Cedar vs Hemlock for Outdoor Saunas: An Honest Comparison From Someone Who’s Lived With Both
Good sauna and cold-plunge guidance around sweat Decks should sound like someone has actually installed and used the setup. Space, power, drainage, heat-up time, and routine all matter.
Last October, my brother Dave and I spent a Saturday afternoon in his backyard in Duluth wrestling 85-pound hemlock panels onto the frame of his new barrel sauna. “This thing weighs twice as much as yours,” he said, sweating through his hoodie in 40-degree air. He wasn’t wrong. My own cedar unit, which I’d assembled two years earlier in Portland, had gone up with noticeably less grunting. But standing inside Dave’s finished hemlock barrel a week later, 182 on the thermometer and the walls glowing that pale, even, knotless cream, I understood the appeal. It looked like a Scandinavian spa. Mine looks like a cabin.
Two years with cedar. One winter watching my brother’s hemlock. Here’s what I actually know, and what I’d tell a friend before they spend $4,000 to $8,000 on a backyard sauna.
The Quick Answer
Cedar is softer, lighter, more aromatic, and more naturally rot-resistant. It costs more, roughly 20 to 40 percent more than a comparable hemlock build.
Hemlock is denser, harder, less aromatic, less rot-resistant, and cheaper. It has a cleaner, more modern interior look.
Both work. The right pick depends on where you live, what you want to spend, and whether you care about that cedar smell (more on that later).
What Cedar Actually Does Well
Cedar is the default North American sauna wood, and the reputation isn’t just marketing momentum.
It fights rot on its own. Western red cedar contains thujaplicin, a naturally occurring fungicide. The wood pushes back against decay and insects without any coating or chemical treatment. If your sauna sits outside through rain, sleet, and Pacific Northwest drizzle, this is a material advantage.
It stays cool enough to sit on. Low density means the surface doesn’t bank heat the way a harder wood does. At 200 degrees, I sit on my cedar benches bare-skinned, no towel, no flinching. This sounds like a small thing until you try a sauna where the bench burns your thighs.
The aroma is genuine. When you fire up a cedar sauna, the volatile oils release and the air fills with that deep, woodsy, slightly sweet scent. It’s one of those things people describe poorly but recognize immediately. Not everyone loves it (a small percentage find the VOCs irritating to their sinuses), but most people walk in and say something like “oh, that’s nice.”
It weathers gracefully. Exterior cedar ages to a silver-gray over a few years. Inside, it deepens to a warm amber. Both look intentional.
Where Cedar Falls Short
Softness is a real liability. I dropped a stainless steel ladle on my bench, and there’s a dent I look at every session. Aggressive scrubbing leaves marks. The wood is kind to your skin and unkind to your mistakes.
The aroma fades. This surprised me. By year two, the cedar smell was noticeably weaker. You can sand the interior surface to expose fresh wood and the scent comes back for a while, but it’s not a permanent feature. Think of it as a two-year bonus, not a lifetime guarantee.
And then there’s cost. Western red cedar supply has tightened steadily. Prices keep climbing. A cedar barrel sauna that cost $5,500 three years ago might run $6,800 today.
Color variation is the last complaint. Cedar panels range from blonde to deep reddish-brown, sometimes on the same wall. Knots are common. If “rustic” isn’t what you’re after, this can feel unfinished.
The Case for Hemlock
Canadian hemlock has become the popular alternative, especially with brands marketing to a younger, design-conscious buyer. The pitch is “modern sauna aesthetics,” and for once the marketing isn’t lying.
Visually, it’s striking. Tight grain, minimal knots, consistent pale tone. Dave’s hemlock interior looks clean and contemporary in a way my cedar never will.
It’s tougher. Hemlock resists dents and scratches better. Bench tops hold up longer under the everyday friction of towels, water, fidgeting kids, dropped phones.
It’s cheaper. Hemlock is more available and less expensive. For budget-conscious buyers, this is sometimes the whole conversation.
It’s nearly scentless. For people who don’t want a strong wood aroma, or who have cedar sensitivities, hemlock’s neutrality is a feature.
Where Hemlock Gets Tricky
Here’s the thing about hemlock: it has no natural defense against moisture. Zero thujaplicin, zero fungicide. In an outdoor application, you’re relying entirely on the manufacturer’s kiln-drying and thermal modification process to protect the wood. Reputable brands do this well. Cheap brands cut corners. And from the outside of the box, you can’t always tell the difference.
Hemlock also gets hotter to the touch. Denser wood stores more thermal energy. In Dave’s sauna at 190 degrees, sitting without a towel is uncomfortable on the bench. Not scalding, but enough to make you reach for cotton.
Weight is a practical concern too. Those panels are heavy. Assembly takes more effort (and ideally a second pair of hands). Shipping costs are higher, though most brands fold that into the sticker price.
If you’re buying hemlock, the single most important question to ask is: “What’s your thermal modification process?” If the sales rep can’t answer that clearly, walk away.
Thermally Modified Spruce: The Option Nobody’s Talking About Enough
This is the dark horse. Thermally modified spruce gets heated to roughly 200 degrees Celsius in a low-oxygen kiln, which fundamentally changes the wood’s cellular structure. Rot resistance goes up dramatically. Dimensional stability improves. And it comes out lighter than hemlock with better moisture performance than untreated cedar.
European sauna builders have used this process for years. It’s only recently becoming common in North America.
Some brands now offer thermally modified spruce as their top-tier option, even above cedar. Sweat Decks has a spruce thermal option that’s worth investigating if you’re building in a cold, wet climate and want long-term durability without cedar pricing. It’s the best durability-per-dollar play I’ve seen.
