Vancouver averages 240 rain days per year. Temperature swings from −5°C winter nights to 35°C summer afternoons. Persistent humidity, freeze-thaw cycles, and coastal air that carries salt even 20 km inland. The wood inside your outdoor sauna is exposed to all of it — every session, every night, for decades. Choosing the wrong species is not a cosmetic mistake; it is a structural one. Here is the complete breakdown of the three main options: Western Red Cedar, Western Hemlock, and Thermowood.
1. Why Wood Choice Is a Vancouver-Specific Decision
Most online sauna content is written for Finnish, Nordic, or dry-climate North American contexts. Vancouver is different. Metro Vancouver’s climate is wet-temperate, not dry-cold. That distinction changes everything about wood performance.
The core challenge: sauna wood must simultaneously withstand extreme heat (80–100°C interior temperatures), direct moisture from bathers, and external weathering from one of the wettest climates in Canada. Wood that performs excellently in a dry-climate sauna may rot, warp, or grow mould on a North Shore property where the exterior sees 2,000 mm of rainfall annually.
A wood that scores well on interior sauna performance but poorly on exterior durability is the wrong choice here. You need a species that handles both. Let’s look at each candidate.
2. Western Red Cedar — The Local Standard
Why Cedar Dominates in BC
Western Red Cedar is not popular in Pacific Northwest sauna builds by accident. It is the product of a specific evolutionary adaptation: cedar’s heartwood contains thujaplicins, a family of natural aromatic compounds that give it genuine biological resistance to the rot fungi and insects that thrive in wet-temperate climates. This is not a surface treatment that washes off — it is intrinsic to the wood’s cellular structure.
For outdoor sauna applications in Metro Vancouver, this translates to real durability advantages:
- Rot resistance without chemical treatment. Cedar heartwood is rated Decay Class 2 (Durable) by the Canadian Wood Council. In test scenarios with direct ground contact in wet BC climates, untreated cedar heartwood outlasts untreated hemlock by 15–20 years.
- Dimensional stability in wet-dry cycles. Cedar has one of the lowest shrinkage-to-density ratios of any North American softwood. When Vancouver summer droughts and rainy winters cycle the exterior moisture content by 15–20%, cedar moves less than almost any alternative.
- Low thermal conductivity. Cedar does not heat up and store heat the way denser woods do. This is critical for sauna benches and interior walls — you should never feel burning when you sit down. Cedar’s thermal properties make contact comfortable at sauna temperatures.
- The aroma. Cedar’s essential oils produce the characteristic sauna scent that is deeply tied to the experience for most users. This is not cosmetic — the compounds responsible are the same ones providing biological protection. The smell is a proxy for the wood’s health.
- Local sourcing. Western Red Cedar is milled commercially in BC. We source directly from regional mills, which means lower embodied carbon, better quality control, and faster supply than imported alternatives.
Cedar Limitations
Honesty matters here. Cedar is not flawless:
- Cost. Cedar is the most expensive of the three options at $8–$12/sq ft installed for interior tongue-and-groove. BC mill prices have risen with lumber demand. Budget hemlock or thermowood can be meaningfully cheaper per square foot.
- Knots and sapwood. Cedar grade varies significantly. Sapwood (the outer white rings) does not carry the natural oils of heartwood and will not perform comparably. Specify clear heartwood grades — this is where the durability data applies. Knotty grades are less expensive but structurally weaker in high-heat, high-moisture environments.
- Softness. Cedar is a relatively soft wood (Janka hardness ~350 lbf). It dents more easily than hemlock or thermowood and can show wear in high-traffic seating areas over years of use.
Our recommendation: Always specify clear heartwood grades for sauna applications in Metro Vancouver. “Cedar” is a broad category. The durability properties that make cedar excellent for outdoor builds are concentrated in heartwood. Specifying correctly costs more upfront and saves significantly over the lifespan of the structure.
