Western red cedar for saunas: grades, aroma, durability and care

The short answer

• Western red cedar is our principal sauna timber. We use it for walls, ceilings and, in clear grades, benches and backrests in most of the saunas we build.
• It is among the lightest of the common sauna species, so it passes heat to your skin slowly, and it moves less with moisture than the other mainstream sauna timbers.
• Australian references rate its heartwood as durable and termite-resistant, which matters in Queensland, especially outdoors.
• The trade-offs are real: a strong scent that not everyone likes, a soft surface that dents, colour that varies from board to board, and a higher price for clear grades.
• Grade matters as much as species. Clear boards wherever skin touches; clear or knotty on walls and ceilings.

For how cedar fits among the other sauna timbers, start with our guide to choosing sauna timber.

What it is and where it comes from

Western red cedar is Thuja plicata, a softwood native to western North America, from British Columbia into the US Pacific Northwest. It is sold as western red cedar, “Canadian red cedar” or simply “Canadian cedar”. The common name causes confusion: it is not a true cedar (Cedrus), and it is unrelated to Australian red cedar (Toona ciliata), a mahogany-family tree. Specify it by its botanical name.

Appearance, colour and grain

The heartwood ranges from pinkish-brown to deep chocolate, often streaked, while the sapwood is pale. That variation is the timber’s character: no two boards match, and a cedar room reads as warm and layered rather than uniform. Clients who want an even, single-tone interior should know this before choosing it.

The grain is straight and the texture coarse. The timber is also very soft; the Queensland Government places it in the softest of its six hardness classes. That softness is part of why it feels comfortable, and the reason it marks.

Clear or knotty

Cedar is sold in appearance grades. The grade names used by Real Cedar, the Western Red Cedar Lumber Association, come from its siding grades:

No sauna-specific grading rule exists, and grade names vary between product lines, so the grade and the grading rules belong on every order.

Knots matter on benches for a physical reason. A study of Scots pine found that air-dry density rose by as much as 94% as the knot area in a section increased, and denser wood conducts heat faster. Cedar knots are not known for bleeding resin the way pine and spruce knots do, but they are still denser, so anything you sit or lean on should be clear. Knotty grades are a legitimate choice for walls and ceilings, giving a more traditional look at a lower cost.

Aroma

Cedar has a strong, sweet, long-lasting scent, and for many people it is the smell of a sauna. Others find it overpowering, particularly in a small room at full heat. If you are unsure, warm an offcut and spend some time with it before committing. People who prefer a near-neutral room usually do better with Canadian hemlock.

We make no health claims for the aroma. It is a matter of preference.

Resin and extractives

Cedar is not a resinous timber; Real Cedar describes it as naturally pitch- and resin-free. Its colour, scent and durability come from water-soluble extractives, including thujaplicins and plicatic acid. Those extractives have two practical consequences:

• Water can draw them to the surface, leaving tan or brown marks.
• They react with iron. Iron fixings stain cedar blue-black, and WoodSolutions warns that damp cedar is corrosive to iron and copper. Use stainless steel or another non-staining fixing throughout.

How it feels at sauna temperature

Every surface in a sauna heats towards the air temperature. Timber is comfortable because it passes that heat to your skin slowly, and the main factors are density and moisture: lighter, drier wood feels gentler.

Western red cedar is at the light end of the scale. Published figures vary between authorities:

The US Forest Products Laboratory gives its thermal conductivity as about 0.10 W/m·K at 12% moisture content, at the low end of its range for softwoods. In practice, a clear, well-dried cedar bench is among the most comfortable surfaces you can sit on in a hot room. “Cedar doesn’t absorb heat” is the common way of putting it, but it is inaccurate: the timber reaches room temperature like everything else, and simply delivers that heat slowly.

Stability and moisture movement

A sauna dries timber hard every session, then lets it take up moisture again. Boards that move a lot open joints, cup and check. Cedar has the lowest shrinkage of the mainstream sauna species, at 6.8% volumetric from green to oven-dry in the Forest Products Laboratory’s figures, against 12.4% for western hemlock and 11.5% for quaking aspen. Real-world movement is a fraction of those laboratory values, but the ranking holds: cedar stays flat and tight better than the alternatives, and resists warping and checking well.

Stability still depends on installation. Heating drives moisture out, so timber fixed too wet will open its joints after the first few heat-ups. Finlandia, a US sauna manufacturer, specifies wall and ceiling boards kiln-dried to no more than 11% moisture content. Boards should also acclimatise on site after the wet trades are finished, and be fixed to battens with an air gap behind.

Durability and termites

WoodSolutions and the Queensland Government both rate western red cedar heartwood:

• Above-ground durability: Class 2 on the Australian 1–4 scale (1 is most durable).
• In-ground durability: Class 3 (WoodSolutions) or Class 2 (Queensland). The sources differ, and sauna timber should never be in the ground anyway.
• Termites: resistant.
• Lyctid borers: not susceptible.

These ratings apply to heartwood only. Inside a well-ventilated hot room, decay resistance matters less than it sounds: decay needs timber far wetter than a sauna that dries out after use, and the US Forest Products Laboratory notes that decay essentially stops at about 38 °C. Durability counts most for outdoor sauna cladding and for any timber that stays damp.

