How to Build Wood Sauna Benches

After a couple weeks of hard work installing the interior wall planks in my sauna, I was eager to move on to what I thought would be the easy part—building the sauna benches.

Turns out, it wasn’t as straightforward as I had imagined.

Between selecting the right materials, deciding on the dimensions, and planning out structural support, the process ended up taking quite a bit of thought and research.

If you're in the same position, scratching your head over bench height, board spacing or what type of wood to use, I’ve put together these notes based on my experience. Hopefully, they’ll help guide your build and eliminate some of the trial and error.

Bench Dimensions: Depth, Height, and Placement

Top Bench Depth: A comfortable top bench depth is around 22–24”. If you plan on adding a backrest or leaving a gap between the bench and wall for airflow, factor that into your measurements.

Lower Bench Depth: This can vary depending on available space. It's typically narrower than the top bench but can be wider if you plan to use it for lower seating. One thing that isn't negotiable in a traditional sauna - it must be placed a safe distance from the stove.

Bench Heights: This is probably the most discussed issue in the sauna building community and one of the first criticisms that pops up when someone posts a photo of their sauna. “Benches are too low” is almost a guaranteed comment over at r/sauna.

While there are some guidelines from Finnish sauna design, often times the space available in the sauna is going to heavily influence the bench height or size. Based on Finnish design the space between the top of your head (while sitting) and the ceiling should be about two fists—roughly 40-44” from the ceiling to the top bench.

The vertical spacing between the lower and upper bench is commonly 18”, but you can adjust this to fit your height and comfort. Try sitting in an adjustable office chair to get a feel for what bench height works best for you—feet flat on the floor is what I was aimed.

Then there is the golden rule, keep the lower bench roughly the same height or above the top of the stove’s stones. This is where the ‘bench too low’ comments come from. This can be challenging in some setups, such as a barrel sauna, where it's just not possible to get the benches that high. If that’s not possible, consider adding a footrail to elevate your seated position for better heat exposure and comfort.

If this detail is making you sweat, just remember, any sauna is better than no sauna.

Choosing the Right Wood for Sauna Benches

Cedar is a classic choice in the US—and for good reason. It’s naturally sap-free, resists rot, feels soft and its knots are usually small and tight, meaning fewer hot spots that can cause burns.

Other common wood varieties include Alder, Aspen, and Hemlock, just to name a few. Whatever you choose, make sure it’s low in sap content and, ideally, clear of knots. Avoid resinous woods like pine or spruce for areas where skin contact happens—sitting on hot sap is not going to be enjoyable. However, these construction-grade woods can be used for hidden supports or internal framing.

Bench Framing & Support

For most sauna bench builds, 2x4’s are a solid choice for the frame. To prevent sagging—especially on longer spans—you may want to add support in the middle of the bench. This could be a diagonal brace to the wall or a vertical support down to the floor. If you're spanning a larger distance, consider using 2x6’s for the frame.

To calculate how much flex your bench will have, I recommend using an online sag calculator. Since the bench will be supported on the back wall which will carry some weight, these calculations are not perfect, but a good reference.

You can also try using ChatGPT to calculate the sag based on your specific needs. Try the prompt below, just replace the dimensions, wood, weights ect. to match your design.

AI Prompt:
I am building a 24" deep x 6' long sauna bench with rectangular box frame made from #1 grade 2x4 cedar. There will be horizontal supports between the back and front rails, spaced roughly 16” on center. The bench will be secured on three sides with one side spanning the length unsupported. If three people with an average weight of 175lbs were sit on the bench evenly spaced, what would be the estimated sag?

Bench Tops: Material, Spacing and Fastening

For bench planking, I used 5/4” cedar deck boards. They’re sturdy, comfortable, and came with redounded edges that saved me time. If you want an even beefier feel, you can go with 2x4s, which can be seen in this blog post from Sauna Times.

Plank spacing is somewhat personal and often dictated by the overall dimensions of the bench and the lumber used. I landed on a 5/8” gap between boards since the deck boards were 5.5”, frame boards were 1.5” each and my total bench width was 22”. With three planks, roughly is what worked.

Reading through some comments on various forums, the general consensus was that less than ½” can make cleaning difficult and limit airflow and more than 1” could start to feel uncomfortable. Whichever you use, fastener placement is critical—burns from exposed metal are no joke. Hidden fasteners are a must. I screwed mine from underneath to keep the top surface clean and safe.