3. Western Hemlock — The Budget Alternative
Where Hemlock Works Well
Western Hemlock is BC’s most commercially abundant softwood. It is genuinely excellent wood in the right applications:
- Interior sauna benches and walls — interior only. For interior applications where the wood is not directly exposed to weather, hemlock performs well. It is stable, smooth-grained, and takes heat well without burning.
- Cost efficiency. At $5–$8/sq ft versus $8–$12 for cedar, hemlock can reduce interior material costs by 30–40% on a build. For a budget-conscious project where interior finish is the primary concern, this matters.
- Consistent grain. Hemlock’s fine, straight grain produces a clean, contemporary aesthetic. Some clients specifically prefer its lighter, more uniform look to the reddish warmth of cedar.
- No tannin bleed. Fresh cedar can sometimes bleed tannins onto lighter-coloured towels in the first months of use. Hemlock does not have this characteristic.
Why We Do Not Use Hemlock for Exterior Applications in Vancouver
This is where the Vancouver climate creates a hard constraint. Hemlock is rated Decay Class 4–5 (Non-Durable to Perishable) by the Canadian Wood Council for exterior use. In wet conditions, untreated hemlock will show significant fungal attack within 3–5 years.
In a Vancouver outdoor sauna context, “exterior application” means more than just the structural framing you can see. It includes:
- Any wood within the wall assembly that sees moisture intrusion
- The underside of exterior benches (even “interior” benches near the door)
- Floor structures, particularly near drain points
- Any component in the change room or cold rinse area
Hemlock can be treated with exterior-grade penetrating oils or preservatives to extend its life. But these treatments require reapplication every 2–3 years, introduce ongoing maintenance overhead, and still will not match the natural durability of cedar heartwood over a 20+ year horizon.
Hemlock verdict for Vancouver: Acceptable for pure interior applications in a well-built, well-ventilated structure. Not appropriate for exterior framing, outdoor-exposed surfaces, or any application where Vancouver’s moisture will contact the wood directly without barrier protection.
Not Sure Which Wood Is Right for Your Build?
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Get a Free Material Consultation →4. Thermowood — The European Import
What Thermowood Actually Is
Thermowood is not a species — it is a process. Thermally modified timber is wood (typically Finnish spruce or pine) that has been heat-treated at 185–215°C in an oxygen-depleted steam environment. This high-heat process permanently alters the wood’s chemical structure:
- Hemicellulose degradation. The sugars that wood-decay fungi feed on are broken down. The result is a wood that decay organisms cannot consume effectively — genuine Class 1 (Very Durable) biological resistance achieved without any chemical impregnation.
- Dimensional stability. Thermowood absorbs and releases moisture at a rate 50–80% lower than untreated wood of the same species. In Vancouver’s wet-dry seasonal cycles, this means virtually zero warping, splitting, or gap formation.
- Reduced thermal conductivity. The treatment further lowers thermal conductivity compared to untreated spruce. On sauna benches, this translates to excellent comfort at high temperatures.
- Darker, consistent colour. Heat treatment turns the wood a rich chocolate-brown throughout. The colour is not a surface stain — it penetrates through the entire board. This provides a distinctive, premium appearance that many clients strongly prefer.
Thermowood Limitations in BC
Thermowood is not the automatic superior choice despite its strong performance metrics:
- Cost. At $12–$18/sq ft installed, thermowood is 50–100% more expensive than clear cedar. For a full sauna interior, this premium is significant.
- Supply chain. The BC market for thermowood is thin. Lead times of 4–6 weeks from European suppliers are common. On a project with a tight timeline, this is a real constraint.
- Brittleness. The thermal modification process reduces the wood’s impact resistance. Thermowood is more brittle than untreated wood and can crack if fasteners are driven too close to edges. Experienced installation is required — this is not a DIY-friendly material.
- No aroma. The thermal process eliminates the natural scent compounds in the wood. If the characteristic cedar or birch sauna aroma is part of your experience expectation, thermowood will not deliver it. Many clients add löyly (sauna essential oil) to their water bucket as a substitute.
