Western Redcedar — Density, Movement, Workability & Cost

Of every species in the USDA Forest Products Laboratory's Table 4-3, western redcedar (Thuja plicata) has the lowest total volumetric shrinkage on record — 6.8%, lower than teak's 7% despite teak's reputation as the most dimensionally stable outdoor wood most people can name. It's a genuinely different kind of stability than teak's, though: western redcedar backs it up with a tangential:radial ratio of 2.1, meaning it moves unevenly between grain directions even while barely moving in total. It is simultaneously one of the most stable woods on this site and, by this site's own 2.0 threshold, technically movement-prone — both descriptions are accurate depending on which number you're asking about.

Light, brittle, and the reason siding and decking love it anyway

At 23 lb/ft³ and only 350 lbf, western redcedar is one of the lightest and softest species this site covers, which is part of why it's so easy to install as siding and decking — a person can carry a stack of it without fatigue. The tradeoff is real brittleness: screws pull through it more readily than through a denser softwood, edges crumble under impact, and its straight, splintery grain buries slivers deeper and more painfully than most woods. Pre-drilling matters here almost as much as it does on a dense hardwood like ipe, just for the opposite mechanical reason — not because the wood resists the fastener, but because it won't hold one driven without a pilot hole.

Working out the movement number at a siding-board scale

A 6"-wide bevel siding board moving from a wet 15% moisture content down to a seasoned 9% MC — a realistic outdoor swing — contracts about 0.060" (1.5mm) across its width, computed from this species' own 5% tangential shrinkage figure. That's a genuinely small number even by this site's standards, which is exactly why western redcedar siding and shakes stay tight and gap-free for decades when properly installed, despite the technically-elevated 2.1 ratio. Run your own board width on the wood movement calculator. An 8-foot bevel siding board at 5/8" x 6" weighs about 4.8 lb — check other dimensions on the wood weight calculator.

Gluing, finishing, and a fastener detail specific to this wood

Gluing is acceptable, though the wood's natural extractives can interfere with a bond and a genuinely fresh, unglazed surface matters more here than on a less oily softwood. Those same extractives bleed through light-coloured paint unless a proper stain-blocking primer is used first — an unprimed white-painted cedar fence will show tannin staining within a season. Left bare, it silvers evenly and attractively, which is why so much cedar siding and outdoor furniture is never painted or stained at all. One detail specific to this species: its extractives actively corrode plain steel fasteners, so stainless steel or hot-dip galvanised screws and nails are a real requirement, not a nice-to-have, on anything expected to last.

Durability that comes from actual chemistry, and a serious occupational hazard

Rated very durable, and unlike many "durable" claims that rest mostly on density, western redcedar's rot resistance comes from thujaplicin extractives that are genuinely fungicidal — sapwood, which contains almost none of them, has essentially no decay resistance by comparison, so sorting sapwood out of an exterior project matters. The same extractives carry a serious downside: western redcedar dust is one of the best-documented causes of occupational asthma in the entire wood trades literature, with plicatic acid producing genuine, sometimes persistent sensitisation in a meaningful fraction of sawmill and shop workers over repeated exposure. Dust extraction at the source and real respiratory protection are not optional recommendations here.

Cost and where western redcedar's durability pays off

At around $8 per board foot, western redcedar costs more than Douglas-fir but less than most true exotics, and buyers are generally paying for the durability-without-chemical-treatment story rather than for strength, since it's one of the weaker structural softwoods on this site. Decking and siding, shingles and shakes, outdoor furniture, greenhouses and guitar soundboards are the five uses it shows up in most — the guitar application in particular trades on its light weight and stiffness-to-weight ratio rather than its rot resistance.

Questions specific to western redcedar

Is western redcedar actually a cedar, botanically? No — like several other "cedars" in North American lumber trade names, it's a member of the cypress family (Thuja, related to arborvitae) rather than a true Cedrus cedar; the name reflects the trade's use of "cedar" for a broad category of aromatic, durable, lightweight conifers rather than strict botany.

Do I need to treat or seal western redcedar before using it outdoors? No sealing is required for the wood to perform durably — its natural extractives do the decay-resistance work — though a finish is worth applying purely for colour retention, since bare cedar will silver within a year or two regardless of any coating decision.

Is the asthma risk really serious enough to worry about for occasional hobbyist use? Occasional exposure carries far lower risk than the repeated, high-volume exposure documented in sawmill workers, but the wood trades' own occupational health literature treats it as a genuine, not theoretical, hazard — a basic dust mask and reasonable ventilation are sensible even for a weekend project, and anyone developing new respiratory symptoms while working this species regularly should take that seriously.