while still maintaining sufficient strength for building projects.
Color Changes Due to Weathering
When redwood is left untreated and exposed to the elements, its characteristic brown color begins to change through a process called photodegradation. The ultraviolet (UV) radiation in sunlight breaks down the colored extractive compounds on the wood’s surface. This chemical degradation is initially noticeable as a subtle darkening of the wood.
As UV exposure continues, moisture interacts with the surface, and the color-bearing extractives are slowly bleached and leached away by rain. Over several years, this process leads the wood to develop a soft, silvery-gray patina, often described as a driftwood appearance. This color change is superficial and does not compromise the wood’s underlying resistance to decay or its structural integrity.
Common Architectural Uses
The combination of redwood’s appealing color and natural durability makes it a preferred material for exterior architectural applications. The highest-grade heartwood lumber is frequently chosen for exterior siding, where its stable nature helps maintain a clean and uniform appearance. Its resistance to moisture makes it well-suited for decks, fences, and garden structures.
Architects often specify redwood for projects requiring a natural, long-lasting material with minimal maintenance. The wood is also commonly used for outdoor furniture and specialty structures like pergolas and arbors. In all these applications, the wood’s deep color and ability to withstand environmental exposure are the primary factors driving its selection.