- Limited local forestry connection. For clients who specifically want BC-sourced materials — whether for environmental reasons or to support local industry — thermowood’s European origin is a meaningful trade-off.
5. Head-to-Head Comparison: Cedar vs Hemlock vs Thermowood
This table compares all three options across the factors that matter for an outdoor sauna in Metro Vancouver:
| Factor | Western Red Cedar | Western Hemlock | Thermowood |
|---|---|---|---|
| Installed Cost (interior) | $8–$12 / sq ft | $5–$8 / sq ft | $12–$18 / sq ft |
| Outdoor Durability (Vancouver climate) | Excellent (natural oils) | Poor without treatment | Excellent (modified) |
| Expected Lifespan (outdoor) | 20–35+ years | 8–18 years (treated) | 25–40+ years |
| Maintenance Required | Minimal (3–5 yr cedar oil) | Regular (2–3 yr treatment) | Minimal (optional UV oil) |
| Dimensional Stability | Good | Moderate | Excellent |
| Thermal Comfort (benches) | Excellent | Good | Excellent |
| BC Availability | Excellent (local mills) | Excellent (abundant) | Limited (4–6 wk lead) |
| Natural Aroma | Yes (signature cedar) | Subtle | None (process eliminates it) |
| Heat Retention | Good | Moderate | Good |
| Chemical Treatment Required | No | Yes (exterior) | No |
| BC-Sourced Forestry | Yes | Yes | No (European import) |
The pattern: cedar and thermowood are the two serious options for a long-lived outdoor sauna in Vancouver’s climate. Hemlock has a place in pure interior applications on a tight budget. For anything exposed to BC weather, hemlock requires ongoing chemical treatment to compensate for its lack of natural durability — and even treated, it will not match the lifespan of the other two.
6. What Cedar & Steam Builds With (and Why)
Our Standard: Clear Heartwood Western Red Cedar
We build exclusively with Western Red Cedar heartwood for all sauna interiors and structural components. This is not a brand decision — it is the result of building outdoor saunas in Metro Vancouver specifically for 10+ years and watching how different materials perform over time.
The case for cedar in Vancouver is practical: it is naturally durable without requiring chemical treatment, it performs reliably through the wet-temperate climate cycles that BC imposes, it sources locally from BC mills (meaning we can control grade and quality), and over a 20–30 year build lifespan, its total cost of ownership is lower than hemlock (which requires ongoing treatment) and more accessible than thermowood (which carries a 50–100% premium).
We offer thermowood as an upgrade option for clients who specifically want the aesthetic (the dark chocolate tone is distinctive) or the premium dimensional stability. If you want the most dimensionally stable interior possible and budget is not the primary constraint, thermowood is a legitimate premium choice.
We do not use hemlock for any outdoor-exposed structural or interior component. We will occasionally spec hemlock for specific interior accessory pieces (towel benches, shelving) where it makes economic sense and moisture exposure is managed — but never as the primary wall or bench material on a Metro Vancouver outdoor build.
7. Maintaining Sauna Wood in Vancouver’s Climate
The best wood is only as good as its maintenance. Here is what each species needs to stay healthy in BC conditions:
Western Red Cedar: Low Maintenance, Not No Maintenance
- Year 1–3: Let the wood acclimatize. Interior surfaces do not need treatment during this period. The natural oils are active and the wood is performing as designed.
- Year 3–5 (interior): A single application of food-grade cedar oil or sauna-safe teak oil will restore the colour and enhance the natural aroma if it has begun to fade. This is optional, not mandatory.
- Year 2–3 (exterior surfaces): Exterior-exposed cedar — the sauna’s outer walls, roof overhangs, exterior decking — benefits from a penetrating exterior oil or semi-transparent stain. This preserves colour and extends the surface life. UV is the primary enemy of exterior cedar, not moisture.
- What to avoid: Film-forming finishes (polyurethane, varnish) that prevent the wood from breathing. These trap moisture and eventually peel. Always use penetrating products.
- Ventilation is critical: After each sauna session, leave the door ajar to allow moisture to escape. This one habit extends the life of any sauna wood species by years.
