Redwood
Also called: sequoia, european redwood
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"Redwood" is a name for two different trees, depending on which side of the Atlantic is using it. In North America it means the wood of the tall coastal softwood commonly called redwood, a close relative of the giant sequoia that grows further inland in California's Sierra Nevada; in the British and European timber trade, though, "redwood", or European redwood, is an everyday trade name for an entirely different, unrelated softwood, sold alongside a partner timber called European whitewood.
Two trees, one name
Brett (2005) and Porter (1999) both use the trade sense of the word, listing European redwood alongside European whitewood and other species. Porter (1999) also places European redwood among the species groups used in an older British system for grading structural timber by strength, distinct from any grading of the American tree. Anyone buying timber sold simply as redwood needs to know which trade is being used, since the two woods are not related.
The American tree
The USDA (2021) describes the giant sequoia, Sequoiadendron giganteum, as a close relative of redwood that is larger in volume but grows only in a limited part of California's Sierra Nevada, and notes that its wood is used commercially in only very limited quantities, unlike ordinary redwood. Typical old-growth redwood itself, the USDA (2021) records, is moderately lightweight, moderately strong and stiff, and moderately hard: a middling set of properties rather than an extreme one in any direction.
Appearance and identification
Porter (2004) describes redwood's heartwood, the older, harder wood at the centre of the trunk, as ranging from light cherry red to a dark reddish brown, with a sapwood, the younger outer wood, that is near white or pale yellow by contrast. Hoadley (1980) compares its surface directly against spruce, a related conifer sometimes mistaken for it: spruce has a lustrous, slightly shiny side-grain surface, where redwood by comparison looks dull. Under magnification the difference goes further. Hoadley (1990) notes that redwood's ray cells, the cells that run across the grain to carry material sideways through the trunk, appear roughly square when a tangential section is cut, a slice taken at a right angle to the rays; baldcypress shares this feature, but most other conifers in the same group show oval or elongated ray cells instead, which is one way the wood can be told apart under a microscope. Porter (2004) also advises wearing a powered respirator helmet when working redwood, grouping it with several other species that call for the same precaution.
Fire behaviour and scale
Redwood's resistance to fire has been studied directly: the USDA (2021) derived a piloted ignition temperature, the temperature at which the wood will catch fire given a spark or flame, of 365 degrees Celsius for redwood, a figure that held steady regardless of the heat flux applied, the thickness of the wood, its moisture content, which surface was exposed, or a thin reflective paint coating. The tree's size lends itself to large structural timbers: Seike (1970) records fifty-metre sequoia posts in the timber structure Canada built as its pavilion for EXPO '70.