Finnish Sauna

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Introduction: Finnish Sauna

Growing up, I was always intrigued by saunas. I'm usually not one for extreme temps in either direction, but there's just something about a sauna that speaks to the soul. They're relaxing, cleansing, and a great way to soothe your body after a long day's work in the winter.

I probably never would have pursued this had it not been for my wife. In 2011, we met in Scotland, both attending the same grad school. She's 1/2 Lithuanian, and 1/2 Russian and grew up going to saunas with her family.

In Russia, it's a right of passage. Men and women visit gender specific saunas, and it's not uncommon to find a grandfather enjoying a "bath" with his son and grandson while passing down the family's secrets.

In Lithuania, families can rent private sauna villas for the day. You grab your key from reception, go to your private room that looks just as any other hotel door would, but enter into a luxurious suite with a small wading pool, hot tub, sauna, and dining room. My wife has told me stories about her childhood when her mom, dad and brother would go for the day, and rotate between the water and steam sauna, playing with dad in the water while mom relaxed with a smile. You'd think this would be pricey, considering how lavish it feels and how well the craftsmanship is throughout, but they're actually quite reasonable. Even today, the nicest of sauna suites can be rented for under 20 euros/hour. Often connected to luxury hotels, you can also enjoy room service without ever having to leave the comfort of the suite.

Let me just say that after my wife took me for my first Lithuanian sauna experience, I was hooked. When she asked me to build her a sauna after we purchased our new home, it didn't take a lot of arm twisting for me to agree...

I started the project in October of 2016, had it weather tight within a couple weeks, and then it was just weekends here and there until I had a week off during the winter, making significant progress. By early February, it was insulated and had power, and by late march it was usable.

Sauna's aren't a lot of fun in the summer, so it sat unused, but we had a comfortable and mild start to the summer so my weekends were spent finishing up the details, siding, stain, etc.

I still haven't applied the poly finish to the pine in the changing room, but I think it's ready for me to start putting together this blog. As fall sets in, we're using it more and more, and are loving it...

Step 1: The Joys of Planning...

Here's some pics of the initial building inspiration and the plans I sketched out.

I’m a bit OCD, so I tend to sweat the details. I probably spent over a hundred hours reading blogs, watching DIY videos, and shopping for specialty parts. I purchased most of the building supplies at the local big box store, the sauna equipment from a specialty supplier in NJ (West Sauna Bath), and a ton of detail stuff and tools from Amazon.

Along the way, here’s a brief summary of the key decisions that were made early on that shaped the project:

  • I would build a detached shed for the sauna. Our basement is unfinished (that's my winter project this year), and I considered putting it down there, but then I realized that I don't know what I don't know, and I don't know a lot! I was afraid I'd make a mistake, and would end up with moisture and mold infecting my house. Also, I like the detached "Finnish" sauna experience. It's my escape. Additionally, I designed and built it in a manner that if I ever start to question why in the world I built a sweat box in my backyard, I could convert it to a small studio office space.
  • The building would be roughly 8x12, divided into two 8x6 rooms: one for the sauna, and one as a changing room. These dimensions were very efficient and created very little waste. 6x8 is also a fairly large sauna. My wife and I are the only ones using it, but it could easily hold 6, so we have plenty of room to stretch out being just the two of us.
  • The sauna would be cedar lined, but I️ would not spend the money on clear cedar (except for the benches). Instead, I️ got the regular WP4 cedar tongue and groove boards to line the sauna room, but sourced them from a small town lumber yard nearby. The quality of their wood was far superior, and only about 15% more $$$ than the big box store. The size of my order allowed me to sort through it based on how clear (free of knots) each piece was. I️ ended up with several perfectly clear boards that I️ saved for the areas that would be a backrest and had plenty. In total, the cost of this cedar was about 1/3 of what it would have been shelling out for clear, and I have zero regrets.
  • The changing room would be pine car-siding. Cheap. Looks good. Got it from the big box store and just used premium grade 1x3 and 1x4 for all the trim and moldings. Has a modern cabin feel.
  • Electric over wood burning heater. At the end of the day, I wanted power to the building anyway, and while the thought of a wood burning stove was attractive in theory, I think I chose wisely when I considered all the additional work over the life of the sauna it would require for everything from getting the wood to cleaning all the ash that a wood stove would produce.
  • Definitely wanted steam capabilities, so I made sure to follow all the protocol for the damp environment: exhaust fan, the right heater & rocks, waterproof floor, aluminum faced insulation, with seams sealed using heat resistant aluminum tape.
  • Skid foundation - by far, the easiest foundation. Took 1/2 a day. No concrete. easy on the back, and structurally sound for a building this size. I did, however, opt for 6x6, even though all my research said 4x6 would have been plenty.

