Hemlock vs Spruce for Sauna: Which Wood Should You Choose?

Hemlock vs Spruce for Sauna: Which Wood Should You Choose?

Hemlock and spruce are two of the most commonly used softwoods in sauna construction. They're both affordable, widely available, and popular with manufacturers across North America and Europe. But they behave very differently in a sauna environment, especially when you factor in heat treatment.

Here's what you need to know before deciding which wood to go with.

Canadian Hemlock: The North American Favorite

Canadian hemlock (Tsuga canadensis) is one of the most popular sauna woods in North America. It's a tight-grained softwood that machines well, takes heat treatment beautifully, and has a neutral scent that doesn't overpower the sauna experience.

Raw hemlock is decent but not exceptional for saunas. It has moderate moisture resistance and can be prone to mold if not properly ventilated. That's why the vast majority of quality hemlock saunas use heat-treated (thermowood) hemlock. The thermowood process heats the wood to 400-430F in an oxygen-free kiln, which permanently changes the wood's cellular structure. The result is dramatically improved moisture resistance, mold resistance, and dimensional stability.

Heat-treated hemlock absorbs roughly 40-50% less moisture than untreated wood. It resists rot and mold not through volatile oils that eventually evaporate (like cedar does) but through permanent structural changes. The wood turns a rich chocolate-brown color and develops a subtle warm scent.

Nordic Spruce: The European Standard

Nordic spruce (Picea abies) is the default sauna wood across Scandinavia and much of Europe. Finland alone has more spruce saunas than any other type. It's a lightweight softwood with a fine, even grain and a clean, pale appearance.

Spruce is a good sauna wood in its natural state - it has low resin content compared to pine, reasonable moisture handling, and a mild scent. It's also light and easy to work with, which makes it popular with manufacturers.

Like hemlock, spruce benefits enormously from heat treatment. Thermowood spruce is common in European sauna construction and offers similar improvements in moisture resistance and dimensional stability. However, spruce is a softer wood than hemlock even after treatment, which means it dents and marks more easily.

Hemlock vs Spruce Sauna: Full Comparison

Durability in the Sauna Environment

Both woods perform well when heat-treated, but hemlock has a slight edge in overall durability. Its higher density means benches, floors, and high-contact surfaces resist denting and wear better over the years. In a sauna where you're sitting, leaning, and moving on the wood surfaces regularly, that hardness difference adds up.

Spruce's lighter weight is an advantage during assembly and transport but a slight disadvantage for long-term wear. Spruce benches will show marks and compression from regular use sooner than hemlock benches will. Both handle heat and moisture well after treatment, but hemlock gives you more margin for error.

Resin and Knots

Neither hemlock nor spruce is particularly resinous compared to pine, but spruce can have occasional resin pockets that weep at sauna temperatures. When resin heats up, it becomes sticky and can be uncomfortable if it's on a bench surface. Quality spruce sauna wood is graded to minimize knots and resin pockets, but it's something to watch for in cheaper spruce saunas.

Hemlock has very low resin content and rarely has this issue. It's one of the reasons it became the preferred sauna wood in North America.

The Verdict

Heat-treated Canadian hemlock is the better all-around choice for most sauna buyers in North America. It's harder, more durable, more widely available domestically, and has fewer resin concerns than spruce. The chocolate-brown color and neutral scent appeal to a wide range of tastes.

Nordic spruce is a perfectly good sauna wood, especially when heat-treated. If you're drawn to its lighter color, lighter weight, or the European tradition behind it, it'll serve you well. Just expect a bit more surface wear over the years compared to hemlock.

All SweatDecks saunas are built with FSC-certified, heat-treated Canadian hemlock. We chose it after extensive testing because it outperforms spruce on the metrics that matter most for long-term sauna use. Explore our outdoor sauna collection or barrel saunas to see the wood quality for yourself.

Frequently Asked Questions

Is untreated hemlock or spruce okay for a sauna?

Untreated versions of both woods can work for saunas, but they won't last as long or resist moisture and mold as well. Untreated hemlock handles sauna conditions better than untreated spruce, but neither comes close to the performance of heat-treated versions. If you're investing in a sauna meant to last 15-20 years, heat-treated wood is worth the modest price increase.

Does spruce smell stronger than hemlock in a sauna?

Spruce has a slightly more noticeable scent than hemlock when heated, but neither is strong. Both are considered neutral-scent sauna woods, especially compared to cedar or pine. If you're looking for a strong wood aroma, neither hemlock nor spruce will deliver that. They're better suited for people who prefer adding their own aromatherapy during sessions.

Which wood is better for barrel saunas specifically?

Hemlock is generally preferred for barrel saunas because its higher density and better dimensional stability help the staves maintain tight joints over time. Barrel saunas rely on precise stave alignment and band tension, so wood that swells and shrinks less (hemlock) creates a more reliable structure long-term. Spruce barrel saunas exist and work fine, but you may need to retighten the bands more frequently.

Can I mix hemlock and spruce in the same sauna?

You can, though it's uncommon. Some builders use hemlock for benches and high-wear surfaces and spruce for walls and ceiling where durability is less critical. The different wood tones can create an interesting visual contrast if done intentionally. Just make sure both are heat-treated if you go this route.