Can You Build a Sauna with Plywood? Pros, Cons, and Better Alternatives

If you're planning a DIY sauna build, plywood is probably already on your radar. It's cheap, widely available, and easy to work with — three qualities that make it the default material for just about every home construction project. So it's natural to wonder whether you can use it for a sauna too.

The short answer: plywood has a very limited role in sauna construction, and it should never be used as interior wall paneling, ceiling material, or bench surfaces in a hot room. The adhesives that hold plywood together release formaldehyde and other volatile organic compounds (VOCs) when heated, and a sauna is one of the worst possible environments for that kind of off-gassing. You're sitting in a small, enclosed, superheated space, breathing deeply with your pores wide open — the exact conditions that maximize your exposure to whatever the surrounding materials are emitting.

That said, plywood isn't completely off the table for every part of a sauna. It can serve as structural subflooring, exterior sheathing, or roof decking when properly sealed and separated from the heated interior. The key is understanding where plywood is acceptable, where it's dangerous, and what materials you should use instead for the surfaces that matter most.

Why Plywood Is Problematic in a Sauna Environment

To understand the issue with plywood, you need to understand what plywood actually is. Unlike solid lumber, plywood is an engineered wood product made by gluing thin layers (or "plies") of wood veneer together under pressure. The glue is the problem. Most standard plywood uses urea-formaldehyde or phenol-formaldehyde adhesives — chemical resins that off-gas at room temperature and off-gas dramatically faster when heated.

A traditional sauna operates between 150°F and 200°F. An infrared sauna typically runs between 120°F and 150°F. At these temperatures, the rate of VOC release from engineered wood products accelerates significantly. Formaldehyde, classified as a known human carcinogen by the National Toxicology Program, is the primary concern. But it's not the only one — plywood can also release acetaldehyde, toluene, and other volatile compounds that degrade air quality in an enclosed space.

This isn't a theoretical problem. Multiple sauna manufacturers explicitly avoid plywood in their construction for exactly this reason, using 100% solid wood throughout the cabin to eliminate any source of chemical off-gassing. If you're building or buying a sauna for health and wellness benefits — detoxification, cardiovascular support, stress relief — it defeats the purpose to fill the hot room with materials that add to your chemical exposure rather than reducing it.

Where Plywood Can Be Used Safely in a Sauna Build

Plywood isn't categorically banned from every part of a sauna project. There are structural applications where it performs well and poses minimal risk, provided it's separated from the heated interior by insulation, vapor barriers, and solid wood paneling.

Subflooring

Plywood makes a perfectly serviceable subfloor beneath the finished sauna floor material. In this application, the plywood sits beneath layers of insulation, waterproofing membrane, and a finished surface like cedar decking, ceramic tile, or sealed concrete. It never contacts the heated air directly. For outdoor saunas built on framed floor systems, 3/4-inch exterior-grade plywood over 2x6 or 2x8 joists (16 inches on center) is standard practice. Treat it with a water sealant on both faces and all edges before installation, and it will hold up for years.

Exterior Sheathing and Roof Decking

On the outside of the sauna structure, plywood performs the same role it does in any residential building — providing racking strength and a nailing surface for siding or roofing. When used as exterior wall sheathing behind house wrap and siding, or as roof decking beneath felt paper and shingles, plywood is entirely appropriate. It's outside the building envelope and has no contact with the heated interior.

Changing Room Walls and Ceiling

If your sauna includes a separate changing room or cool-down area that doesn't get heated to sauna temperatures, plywood can work as a wall substrate beneath paneling. The changing room typically stays well below 100°F, which keeps off-gassing at negligible levels. Many DIY builders use plywood as a shear panel in the changing room, then cover it with tongue-and-groove pine or cedar for a finished look.

