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DIY Home Sauna—It's Like a Sauna in Here!

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Jim is a retired software/electrical engineer who enjoys the outdoors. He likes to challenge himself with creative projects at home.

Outdoor saunas are rooted in tradition.

Outdoor saunas are rooted in tradition.

How to Build a Home Sauna

Since I became a homeowner several years ago, I always wanted to build a sauna.

Here in Michigan's Upper Peninsula, the sauna was popularized by Americans of Finnish or Scandinavian heritage.

A sauna is a small hot room (140 °F to 200 °F) where you go to sweat. It promotes relaxation and encourages good health.

I’ve seen a few inside of homes and a few outside of homes, as well as some in spas and health clubs.

A popular activity, though somewhat peculiar, is to heat yourself in a sauna and then go roll in snow or plunge yourself into cool water. This can be very—shall I say—invigorating.

Step 1: Selecting a Location

I thought of purchasing a kit with an electric heater and putting the sauna in the basement. I also thought of building a room on my deck near the house.

But I also happened to have an old, concrete block outbuilding that was used to store nothing but junk. It was not too far from the house. Voila, the perfect location for a sauna!

I also had an old iron fireplace insert sitting around just slowly rusting. Voila, a perfect sauna heater!

Finally, it was decided. Thoughts of my own sauna lurked around in the dark recesses of my twisted mind for years, and finally, an outdoor wood-fired sauna is what I would build.

Step 2: Cleaning the Outbuilding

The first step was to clean the outbuilding and throw away any unusable junk that had accumulated for the past several years.

There were vines growing into the building from an uncovered eve and mud-dauber wasp nests throughout.

One half of the ceiling was covered with paneling, which when removed, sent a shower of dirt and assorted debris down onto me.

After removing hundreds of nails, I was ready to measure and mark the space.

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Step 3: Drafting the Design

Over the years, I refined the plans and made several hand drawings and CAD drawings as I mulled over the perfect sauna project.

When I decided to use the outbuilding I had sketched, my plans began to solidify my design. As usual, once I discussed the plans with my wife, they changed. She is not a CAD wizard, so she sketched her version in chalk on the driveway.

Shortly after, I began working on the sauna interior according to my wife's chalk sketch. We decided to divide the interior space into three rooms: the sauna, a changing room, and an entry/storage area.

Step 4: Constructing a Hearth

Next, I constructed a hearth to house the iron fireplace insert.

After much contemplation, I located its position in the sauna room space and decided to run the chimney straight up through the roof.

To construct the hearth, I used concrete blocks (which I’ve always called cinder blocks, perhaps incorrectly) as the base. The hearth walls and top were constructed of concrete bricks. It took more blocks, bricks, and mortar than I imagined. I used angle iron pieces I had cut from an old bed frame along with pieces of scrap sheet metal to span the walls and hold the bricks in place for the top. All was held together with masonry cement.

In a standard design, a sauna stove usually heats rocks onto which water can be dripped to add steam. Since the top was enclosed with brick and the stove was a steel enclosure itself, I didn't anticipate much heat transfer to the rocks. I added some anyway for decoration. If I wanted some steam, I could place a pan of small rocks on the top steel ledge of the stove where the blower outlet holes were located.

Before installing the heavy 300+ pound insert, it was repainted with flat black high-temperature wood stove paint from Home Depot. Then, it was positioned in front of the hearth before the top bricks were placed and hoisted using a come-along and a nylon tow strap draped over a post in the rafters. It slid right into place with only 1/4" clearance on either side. (A bit of advice here: Measure carefully several times before building the hearth.)

The stove protruded somewhat, and the bottom was designed to be set on a ledge of the fireplace. This threw the balance out slightly and made the stove want to tip outward, so I placed a block under the bottom front for it to rest on.

Drafted order summary from woodlanddirect.com.

Drafted order summary from woodlanddirect.com.

Step 5: Constructing the Chimney

Once I decided to run the chimney straight up through the roof and not through the sidewall, I needed to find chimney components. I was looking for a metal, double-wall chimney system to be fire safe and to minimize the clearances I needed. I figured I could use a single wall stovepipe up to the ceiling of the sauna, then a double wall the rest of the way.

I began an online search and settled on a company called woodlanddirect.com. They seemed to have a very large selection of components. I used their chimney design wizard to specify the components I needed, but when the price tag approached $800, I thought I could order “a la carte” and save some money.

When the parts arrived and I tried to test fit them together, I found that nothing worked. I called the company and timidly explained that I didn’t know what I was doing and needed help.

The technical salesperson explained that nothing I had ordered would fit together. They were very cooperative with the return and helped me order the correct chimney components. I ended up at about $100 more than my first order, but still way less than $800.

Step 6: Cutting the Clearance Hole

I hung a plumb bob from the ceiling over the outlet of the stove and marked the inside of the roof to cut the clearance hole. I “dry fitted” everything together from the stove to the chimney cap, then secured it with extra bracing between the rafters. This building had a sheet metal roof and I thought I could flatten the ridges of the sheet metal with a big hammer and then place the chimney flashing over the top. That did not work.

Instead, I cut the flashing to fit between the ridges along its sides and then formed it over the roofing ridges along the top and bottom. I applied a very generous amount of silicone roofing cement.

Just to be sure the stove and chimney were really doing the job and to check for smoke leaks, I started a test fire with a large wad of newspaper. Smoke came from the top of the chimney and nowhere else. It is recommended that the chimney terminates at least 2' above any obstacles, including the roof peak. I know that if the chimney is not high enough, it will not draw well. My chimney is about 3' above the roof peak. In hindsight, I probably should have run a stress test with a full-blown fire in the stove.

Step 7: Framing

I started framing before I installed the chimney and completed the task once the chimney was installed. Since I knew that the paneling would not be pieced together and would span the entire length of each wall, I was not too strict with stud spacing—they were placed on 24" centers. Between each stud, I placed 2" thick Styrofoam panels (approx R-10 value) and sealed the gaps with Great Stuff expanding foam.

I found that using a reciprocating saw with a fine-tooth blade works well for cutting the panels. I wondered a little about whether the "R" value would suffice. The building is made of 9" thick cement block walls, so I left about a 1" air gap between the insulation and the block; the paneling is 3/4" thick cedar. All of this adds some extra insulation.

The stove is oversized, almost Binford-sized, so I didn't anticipate a lack of heat. I did find, due to my lack of carpentry experience, that I needed to add a few strips of particle board inside the 2 x 4 boards at the corners where the walls met. One wall had a place to nail the end of the paneling and the other perpendicular wall did not. It all worked out.

Step 8: Rewiring and Moving the Breaker Box

I had to move the breaker box from what is now the entry into the new storage area. There were two large, wooden posts (approx. 8"x 8") that partially supported the span of the roof trusses. They didn’t really help that much to support the structure since they were just wedged in place and held with a few nails through a truss. I moved one of them to the storage area; the breaker box was mounted on it.

I added a recessed LED ceiling light in the sauna room, a cheap ceiling fixture in the changing room, and an even cheaper ceiling fixture in the entry. Of course, I had to add switches for each light.

I also wired one electrical outlet in the sauna room (for the blower on the stove) and one in the changing room. At the time of this writing, the changing room light fixture was not installed since the ceiling paneling was not attached yet.