Redwood is a highly valued material in construction and woodworking, known for its distinctive reddish hue and remarkable durability. Its striking color and natural resistance to environmental factors make it a sought-after choice for outdoor applications like decking and siding. The wood is celebrated for its low density and workability. These unique characteristics stem directly from the biology of the tree, establishing its reputation as a distinctive building product.
Botanical Classification and Softwood Designation
The wood commonly referred to as “Redwood” originates primarily from the Coast Redwood, scientifically named Sequoia sempervirens. This species is a member of the Cupressaceae, or Cypress family, which places it firmly within the group of plants known as conifers or gymnosperms. The classification as a conifer is the biological reason why redwood is designated as a softwood.
The term “softwood” does not necessarily mean the wood is physically soft, but rather refers to the tree’s reproductive structure, which produces cones and needles. Unlike hardwoods, which come from flowering, broad-leafed trees, softwoods like redwood are characterized by their simple cellular structure, consisting mostly of tracheids. This biological distinction holds even though the wood possesses impressive properties that defy the common understanding of “softness”.
Wood harvested from Coast Redwood trees is generally categorized further into old-growth and second-growth material. Old-growth wood comes from trees that grew slowly under intense forest competition, yielding tighter grain and potentially better density. Second-growth redwood, while still a valuable material, typically grows faster and may display wider growth rings and more knots in early-life wood.
Unique Physical Properties of the Milled Wood
The most distinctive feature of milled redwood is its coloration, which is divided between the light-colored sapwood and the darker heartwood. Sapwood is the outer layer of the tree that transports water and nutrients, appearing almost white or very light in color. The heartwood, which is the older, inner core, is where the wood gets its characteristic shades, ranging from light reddish-brown to a deep, rich reddish-brown.
This rich color and the wood’s renowned durability are due to the presence of natural chemical compounds called extractives, specifically high concentrations of tannins. These extractives are deposited into the heartwood during the transition from sapwood, making the heartwood physiologically inert and resistant to decay. The concentration of these phenolic substances can be significant, sometimes accounting for 10 to 15 percent of the heartwood’s oven-dry weight.
The extractives provide the heartwood with a high degree of resistance to wood-destroying fungi and insects. Redwood also exhibits excellent dimensional stability, meaning it has a very low rate of shrinkage and swelling when exposed to changes in moisture. This property makes it less prone to warping or checking compared to many other wood species, which is highly desirable for applications exposed to the elements.
Clarifying Related “Redwood” Species
The term “Redwood” can cause confusion because it applies to three distinct species within the same subfamily of the Cypress family. The wood most often used for commercial lumber is the Coast Redwood, Sequoia sempervirens. This species is celebrated for being the world’s tallest tree and is the source of the durable, red-tinted wood.
A close relative is the Giant Sequoia, Sequoiadendron giganteum, which is the world’s most massive tree by volume. Although its wood is similar in appearance, it is generally considered more brittle and less suitable for commercial lumber applications than Coast Redwood. The Giant Sequoia grows in the Sierra Nevada mountains, geographically distinct from the coastal habitat of the Coast Redwood.
The third species is the Dawn Redwood, Metasequoia glyptostroboides, which was once thought to be extinct and is native to a remote region of China. Unlike its two relatives, the Dawn Redwood is deciduous, meaning it sheds its leaves annually. While it shares the “redwood” name and general family lineage, its wood is not typically found in the North American lumber market.