Doors (with Limitations)

Some builders use plywood for sauna doors, particularly in budget builds. This is a borderline application. The door does contact heated air on one side, but it's a relatively small surface area compared to walls and ceiling, and modern sauna doors often incorporate tempered glass panels that reduce the amount of wood exposed to heat. If you go this route, use exterior-grade plywood and seal all surfaces thoroughly. A better option, though, is a solid cedar or hemlock door — or a tempered glass sauna door designed for the purpose.

Where You Should Never Use Plywood

The interior surfaces of the hot room — walls, ceiling, benches, backrests, and any trim or molding — should be solid, untreated sauna-grade wood. No plywood, no particle board, no MDF, no OSB. These are the surfaces that directly contact temperatures of 150°F or higher for extended periods, and they're the surfaces closest to your body while you're sweating, breathing deeply, and absorbing whatever the surrounding materials emit through open pores.

Some budget sauna manufacturers cut costs by using plywood as hidden framing or backing material inside the cabin walls, behind visible wood panels. This is worth asking about if you're comparing pre-built saunas, because the plywood may not be obvious from looking at the finished interior. The heat still reaches it through the paneling, and the off-gassing still enters the cabin air.

For bench surfaces specifically, the concern goes beyond off-gassing. Plywood's layered construction makes it prone to splintering at the edges when exposed to repeated moisture and heat cycles. Splinters on a surface that contacts bare skin in a hot environment are a safety issue, not just a comfort issue.

The Best Wood Alternatives for Sauna Interiors

If plywood is off the table for your sauna's hot room, what should you use instead? The answer is solid, sauna-grade wood — species chosen specifically for their thermal properties, dimensional stability, moisture resistance, and low VOC emissions. Here's a breakdown of the best sauna wood types for interior paneling, benches, and trim.

Western Red Cedar

Cedar is the most popular sauna wood in North America, and for good reason. It's naturally rot-resistant thanks to oils in the heartwood that inhibit fungal growth and insect damage. It has low thermal conductivity, so it stays comfortable to touch even at high temperatures. It's dimensionally stable under humidity swings, and it produces a distinctive, pleasant aroma that most people associate with the classic sauna experience. Cedar also has natural antimicrobial properties, which helps keep the interior hygienic between cleanings. Browse our full selection of cedar saunas if this wood appeals to you.

Canadian Hemlock

Hemlock is a lighter-colored softwood with a subtle grain and virtually no scent — making it an excellent choice for people who prefer a neutral sauna environment or who are sensitive to the strong aroma of cedar. It offers good heat retention, even heat distribution, and moderate moisture resistance. Hemlock is also typically less expensive than cedar, which makes it popular for budget-friendly DIY sauna builds. Many pre-built infrared saunas from brands like Golden Designs use hemlock as their primary construction material.

Thermally Modified Wood (Thermowood)

Thermal modification is a process where wood is heated to temperatures between 375°F and 480°F in an oxygen-free environment using only heat and steam — no chemicals. This permanently alters the wood's cellular structure, dramatically improving rot resistance, dimensional stability, and moisture resistance. Thermowood is the gold standard in Finnish sauna construction and is rapidly gaining popularity in North America. Common species include thermo-aspen, thermo-spruce, and thermo-radiata pine. Thermo-aspen in particular has become a favorite for sauna interiors — it has a beautiful dark tone, stays cool to the touch, and has extremely low VOC emissions. It's Haven of Heat's best-selling sauna wood for custom builds by a wide margin.

Aspen

Natural (non-thermally-modified) aspen is a popular choice in European saunas, particularly in Finland and Scandinavia. It's a hardwood with very low thermal conductivity, meaning it stays comfortable against bare skin at high temperatures. Aspen is hypoallergenic, resin-free, and has a clean, light appearance that works well in modern sauna designs. It's softer than cedar, so it does require more careful maintenance, but it's an excellent option for interior paneling and benches.