Finishing Details

• For visible screws in the bench frame, countersink and plug them for a cleaner, professional look.
• Mounting the frame to the wall? Make sure to plan screw placement around your wall blocking or studs so you don’t run into conflicts later on.
• Use stainless steel screws whenever possible to avoid corrosion. If those aren’t an option, triple-coated deck screws that are approved for use with cedar (or type of wood you are using) will work.
• A nice finishing touch on the benches is to use a router to round over the front edge of the bench. This little detail not only enhances the appearance but takes away the sharp edge that digs into the back of your knee.
• Once everything is complete, a good sanding is all that is needed to make sure there are no splitters or rough edges. Always sand with the grain to avoid leaving cross scratches.

Mounting the Benches to the Walls

For anchoring to the wall, structural rated screws are the right choice. They are heavier and have a higher sheer strength than regular construction screws, so they are necessary for safely supporting the benches, especially floating benches. The cost is worth peace of mind, in my opinion.

Whichever fastener you choose, it is important to screw into a structural member in the wall, whether that is a stud, blocking or solid timber. Screwing the bench into just tongue and groove wall boards will not provide sufficient.

Protecting Your Hard Work

Once the benches are built, it’s worth taking the time to apply Sauna Wood Oil and/or Bench Wax. These products protect the wood from moisture and stains, prevent dirt from settling into the grain, and make future cleaning much easier.

Final Thoughts

Building sauna benches is a fairly straightforward project, but the details make it very personal to your sauna —functionality, comfort, and safety all come into play. With a bit of thoughtful planning and a focus on quality materials, you’ll end up with a bench that not only looks great but performs beautifully for years to come. Let me know if you have any specific questions about the build process. Sauna craftsmanship is a journey—and I’m happy to help others enjoy the ride.

DIY Sauna Bench Building Guide

Standard Dimensions: 6’ long × 22” wide × 3.5” tall (fully customizable)

Materials and Tools

Lumber

• Cedar decking boards (typically 1" × 5.5") – for the top surface
• Cedar 2x4s (1.5”x3.5”) – for frame and support structure

Hardware

• Stainless steel wood screws
• Moisture Rated Wood glue (optional)
• Wood plugs or dowels (optional for concealed joinery)
• Structural Screws (for anchoring benches to wall)

Tools

• Miter saw or circular saw
• Drill/driver
• Countersink drill bit (matching wood plug size)
• Clamps
• Measuring tape
• Carpenter’s square
• Sandpaper or sanding sponge
• Router (for edge detail, optional)
• Sauna-safe finish (Sauna Seal)

The Build

1. Plan Your Dimensions

   Example size:

   • Length: 6 feet
   • Width: 22 inches
   • Height: 3.5 inches

   Adjust the length, width, or height to fit your specific sauna space.

2. Cut the Frame Pieces

   Cut the following from cedar 2x4s:

   • (2) Long sides: 72" (or custom length)
   • (2) Short ends: 19" (for 22" total width, accounting for 1.5" side thickness)
   • (5) Cross braces: 19" each (space evenly for support) These will need to be ripped down to accommodate the inlayed bench decking (5/4”).
     
     

3. Assemble the Frame

   • Predrill holes and countersink in the face of the long front and back rail using a counter sink bit.
   • Countersink deep enough to accommodate a wood plug to conceal the screw head.
   • Assemble the rectangular frame with wood glue and stainless screws.
   • Make sure to check the frame for square as you go.
   • Attach cross braces for support, spacing them roughly 16" on center.
     
     

4. Inlay the Decking Top

   a. Measure and Cut the Decking Boards

   • Cut decking boards to approximately 69" (to fit inside 72" frame).
   • You will typically need 3 boards for this size, but adjust for your design/material
     
     

   b. Install Without Exposed Fasteners

   • Position boards evenly with even spacing and gaps.
   • Check the frame for square and adjust as needed.
   • Attach the decking from the underside using screws through cleats or the cross braces.
   • Avoid visible screws on the bench top.
   • Use clamps to hold boards in place while fastening for precision.
     
     

5. Sand and Finish

   • Sand all surfaces (start with 120-grit, finish with 220-grit).
   • Round over the front edge with a router for comfort and clean design.
   • Apply sauna wood or wax to protect the sauna bench from moisture and dirt.