Climate Is the Variable That Matters Most
This is where I think most buying guides get it wrong. They compare the woods in isolation, as if every sauna sits in the same backyard. Climate changes everything.
Hot and dry (Arizona, inland California). Cedar or hemlock both perform well. Rot isn’t your enemy. Pick based on aesthetics and budget.
Cold and dry (Colorado, Minnesota interior). Hemlock is perfectly fine here. So is thermally modified spruce. Cedar’s rot resistance is less critical when moisture isn’t constant.
Cold and wet (Pacific Northwest, coastal New England). Cedar’s natural fungicide is real insurance. Hemlock works if, and only if, the brand did proper thermal modification. Skimp on that, and you’re looking at premature rot in three to five years.
Hot and humid (Florida, coastal Georgia, Gulf states). I’d pick cedar. Mold pressure is relentless in these climates, and cedar’s natural oils provide a meaningful buffer. Hemlock without excellent sealing is a risk.
Quick Notes on Other Woods
Aspen and basswood occasionally show up as bench-top materials. Both are extremely low-density and stay cool at high temperatures. Neither is structural enough for an outdoor sauna’s shell, but some premium builds use aspen bench tops on a cedar or spruce frame. If you sauna daily, the comfort upgrade is noticeable and, in my opinion, worth the upcharge.
Pine and fir appear in budget saunas. Avoid them. Pine bleeds resin at sauna temperatures, leaving sticky drips on your skin (and a smell that’s less “forest” and more “turpentine”). Fir warps. Neither belongs in this conversation.
Maintenance: What You’re Actually Signing Up For
Cedar. Light sanding every two to three years refreshes the aroma and cleans up discoloration. No interior finish required. If you want to preserve the warm exterior tone rather than letting it silver, an oil-based wood treatment once a year does the job.
Hemlock. Less interior maintenance because the harder surface doesn’t show wear as quickly. But the exterior absolutely needs annual sealing or wood treatment. Without it, moisture gets in, and without natural fungicide to fight it, the wood degrades faster.
Thermally modified spruce. Minimal interior work. The thermal treatment handles most of the moisture risk. Exterior treatment every two to three years is sufficient.
The Smell Question (Because Everyone Asks)
Cedar wins, full stop. Walk into a hot cedar sauna and the scent hits immediately. It’s one of those sensory details that makes the whole experience feel more… intentional. Like drinking whiskey from a proper glass instead of a plastic cup.
Hemlock barely smells like anything. Spruce has a faint resinous note that fades within weeks.
The workaround is simple: essential oils on the heater stones. A few drops of eucalyptus or birch on hot rocks will fill any sauna with steam and scent, regardless of what wood is on the walls. So if you love hemlock’s look but miss cedar’s aroma, the problem is solvable for about $12 a bottle.
Five Questions to Ask Before You Buy
- Where does the wood come from? A reputable brand knows its supply chain.
- Is it kiln-dried, and to what moisture content? You want 8 to 12 percent.
- Is it thermally modified? Critical for hemlock and spruce. Less so for cedar, but still a quality marker.
- What wood is used for the benches specifically? Some brands use a different (better) wood for seating surfaces than for walls. This is often a sign of thoughtful engineering, not cost-cutting.
- What’s the warranty against rot, warping, and dimensional instability?
What I’d Buy Today
If I were starting over in Portland with cedar pricing what it is, I’d seriously consider thermally modified spruce. Best durability for the money, low maintenance, and it performs beautifully in wet climates.
If I lived somewhere humid and had the budget, cedar. The natural rot resistance is too useful to ignore.
If I wanted a clean, modern interior look on a tighter budget, hemlock from a brand I’d vetted on thermal treatment process.
And if I’m honest? I don’t regret my cedar. Two years in, the aroma is fading, but the wood is aging beautifully and I haven’t treated the exterior once. In Portland rain, that’s saying something.
Don’t let glossy product photos make this decision for you. Ask about specifications. Touch the wood if you can. And think about your climate first, because it matters more than any brand wants to admit.
Frequently Asked Questions
Is cedar or hemlock better for an outdoor sauna? It depends on your climate. Cedar has natural rot and insect resistance that makes it better suited for wet or humid environments. Hemlock works well in drier climates, especially when properly thermally modified, and costs significantly less.
Does cedar smell go away in a sauna? Yes, gradually. The aromatic oils that give cedar its distinctive scent weaken noticeably after two to three years of regular use. Sanding the surface exposes fresh wood and temporarily restores the aroma.
Is hemlock safe for saunas? Yes. Canadian hemlock is widely used in both indoor and outdoor saunas. It’s hypoallergenic, virtually scentless, and durable. For outdoor use, make sure the hemlock has been kiln-dried and thermally modified to resist moisture damage.
What is thermally modified wood for saunas? Thermally modified wood has been heated to approximately 200 degrees Celsius in a low-oxygen kiln. This process alters the wood’s cellular structure, dramatically improving rot resistance and dimensional stability without chemicals.
Can I use pine for an outdoor sauna? It’s not recommended. Pine releases resin (sap) at sauna temperatures, which can drip onto skin and create an unpleasant smell. It also lacks the rot resistance and thermal stability of cedar, hemlock, or thermally modified spruce.
How long does an outdoor cedar sauna last? With basic maintenance, a quality cedar outdoor sauna can last 15 to 25 years or more. The natural oils in western red cedar provide significant protection against decay, even in challenging climates.
Do I need to seal or stain the inside of a sauna? No. Interior sauna wood should remain unfinished. Sealants, stains, and varnishes can off-gas at high temperatures and create health concerns. Exterior surfaces benefit from periodic oil-based wood treatment to slow weathering.