Alder

Alder is another European favorite, prized for its warm reddish-brown tone that deepens beautifully with heat exposure over time. Like aspen, alder is hypoallergenic and resin-free. It offers good dimensional stability and performs well in both traditional saunas and infrared models. When thermally modified, alder's durability improves significantly, making it suitable for both indoor and outdoor applications.

Basswood

Basswood is the most hypoallergenic North American wood commonly used in saunas. It has virtually no scent, no resin, and very low thermal conductivity. If you or anyone in your household has chemical sensitivities, respiratory issues, or allergies to stronger wood aromatics, basswood is worth serious consideration for your infrared sauna interior. The tradeoff is that basswood is softer and less durable than cedar, so it requires more attentive care.

Nordic Spruce

Spruce is the traditional sauna wood across much of Scandinavia and is still the most common species in Finnish saunas. Standard spruce can contain resin pockets that bleed when heated, but thermally modified spruce (thermo-spruce) eliminates this problem entirely while enhancing dimensional stability and rot resistance. Thermo-spruce has a rich, warm appearance and is widely used in outdoor barrel saunas and cabin-style builds.

Plywood vs. Solid Wood: Cost Comparison

The appeal of plywood is almost always about cost. A 4x8 sheet of 3/4-inch plywood runs $30 to $60, while sauna-grade tongue-and-groove cedar paneling typically costs $20 to $60 per square foot. For a 5x7-foot sauna hot room with an 84-inch ceiling, you're looking at roughly 200 square feet of wall and ceiling surface. In plywood, that's about $100 to $150 in material. In cedar paneling, it's $3,600 to $7,000.

That's a real difference, and it's why some DIY builders are tempted to reach for plywood. But the math changes when you factor in longevity, maintenance, and health. Plywood in a hot, humid environment will delaminate, warp, and degrade within a few years — often within months if it's directly exposed to sauna temperatures. You'll be replacing it long before solid cedar needs any attention beyond occasional sanding and oiling. And if health benefits are part of your reason for building a sauna in the first place, off-gassing formaldehyde into your breathing space works directly against that goal.

If budget is the primary constraint, consider hemlock or alder paneling instead of cedar — they run $10 to $40 per square foot and offer perfectly good performance in a sauna environment without the chemical concerns of plywood. You can also look into DIY sauna room kits that bundle pre-cut, kiln-dried cedar paneling with benches and hardware at a better per-square-foot cost than buying materials individually.

What About "Formaldehyde-Free" or Exterior-Grade Plywood?

You may encounter plywood products marketed as "no added formaldehyde" (NAF) or "ultra-low emitting formaldehyde" (ULEF). These are legitimate improvements — they use soy-based or polyvinyl acetate adhesives that produce significantly less formaldehyde off-gassing than standard urea-formaldehyde resins. The EPA's TSCA Title VI regulations, which took effect in 2018, also reduced allowable formaldehyde emissions in all composite wood products sold in the United States.

Exterior-grade plywood uses phenol-formaldehyde resin, which is more moisture-resistant and off-gasses more slowly than the urea-formaldehyde resin used in interior-grade products. It's a better choice for any structural application in a sauna build.

However, even "formaldehyde-free" plywood is not ideal for direct use in a sauna hot room. The adhesives may still emit other VOCs at elevated temperatures, and the layered construction of plywood makes it inherently less stable than solid wood under the extreme temperature and humidity cycles that a sauna interior endures. For structural applications outside the hot room — subflooring, exterior sheathing — formaldehyde-free or exterior-grade plywood is a fine choice. For the heated interior, solid wood remains the only appropriate option.

Building a Sauna the Right Way: Material Guide by Location

Here's a quick reference for which materials belong where in a well-built sauna:

Hot room walls and ceiling: Solid tongue-and-groove sauna wood — cedar, hemlock, thermo-aspen, thermo-spruce, aspen, alder, or basswood. No plywood, OSB, MDF, or particle board.