Step 2: Foundation

This was easy. I cut out 2 parallel trenches, each 12" wide, and spaced so that my 6x6x12' skids would be exactly 8' apart from outside edge, to outside edge. dug the trenches down about 6 inches, filled with gravel, and compacted it all down. I now had a sturdy and level base to start from.

Step 3: Joists & Subfloor

I went with 2x8s for the joists and around the perimeter. Spaced 2' apart on center. I also grabbed some cheap 2x2s and made a border in each joist cavity, 2" recessed to accommodate a 2" piece of foam insulation board with an R10 insulation value. Cut each one 22.5" wide and glued them down snug into each opening. Secured everything to the skids with 4 galvanized elbow brackets & galvanized lag screws on each side.

Step 4: Framing, Window, Door & Metal Roof

I pre-cut every piece of the framing the night before and marked them all based on which wall each was for, and marked them up for where everything fit together. I needed a buddy to help put the walls up, and this allowed me to maximize the time I had an extra set of hands when I needed them most.

I also shopped around and found a good deal on a door and window that had been returned to the big box store. Ultimately, I haggled them down to 75% off and got a steal. I needed these for the rough opening measurements.

I also decided to put in a transom window above the door. More on that later, but I love what I ended up with.

Sheathed with an aluminum faced OSB. The aluminum facing does not require house wrap/Tyvek, and also adds an additional R1 value of insulation as a thermal barrier. When you factor in the savings of no house wrap, I think I came out ahead with this choice. It also went up nicely.

For the roof, I chose metal, in bright red. It will last longer than shingles, installed much faster, and looks better. I didn't take many pictures on roofing day. Oops.

Step 5: Interior Framing & Insulation

Insulation is pretty important in a sauna, and you've got to be mindful of moisture. So I chose an aluminum faced mineral wool insulation for the sauna area, and aluminum faced fiberglass in the changing room.

As I framed up the dividing wall, I also needed to bring the ceiling of the sauna side down to about 7' and level. I just used 2x4's to frame it up, 16" on center so that I could add more insulation. This created a void between the sauna and the roof, so I went nuts with the insulation and just put any leftover scraps up there. I also insulated the ceiling bays with some pretty thick fiberglass rolls of R40.

Inside the sauna room, I sealed all the foil seams with a heat resistant, 3" foil tape. By the time I was done, it was practically air tight.

Step 6: Electrical Wiring & the Transom

I dug a trench about 2' deep in my yard to run a line from the house to the sauna. This is an area where I don't trust myself as much, so I hired a buddy who's a union electrician to run the big wires from the panel in my basement out to the building. He spent some time on the project, and only charged me a few hundred bucks for parts and materials.

He also helped me run all the high voltage lines for lights, outlets, and the power from sauna the control box (the brains) to the heater itself. It's good to have skilled friends!

Since I only had a few outlets and switches to install, I wasn't as worried about price, and wanted something that would really make a statement. Legrand makes a series of outlets and switches that are square, and have a cool and unique look to them, so I went with those.

At some point during the project, I went down the rabbit hole of research on low voltage LED lighting. It started because I wanted to run multi colored LED strips around the perimeter of the floor in the sauna itself. I ended up also creating a custom transom window, with a thermal pain on the outside, and a stained glass panel on the inside, with recessed LED light strips in between to make it glow. This turned out to be my favorite detail of the entire build.

