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How to Build a Sauna: Completing the Job

Licensed contractor Paul Ryan shows how to build a sauna from a pre-cut kit. Tongue-and-groove walls, benches and windows complete the custom sauna project.

More in Bathroom

unfinished basement room could use makeover
  • Time

    Several Weekends

  • Price Range

    $2,500 - $5,000

  • Difficulty



Step 1: Install the Windows and Finish Exterior Walls

In the previous phase of the project, we placed the tongue-and-groove walls on the inside of the entire sauna. Use a reciprocating saw to cut out the windows (Image 1).

To finish the exterior walls, apply fiberglass insulation between the wall cavities to help retain sauna heat (Image 2).

Install the exterior tongue-and-groove walls just like on the inside, including placing boards over the windows as it's easier to cut out them out later than to cut the tongue-and-groove boards to size.

Once all the exterior boards are nailed in, install the tongue-and-groove soffit overhead along with the fascia board (Image 3).

Cut in a switch for the sauna lighting.

Step 2: Install the Sauna Heater

A lot of sauna heaters will have only a small pan of rocks which produce only a quick burst of steam when you add water. In our project we used an 18" deep chamber to produce more consistent steam and heat (Image 1).

Follow the manufacturer's instructions for mounting the heater. In our project, the 220-volt heater sits on the wall, supported by two screw brackets (Image 2).

Note: Be sure to have an electrician hook up the heater.

The heater rocks are dense rock from Scandinavia called vulcanite. Rinse the rocks before placing them inside the heater, placing the smaller rocks around the outside of the compartment and larger rocks in the center. Allow for space between the rocks to give the heater optimum performance, saving any extra rocks for replacements.

Attach the supplied heater-guard pieces to the heater, which can be moved out of the way but will prevent unexpected heater burns.

Note: The water all steams away, so no drain is needed for the sauna heater.

Step 3: Add the Benches, Trim and Finish the Windows

Measure from the floor and mark a line on the walls where the top edges of the bench supports (Image 1) will be fastened. Each support is long enough to span at least two wall studs.

In our project, we used benches with long supports to allow slide out for easy cleaning. Using a minimum of two 3" screws, install the supports to the wall. Check to make sure they are level.

For the L-shaped top bench, drill through the frame holes with a 3/8" bit and then bolt the two benches together.

Every sauna needs fresh air when in use, so it's important to install a slide vent (Image 2) on the wall. Note: Keep the vent closed when heating up the sauna.

Set the lower bench in across the support brackets and then the upper bench.

Put in the H-bracket (Image 3) to support one end of the side bench. Set the bench down over the end and go underneath to attach the bench section with lag screws.

Next, install the cove and corner moldings. Trim the cover molding as needed to ensure a tight fit.

The 3/4" x 3/4" corner molding is used to trim the corners of the room where the walls meet. These will cover the face nailing that starts and ends each wall.

Set the two windows in place in the openings. Shim them into place and make sure the glass aligns with the glass on the door.

Secure the windows with screws through the jamb (Image 4) and into the wall frame.

Step 4: Install the Lighting and Finish the Job

For this particular sauna kit, strip lighting was installed along the back wall. Follow the kit instructions. In our project, the kit came with a pre-hung, glass door (Image 1). Install the door, following the instructions.

We also installed halogen lights over the door.

Paint the surrounding drywall before installing any flooring around the sauna. In our project, in a fitness center area, we installed interlocking floor tiles made from recycled car and truck tires (Image 2) for its anti-fatigue and sound absorbing qualities.

Note: While the sauna floor is wood in our project, tile is a popular sauna floor choice. In addition, heat-resistant interlocking vinyl floor tiles can be installed over wooden sauna floors for extra protection and comfort.

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