Benches and backrests: Solid sauna-grade wood, ideally thermo-aspen, cedar, or basswood for their low thermal conductivity and comfort against bare skin. Never plywood.

Hot room floor: Ceramic or porcelain tile, sealed concrete, or solid cedar decking over a waterproofed subfloor. Plywood is acceptable as a subfloor layer beneath waterproofing only. Learn more in our guide to the best floor material for saunas.

Structural framing: Standard 2x4 or 2x6 kiln-dried lumber (SPF or similar). Plywood is not needed here.

Subflooring: 3/4-inch exterior-grade plywood, sealed on all surfaces, beneath insulation and a finished floor. Acceptable use.

Exterior walls and roof: Plywood sheathing with house wrap and appropriate siding or roofing. Standard construction practice. Acceptable use.

Insulation: Mineral wool (Rockwool) or fiberglass batts with an aluminum foil vapor barrier on the hot room side. Avoid foam board insulation in direct contact with the hot room wall cavity.

Vapor barrier: Aluminum foil or foil-faced kraft paper, taped at all seams, on the hot room side of the insulation. This reflects radiant heat back into the room and prevents moisture from entering the wall cavity.

Should You Skip DIY and Buy a Pre-Built Sauna Instead?

If the material selection process feels overwhelming, or if you want certainty that every component in your sauna is safe and purpose-built for the environment, a pre-built sauna eliminates the guesswork entirely. Quality manufacturers use solid, kiln-dried sauna-grade wood throughout — no plywood, no particle board, no chemical adhesives — and engineer every component for performance in high-heat, high-humidity conditions.

Pre-built options include barrel saunas that ship flat-packed for straightforward outdoor assembly, cabin-style saunas with turnkey installation, and indoor infrared and traditional saunas that snap together in under an hour with no tools beyond a screwdriver. Many of these are constructed from thermo-treated or kiln-dried cedar and hemlock with no engineered wood products anywhere in the build.

A middle-ground option is a DIY sauna kit. These kits provide pre-cut, tongue-and-groove cedar paneling, bench materials, and hardware designed for installation in a room you've already framed and insulated. You handle the structure; the kit handles the interior surfaces with materials specifically selected for sauna use. This approach gives you the satisfaction and cost savings of a DIY build without the risk of choosing the wrong interior materials.

Finishing and Protecting Your Sauna Wood

Once you've invested in proper sauna-grade wood, protecting that investment matters. Unlike plywood, which you'd instinctively want to seal or varnish, solid sauna wood should be treated sparingly and only with products designed for high-temperature environments. Standard polyurethane, lacquer, and varnish will off-gas, blister, or become tacky when heated — exactly the kind of problem you're trying to avoid.

The best options for sauna wood finishing are paraffin-based sauna oils and natural sauna waxes that penetrate the wood grain rather than forming a surface film. These products reduce moisture absorption, minimize staining from sweat and body oils, and extend the life of the wood without introducing harmful chemicals. Our guide to finishing sauna wood walks through the process step by step, including product recommendations and application techniques.

The Bottom Line

Can you build a sauna with plywood? Technically, plywood can play a supporting role in a sauna — as subflooring, exterior sheathing, or roof decking. But it should never be used for the interior surfaces of the hot room. The formaldehyde and VOC off-gassing from plywood adhesives at sauna temperatures is a real health concern, the material degrades quickly under heat and humidity cycling, and it simply doesn't perform the way solid wood does in this demanding environment.

The good news is that proper sauna wood doesn't have to break the bank. Thermally modified wood, hemlock, and alder all offer excellent performance at accessible price points. And if you'd rather skip the material selection process entirely, pre-built saunas and DIY kits from reputable manufacturers give you a safe, purpose-built hot room without any compromise on air quality or durability.

Your sauna should be a place where you breathe clean, heated air and leave feeling better than when you went in. Choosing the right materials — and keeping plywood out of the hot room — is one of the simplest ways to make sure that's exactly what you get.