The sauna controller has a connection for a fan, so I framed out an opening that would allow me to install an industrial grade fan inside the wall in the sauna to pull air from the sauna outside, and replace it with fresh air from the changing room by cracking the window. With the fan running, it's pulls all the moisture out in minutes, and with it off, but the vent open, it slowly recycles with fresh air to prevent it from becoming too musty. I framed the opening out in cedar, and bought a cedar vent cover from some place I found online. On both sides, I put up some stainless mesh to keep tiny critters out, and fingers from getting into the fan.

Around this time, I also realized that the 12kw heater I initially purchased was overkill, and I needed to down size to a 9kw. The folks at West Sauna Bath were really good to me, and made for an easy exchange.

I ended up with 3 outlets:

2 that are along the outer wall int he changing room. the third is actually burried inside an area I framed up between 2 studs on the back wall. This became my hiding place for all the LED controllers. There are 2 LED power supplies, one for the sauna lights, and another for the white LED inside the transom. I wired it up so that one plug of the outlet would be on/off at a switch on the wall for the transom, and also have a dimmer controller hiding in that cavity so I can control the brightness of the transom. The other plug of that outlet is "always hot" and powers the sauna LED lights which are controlled by a fancy looking LED touchpad controller I found on Amazon.

At about that same time, I was also running cat-6 cable throughout my house, and a friend has some direct burial cat-6 cable laying around. This allowed me to run an ethernet line from the sauna to the punch down panel I installed in the basement, and just buried it in the same trench as the power line. I might have the world's first Finnish Sauna with a hard wired Ethernet connection... Not sure what I'll ever do with it, but the thought was that I could add a wifi router from the sauna to cover the backyard if I ever need to, or if I ever convert it from a sauna building to a studio office, I'd already have the connection there.

Step 7: Interior Finishing

I sourced WP4 cedar boards from a local lumberyard for the sauna, saving the clearest pieces to go on the wall where it would be a backrest. The knots can get warm, so you want those where you won't lean onto them.

I used stainless steel brad nails for everything to prevent rust.

The changing room is all pine car siding from the big box store.

I installed an overhead light in the changing room, and an antique looking exterior light.

Between the sauna and changing room, I wanted to let some light in, so I went back to the local glass shop that made my transom window. I was shocked at how cheap they were ($23 for the transom), so I asked about a 40x40" thermal pane. It was only $60, and really opened up both spaces. Well worth it.

For the floor, I went with a vinyl click together waterproof flooring. it looks like wood, but is completely water proof. The floor of the sauna doesn't get very warm (heat rises!), so my only concern was moisture. It was cheap ($100 for a few boxes) and went in quickly and with ease.

Corner-round trim in the changing room to cover the gaps I left while learning how to install carsiding. Wasn't needed in the sauna, as I did that room last, and learned from my mistakes in the changing room.

Around the multi-colored LED in the sauna, I used the router to create some molding I could hide it behind. It's raised off the floor just enough that the light simply glows from the bottom of the walls.

Step 8: Benches & Interior Door

The benches are the only thing I used clear cedar for. It wasn't too pricey, and considering this is what I'll be sitting on, I wanted something that would be smooth and free of knots and splinters. I sanded the heck out of each 2x2" piece, and cut them down to slats.

I designed the benches to be removable, but attached cedar 2x4s horizontally to the studs with 4" stainless lag screws for support, while the benches themselves just ride on the rails and are held snug by neighboring pieces.

I'll see if I can get some better pics of this to show you how I built them, but each level is 2 removable pieces that make each "L", and they're sturdy as a rock.

I custom built my own door using a sheet of 3/4" plywood, and then lining each side with cedar & pine. I found some heavy duty stainless steel gate hinges, and called it a day.

Step 9: Siding

This is the part that I struggled with so much. Cedar siding is about double the price of other siding options. Even though this is a tiny little building, I still spent about $1,000 on cedar bevel siding. It hurt spending that much on such a small space, but I'm glad I did. Vinyl siding would have looked like crap compared to this. I also considered a cheaper material for the back (my neighbors see it, I don't), but I would always know it's there, and it would have bothered me.

