How to Build a Sauna

The tension-easing relief a sauna offers can do wonders. It’s a tradition historically linked to Finland, where pits dug in the sides of slopes were heated with fireplaces, hot stones, and steam. Luckily, it’s possible to build one of these cozy relaxation rooms at home without digging a hole in the side of a hill.

Read on to learn the basics of building a home sauna plus factors to consider before you begin.

How To Build a Sauna: The Need-to-Knows

Before building this luxury typically reserved for spas and health clubs, there are a few things to think about.

Inside or Out?

The most important decision to make when planning to build a home sauna is whether it should be located indoors or outdoors. An indoor sauna can be built in a closet, basement, or bathroom if the proper precautions are taken. Since the structure, electricity, and ease of access are already in place, building an indoor sauna can be an attractive option.

An outdoor sauna requires a separate structure, either newly built or repurposed. An old shed might make a great spot for a sauna, but it will likely need to be wired for electricity (depending on the sauna type). Otherwise, a sauna can be built on a deck, on grade, on a concrete slab, or almost anywhere else that’s level and flat.

Kits vs. Custom Builds

There are sauna kits available that come with almost everything necessary to turn a shed or interior room into a sauna, and they’re worth considering. But an experienced DIYer can save some money by building a custom sauna without a kit. The chief consideration will be the builder’s experience level. If you’re a seasoned DIYer eager to personalize your home sauna (and save a few bucks), a custom sauna is worth the work. If you’re less experienced and/or have time constraints, for speed and simplicity, go with a kit.

Heater Type

There are three heater types to choose from electric, gas, and wood. Electric and gas are both efficient and heat quickly, and they will typically require an electrician or plumber’s expertise. Wood may be a better option for building an off-grid sauna, though wood-fueled saunas take longer to heat, and the temperature is harder to control.

Materials Matter

Saunas produce high temperatures and moisture levels, so the materials used matter:

Wall insulation should be fiberglass batt
A foil-faced vapor barrier should be used over the insulation, and any seams should overlap by at least 4 inches
Softwoods like cedar, poplar, and hemlock will swell and contract without cracking. Cedar is the most desirable, as it’s antimicrobial and smells and looks great, but it’s expensive. In a pinch, rough pine will also work, though it won’t last as long.
Glass elements such as doors and light fixtures must be tempered to prevent cracking. And any electrical boxes or devices should be rated for high-humidity areas.

How To Build a Sauna: The Basic Steps

Building plans for home saunas will vary widely, but they’ll share basic characteristics that are important to note whether you’re DIYing it or enlisting a contractor’s help. The following steps explain the basics of how to build a custom electric- or gas-powered sauna of any size, with tips for indoor or outdoor builds.

1. Prepare the Location

Decide whether the sauna will be indoors or out and prepare the location. For indoor saunas, remove everything from the room, exposing the walls down to the studs. For outdoor saunas, find a flat, level spot large enough for the sauna.

Regardless of the sauna’s location, the floor should be waterproof. For outdoor saunas, this usually means starting with a concrete foundation. For indoor saunas, concrete board, waterproof floor membrane, and a skim coat of concrete or tile will typically do the job.

2. Install the Electrical

With the studs exposed, run wires for the electric heater if you’re using one, the thermostat, lights, and any other devices the sauna will include. Drill through the studs, run conduit, and pull the appropriate wires for the devices. If you’re using an electric heater, be sure there’s enough room on the breaker to handle its power draw.

3. Insulate the Walls and Ceiling

Install insulation between the stud bays and ceiling joists. Be sure to use the appropriately sized batt insulation for the stud and joist sizes (2×4, 2×6, 2×8, and 2×10 commonly) as well as the bay width (12, 16, or 24 inches, on center).

4. Install the Vapor Barrier

Install the foil-faced vapor barrier over the insulation, securing it to the studs and joists with staples. Install a lower course around the room before installing the upper course and then moving to the ceiling. Be sure that the upper course overhangs the lower course by at least four inches and create as few seams as possible. Where seams are unavoidable, seal them with foil tape.

5. Install the Paneling

Starting on the ceiling, install the paneling across the sauna space. For the first board, nail through the face of the board and into the joists, ensuring that the tongue is facing away from the wall. For each subsequent course, line the groove up with the previous board and nail through the tongue and into the joists. Repeat the process for each wall.

Note: Be sure to maintain a roughly ¼ -to ⅜-inch gap around the perimeter of the ceiling and each wall. This space will allow for the expansion and contraction that naturally occurs in a sauna. You can cover the gaps with small strips of paneling cut on a table saw.

6. Build the Bench

Measure the distance between two parallel walls. Build a simple frame with 2×4 stock and screws that spans the distance and measures 19 inches deep. Cut four 2x4s to 16 inches for legs. Situate the bench with a leg positioned vertically and flat against the wall in each corner. Screw the legs to the walls and then screw the frame to the wall. Finish the bench with 2×4 stock spaced ¼-inch apart.

7. Install the Heater and Light Fixtures

Install the heater in the sauna by either plugging in the electrical cord or plumbing the gas pipe (be sure to check gas piping for leaks). Install the light fixture(s), switches, and thermostat as well.

8. Test the Sauna

Set the thermostat to the desired temperature and close the door. Wait the suggested amount of time before checking the temperature in the space. Use the dipper spoon to pour a bit of water over the heater’s rocks, and enjoy the sauna’s relaxing, steamy atmosphere.

Tools and Materials

The tools required for building a home sauna will vary depending on the size and design. A general set of hand and power tools will be necessary, including:

Materials will also vary based on design, but in general:

2×4 or 2×6 framing lumber
Cedar, poplar, hemlock, or pine tongue and groove paneling
Concrete
Nails, screws, and staples
Waterproof membrane
Floor tile and thinset
Sauna heater and thermostat
Electrical boxes, fixtures, and wiring
Fiberglass batt insulation
Foil-faced vapor barrier
Foil tape

Bottomline

With your newly built home sauna, you’ll be able to enjoy a steam bath any time, even without a fancy spa membership. You can get as creative as you’d like with this basic design, so feel free to build the sauna of your dreams.