Western Hemlock: Regular Treatment Required
- Every 2 years: Exterior-exposed hemlock requires reapplication of penetrating oil or exterior wood preservative. Skipping this in Vancouver’s climate will result in visible grey weathering and eventual fungal attack within 5–7 years.
- Check annually: Look for grey discolouration, soft spots, or surface checking. Any of these on exterior hemlock means treatment is overdue.
- Interior hemlock: Low maintenance if properly ventilated. Treat with sauna oil every 3–5 years.
Thermowood: Minimal Maintenance, One Consideration
- Interior: No maintenance required for the structural wood. The thermal process makes it biologically stable. Occasional sauna oil application is optional cosmetic upkeep only.
- Exterior thermowood: The wood will naturally silver-grey from UV exposure over 2–3 years if untreated — similar to teak or ipe in outdoor applications. Many clients prefer this patina. If you want to maintain the chocolate-brown colour, an annual application of UV-protective oil will preserve it.
- Handle with care during installation: Thermowood’s brittleness means pre-drilling fastener holes is mandatory. Do not drive screws directly into thermowood without pilot holes — this will crack the wood. This is particularly important near edges and ends.
8. Frequently Asked Questions
Pine and spruce are common in Nordic sauna traditions, but they are poor choices for outdoor Vancouver builds. Both species have very low natural durability (Decay Class 4–5), meaning they will require aggressive chemical treatment to survive outdoor exposure in Metro Vancouver’s wet climate. They also have a tendency to ooze resin when exposed to high sauna temperatures — pine in particular produces sticky sap pockets at bench-level temperatures that can mark skin and towels. For an interior-only sauna in a well-protected structure with managed moisture, kiln-dried Nordic spruce can work. For a standalone outdoor sauna build in BC, stick to cedar, hemlock (interior only), or thermowood.
No — cedar grade variation is significant and matters enormously for outdoor performance. The key distinction is heartwood versus sapwood. Cedar heartwood (the darker, reddish interior of the log) contains the thujaplicin oils that provide natural rot resistance. Cedar sapwood (the lighter outer rings) does not carry these oils and will not perform comparably in wet conditions. For sauna applications in Metro Vancouver, always specify “clear heartwood” grades. Common grades like “Select Tight Knot” (STK) may contain sapwood and are not appropriate for exterior structural applications. The price difference between grades is real — it reflects genuine performance differences, not just aesthetics.
Sauna floors are a distinct challenge: they must handle foot traffic, direct water, and the highest moisture loads in the structure. Our standard recommendation for Metro Vancouver outdoor saunas is either (a) pre-cast concrete or poured concrete with a drain — the most durable and maintenance-free option; or (b) removable cedar duck boards that sit above a waterproofed subfloor and can be removed to dry completely between sessions. If you want a wood floor, use clear heartwood cedar and design it for complete drainage and ventilation. Any floor material that traps standing water in a Vancouver outdoor sauna will fail eventually, regardless of species.
Yes, materially. Western Red Cedar’s aroma comes from thujaplicins and other volatile aromatic compounds in the heartwood oils. This scent is not just pleasant — research suggests these compounds have mild anxiolytic (anti-anxiety) properties and contribute meaningfully to the wellness experience. The aroma is strongest in new cedar and naturally fades over years as the surface oils dissipate, though it can be renewed with cedar oil treatments. Hemlock has a faint, pleasant wood smell but nothing comparable. Thermowood has essentially no scent — the thermal process drives off the aromatic compounds. If the sauna aroma is important to your experience, cedar is the only species that delivers it naturally.
Still deciding? Our full FAQ page covers 15 common sauna questions, or contact us directly for a material recommendation specific to your build and budget. See our full cost guide for how wood choice affects total project pricing, and read our installation guide for how we handle wood selection and specification on each build.
For context on the full build decision, read our comparison of sauna vs hot tub ownership in Vancouver, our breakdown of complete sauna build costs for 2026, and our DIY sauna build guide if you’re considering tackling the build yourself.