Note - be sure to use Stainless steel nails for the siding. Anything else will leave stains as it streaks over time.

For the stain, I chose a translucent (NOT the same as semi-transparent) stain in cedar tone from Benjamin Moore Paints. It took two gallons and only required a single coat. I really like the translucent look, as it keeps all the grain detail.

Step 10: The Birds...

Around this time, my old pal James introduced me to his bird cam. It was a project he backed on kickstarter, and took amazing photos of birds. It's called the Bird Photo Booth 2.0. I started posting pics on social media, and got as many comments about the "sweet shed" in my backyard as I did about the critters, so I knew I was on to something.

I think I spent like $150 on the entire photo kit, total.

Worth it.

Step 11: The Finished Product...

I painted the door to match the roof, and added a coconut hair flower planter in the window. For this year, I built a small landing/step, but next spring I'm going to build a large deck on the front for a hot tub.

One of the outlets is at chest height in the changing room, and we added a little shelf for a place to put a radio, and a few sauna supplies.

We also put up birdhouses, using pulleys and a cleat on each side to make it easy to raise and lower them for cleaning and refilling. In the summer, we put up hummingbird feeders, and then some seed feeders in the winter to attract Cardinals.

If you have any questions, or need me to clarify anything, just leave a comment below and I'll do my best to answer them quickly!

Special thanks to:

  • My brother from another mother, Jerry, who loaned me his truck on several occasions for trips to the lumberyard.
  • James, who introduced me to the Bird Cam.
  • My buddy Matt who helped with the framing.
  • Dirk & Laura - My electrical gurus.
  • My wife - who was super supportive and let me use the sauna as an excuse to not do house chores.
  • My pops - who taught me the basics of building.

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44 Comments

Do you have any thoughts on any pre-fab sauna kits? Most seem to be electric/infrared (Health Mate), but some offer gas (Finnleo, Scandia etc).

I'd love to go gas gas/fire since electric saunas seem to take longer to heat up, and don't get nearly as hot.. plus I rather pay the higher installation cost rather than the higher operating cost.

A tiny closet-size gas indoor sauna in the garage would be ideal, with vent plumbing to the outside, but not sure if it's considered safe (or if it's even permitted in my area). Any idea if it's do-able?

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If going electric, might as well do the the portable neck-down saunas from Therasage.

I looked at some prefab kits when I was doing my initial research. Ultimately, I decided to build my own. This saved a bunch of money compared to the prefab units, and I was able to build it just how I wanted it. All other things being equal, I would have preferred a gas heater, but the costs got out of control when I started adding it up. It's certainly doable to build out a sauna into pretty much any area, including your garage, but you'll have to be mindful of the venting.

I have a 9kw heater, and it gets up to temp in about 20 minutes. It also gets pretty hot (190+ F, at the ceiling). This is plenty warm, and i've never felt like it wasn't hot enough. I set it to about 175, and find that to be about perfect for my preference.

That is a nice building! Glad I was able to help inspire a bit, love the upgrades!

i HAVE HAD A SAUNA FOR 30 YEARS AND IT IS HEATED WITH WOOD. i HAD BEEN IN ELECTRIC SAUNAS BEFORE THAT AND THEY WERE COLD AT THE FEET LEVEL IN THE DEAD OF WINTER. i WOULD RECOMEND A WOOD FIRED SAUNA

How this kind of heating works? Where the hearth for wood is located -outside sauna? how the stove is mounted?

I like this, but have no idea how to resolve wood heating...

My "heater" is an old propane tank that has been cut to 30" long and a door installed on the open end. A chimney hole cut into the top on the other end. The heater is placed through the sauna wall with the door that opens into a small room where I keep the wood and feed the fire. I filled in around the heater with pieces of block and mortar sealing the wall. I kept the header about 16" above the heater. I have had the sauna reach 110 degrees. Way too hot, but my kids wanted to see what temperatures they could take. Good luck and if you have more questions feel free to contact me.

Thank you, now its all clear! I found this type of construcion.

Awesome!!! Clever skilled you..and what a lovely story behind it including your wife’s childhood and the birdcam too!! Amazing.