Western red cedar cladding: the premium timber weatherboard
Western red cedar (Thuja plicata) is a naturally durable, low-density premium cladding timber. Why it needs stainless or silicon-bronze fixings, and how it compares.
Ask Chalkline about this →Western red cedar (Thuja plicata) is a premium, naturally durable timber weatherboard cladding imported from North America. It is the high-end timber cladding choice in Australian architectural residential work: light, dimensionally stable, and naturally resistant to decay and insects without chemical treatment, at a price well above treated pine. Its one non-negotiable rule is the fixings, get the fasteners wrong and the facade stains within months.
What it is
Western red cedar is a softwood from the Pacific Northwest of North America. Its standout properties for cladding:
- Naturally durable. Cedar’s durability comes from natural compounds (thujaplicins and tannins) that resist rot, decay, and insect attack without preservative treatment. It is commonly rated as a moderately durable timber for above-ground use; durability classifications vary by source, so confirm the rating for your application rather than assuming.
- Low density and lightweight. It is one of the lighter commercial softwoods, which makes it easy to handle and fix.
- Dimensionally stable. It moves relatively little with moisture changes, so it stays straight and holds joints well as a weatherboard.
- Workable. It cuts, dresses, and takes a finish cleanly.
These are why it commands a premium: a naturally durable, stable, good-looking board that needs no treatment to last outdoors.
The fasteners: the rule you cannot break
The single most important thing a builder must get right with cedar is the fixings. Cedar’s natural extractives (tannins) react with iron and bare copper, and the reaction produces an ugly blue-black stain that bleeds down the board, often within months of install. The water-soluble polyphenols in the timber are the cause, and the most common source of iron is the fasteners.
So with western red cedar, use only corrosion-compatible fixings:
- Stainless steel (the usual choice),
- silicon bronze, or
- monel (a nickel-copper alloy).
Plain or uncoated steel and bare copper must not be used. Even galvanised fixings can be marginal where the coating is breached. The cost of stainless or silicon-bronze nails is trivial against the cost of a stained facade, and the staining is not a cleaning problem, it is a “the cladding looks ruined” problem. This is the defect that catches builders who treat cedar like any other weatherboard.
Installation
Cedar is installed as a lapped weatherboard (or in shiplap, board-and-batten, or shingle forms). The fundamentals:
- Lap the boards per the NCC weatherproofing provisions for external walls; a minimum lap applies, so set out the coursing to achieve it (verified 2026-05-25, ABCB NCC 2022 Housing Provisions). Confirm the current lap requirement for your edition and profile.
- Fix over a drained cavity where the climate zone or design calls for it (and increasingly required under NCC condensation provisions in cool zones).
- Pre-finish where possible. Coating or oiling the boards (including back-priming and end-sealing) before or soon after install protects the timber and evens out weathering. Left uncoated, cedar weathers to a silver-grey, which some designs want, but the move to grey is a finish decision to make deliberately, not by neglect.
- Seal cut ends and handle the boards to avoid surface marking; cedar is soft and dents more easily than a denser timber.
How it compares
| Western red cedar | Treated pine weatherboard | FC weatherboard (e.g. Scyon Linea) | |
|---|---|---|---|
| Material | Natural durable softwood | Pine, preservative-treated | Fibre cement composite |
| Durability | Natural (no treatment) | From the H-class treatment | Termite/rot/fire resistant |
| Fixings | Stainless / silicon bronze / monel only | Standard (per treatment) | Per manufacturer |
| Cost | Premium | Lower | Mid |
| Look | Natural timber grain | Painted timber | Painted, uniform |
| Maintenance | Oil/coat or let grey | Repaint | Repaint |
Against treated pine, cedar buys natural durability, stability, and the timber look, at a higher price and with the fixing constraint. Against an FC weatherboard, cedar is a natural material with grain rather than a painted composite, but it costs more and needs more finish care. The choice is usually driven by the architecture and the budget.
For a builder
- Specify the fixings in writing. Stainless, silicon bronze, or monel only. Put it on the order and brief the carpenter; this is the cedar mistake.
- Price it as a premium. Cedar is materially dearer than treated pine; make sure the quote reflects the board and the stainless fixings.
- Decide the finish early. Coat/oil for a maintained timber look, or let it grey deliberately; either way, back-prime and end-seal.
- Build the cavity. Treat cedar like any modern cladding: over a drained cavity where the climate zone requires, not direct-fixed in cool zones.
- Handle gently. It is soft and marks easily; protect boards on site.
Related
- Weatherboard cladding
- AS 5604: timber natural durability
- Treated pine
- Scyon Linea (FC weatherboard)
- Drained cavity
See also
Last updated: 2026-05-25. Verified: 2026-05-25. Quarterly review for currency.