Termites are a different matter. Queensland has both subterranean and drywood termites, and drywood termites don’t need ground contact. Cedar’s termite rating is a genuine advantage over hemlock and thermally modified timber, neither of which is rated resistant. It does not make a building termite-proof: management of the structure and subfloor is a design and certification matter.

Where it works in the room

• Walls and ceilings: clear or knotty. The ceiling is the hottest zone, and cedar’s low density suits it well.
• Benches, backrests and headrests: clear grade only. Finlandia and SAWO both use clear cedar for bench timber. Rounded edges reduce the chance of the grain lifting at corners.
• Outdoor saunas: cedar’s durability and termite rating make it a strong exterior cladding.
• Commercial rooms: cedar works, but its softness shows under heavy traffic. Plan removable, replaceable bench slats and robust concealed stainless fixings, carried by framing rather than by the lining.

Caring for western red cedar

Cedar needs little from its owner, but its softness and its water-soluble extractives shape how it should be cleaned. Our care guide sets out the whole-room routine; this section covers what is particular to cedar.

Everyday care and drying

• Sit on towels. Harvia asks for bench towels in every sauna, and on soft cedar they keep sweat and skin oils out of the surface where marks start.
• Wipe and dry after each session. Take out towels and the bucket, wipe water drops off the benches and dry the room. Harvia suggests leaving the heater on for about 10 minutes with the vent open and the door ajar. Why it matters: water sitting on cedar draws its extractives to the surface as tan or brown marks.
• Keep products off the timber. Harvia warns against smearing sauna scents, honey or other body-care products on the wood.

Cleaning with the grain

• Warm water and a mild, sauna-suitable cleaner. Harvia specifies slightly alkaline products (pH 8–10) and a thorough clean one to three times a year for a family sauna.
• A soft brush, sponge or cloth, along the grain. Cedar dents and scuffs easily, so scrub gently.
• Never steel wool or wire brushes. Real Cedar, the Western Red Cedar Lumber Association, warns that metal deposits react with cedar’s natural chemistry to leave blue-black stains.
• No bleach, chlorine, harsh cleaners, pressure washers or abrasive pads inside the sauna. LeisureCraft rules out bleach and harsh cleaners on its cedar saunas.
• Rinse lightly and dry thoroughly, with the heater on for a while and the room ventilated. Use a reasonable amount of water, not a soaking.

Colour change and ageing

Indoors, cedar darkens gradually with heat and light, and faster where steam hits. Benches mark first, where sweat, skin oils and water land. Harvia notes that sauna timber blackening over time is normal, and that sunlight, heater heat, wall treatments with poor heat resistance and fine particles from the stones can all speed it up. Outdoors, unprotected cedar weathers to silver-grey, which LeisureCraft describes as normal. A cedar room that has been used for some years should look lived-in rather than new, and most people prefer it that way.

Surface marks and light sanding

For stubborn marks, Harvia suggests a light sanding with fine sandpaper, always along the grain, followed by a clean and a full dry. Remove the sanding dust. Real Cedar’s guidance for exterior cedar mentions specialist cleaners for extractive and iron stains; inside a sauna, use only products the sauna or product maker approves for that use.

Treatments: optional, and sauna-specific only

• No varnish, lacquer, paint or ordinary stain inside the hot room. Harvia rules out lacquer; Finlandia rules out sealers, paint and varnish; and Tylö-Helo tells owners not to apply paint, stain or other finish coatings to interior wood.
• Walls and ceilings can be left untreated. Harvia says a family sauna’s walls need no treatment. If you want to make cleaning easier, use only a product made for sauna interiors. LeisureCraft says the interior cedar of its saunas is normally left natural.
• Benches can be treated if you choose, with a sauna bench oil or wax used exactly as its data sheet allows. Harvia recommends paraffin oil on benches one to three times a year, depending on use, applied to completely dry timber with the bench ends treated especially well. Tikkurila’s Supi Laudesuoja bench oil is applied, the sauna heated, and the surplus wiped off.
• Test first. Oil deepens the colour, so try it on the underside of a board.
• One system per surface. Tikkurila’s Supi Saunavaha sauna wax can go on benches and walls, but not over oiled timber unless the oil has almost completely worn away. Record what was used so later treatments match.
• Let it cure. Readiness depends on the product: Tikkurila says its bench oil is ready once absorbed into the wood, and its wax is ready for use after about 24 hours.

Bench care

Benches carry the wear in a cedar room. Keep them under towels, wipe them after each session, and clean and dry them as part of each thorough clean. Check them and their supports as part of each thorough clean: loose slats, raised fixings and splintered edges should be fixed before they are sat on. Clear-grade, removable slats make it easier to sand or replace a worn board.

If your room has infrared emitters, keep cleaners and treatments off them; see infrared and hybrid sauna care.

Advantages and disadvantages

Sourcing

Cedar is listed as Least Concern by the IUCN and is not CITES-listed. Real Cedar says more than 85% of British Columbia’s timberland is third-party certified, but that describes the region, not a particular shipment. Where certified timber matters to a project, ask for FSC or PEFC chain-of-custody documents for the specific order.

How cedar compares

If cedar’s scent or colour variation doesn’t suit, Canadian hemlock gives a paler, quieter room at the cost of more movement and no termite rating. Thermally modified timber is very stable and dark, but brittle, smoky-scented and not termite-resistant. The timber hub covers the remaining options.