By the SaunaKitsUK.co.uk — The UK's Home Sauna Buying Guide Team · Updated May 2026 · Independent, reader-supported

Best Wood for a Home Sauna Kit UK: Spruce, Hemlock, Thermowood or Cedar?

Choosing the right wood for your home sauna kit matters far more than many people realise. The timber you select determines how quickly the sauna heats, how long it lasts, whether you'll suffer allergic reactions, and ultimately whether you'll actually use the thing for years to come. Most UK sauna kits come with one of four options: spruce, hemlock, thermowood, or cedar. Each has genuine trade-offs worth understanding.

Why Wood Choice Actually Matters

The wood in your sauna does more than look nice. It insulates the heat, absorbs and releases moisture from your body without rotting, and—critically—shouldn't offgas chemicals or cause reactions when heated to 70–90°C. Cheap timber that works fine in a garden shed can become uncomfortable or even problematic in a sauna. Conversely, premium woods often cost significantly more without delivering proportional benefits for most users.

Spruce: The Budget Default

Spruce is the most common choice for budget and mid-range UK sauna kits, and there's a reason: it's genuinely decent and genuinely cheap. European spruce (Picea abies) is lightweight, easy to mill, and has reasonable thermal properties. It's less dense than cedar, so it heats up quickly and won't retain scorching heat in the wood itself—something to appreciate when you're sitting on bench panels.

The honest downsides: spruce is softer than cedar or hemlock, so it marks and dents more easily. It's prone to warping if moisture isn't managed well, though modern kit designs handle this reasonably. Allergic reactions are rare, but spruce resin can irritate sensitive airways in a small percentage of people, especially if the sauna is poorly ventilated. Durability inside a sauna is about 10–15 years with decent maintenance; exterior cladding lasts longer.

Spruce works well if you're budget-conscious, won't obsess over cosmetic wear, and have reliable ventilation. It's the sensible choice for a first sauna.

Hemlock: The Underrated Middle Ground

Eastern hemlock (Tsuga canadensis) appears in fewer UK kits than it deserves to. It's softer than cedar but denser and more stable than spruce. Hemlock has a fine, even grain that looks subtle and professional. Importantly, it has very low resin content—lower than spruce—so allergic reactions are exceptionally rare.

Thermally, hemlock behaves similarly to spruce: it won't store excessive heat in the wood and heats up briskly. It's more rot-resistant than spruce and holds up to 15–18 years of regular use inside a sauna. The catch is availability: fewer UK suppliers stock hemlock kits, and when they do, pricing sits between spruce and cedar. If you can source it, hemlock is quietly excellent value—you're paying a moderate premium for noticeably better durability and fewer allergy concerns than spruce.

Thermowood: The Engineered Workaround

Thermowood isn't a timber species—it's softwood (usually spruce or pine) heat-treated to 190–220°C under controlled humidity. The process essentially cures the wood, reducing moisture content and resin volatility. What you get is spruce's affordability with improved stability, lower allergenic potential, and genuine durability gains.

Thermowood darkens beautifully during treatment, giving it an aesthetic appeal spruce lacks. Inside a sauna, it's stable, won't offgas troublesome resin compounds, and resists warping. Lifespan is comparable to hemlock: 15–18 years with care. Cost-wise, thermowood sits between standard spruce and hemlock—you're paying for the treatment, not rarity.

The trade-off: thermowood is engineered, not "natural," which matters if that distinction appeals to you. Thermally, it behaves identically to untreated softwood. Thermowood is the pragmatic choice if you want durability and low-allergy properties without cedar's expense.

Cedar: The Premium Long-Term Bet

Western red cedar (Thuja plicata) is the premium sauna wood. It's naturally rot-resistant thanks to extractive compounds that deter decay. Density sits between hemlock and hardwoods, so it won't scorch skin and doesn't absorb excessive ambient heat. Cedar has a signature aroma—pleasant to most, though some find it medicinal or overpowering in a closed sauna.

Allergic reactions to cedar are rare, and most people report the wood smells therapeutic. The scent diminishes over time but persists for years. Inside a sauna, cedar lasts 20–25 years or longer; it's genuinely a one-off investment. The wood won't warp significantly, ages gracefully, and genuinely improves with use.

The obvious downside: cedar costs roughly 40–60% more than spruce, sometimes double. A cedar-lined sauna kit will cost £2,500–£4,000+ for an average domestic unit versus £1,200–£2,000 for spruce. That premium buys you reliability, longevity, and a superior sensory experience—but only if budget permits.

Which Wood Makes Sense For You?

Choose spruce if you're cost-conscious, want proven reliability, and have adequate ventilation. It's economical, and you won't regret it.

Choose hemlock if you can source it and want better durability than spruce without cedar's expense. It's the thoughtful middle option.

Choose thermowood if you like the idea of engineered improvement and want stability plus lower allergenic compounds. It's modern and practical.

Choose cedar if budget genuinely isn't a constraint and you value long-term durability, aesthetics, and the full sensory experience. You're genuinely investing, not purchasing.

The Reality

Most UK homes will get excellent value from a spruce or hemlock kit used consistently for a decade or more. Cedar justifies itself through longevity if you're a committed sauna user. Thermowood splits the difference sensibly. Whichever you choose, air your new sauna well before first use, maintain moisture balance, and don't overthink it. The best wood for your sauna is the one you'll actually use.