Finnish Sauna





Introduction: Finnish Sauna

Since I really like sauna I have decided to make my own. I had a little bit of space in old barn next to our house, a friend who was crazy enough to help me and wife who let me do it.

I have attached a lot of photos how I did my sauna. To describe everything it would just take too much time and I think picture can tell more then 1000 words.

Step 1: Planning and Preparing

I had a vision how my sauna should look like. It has to be large enough for 2 people to lay down, it has to be comfortable enough for relaxing and has to be "perfect".

This instructable is written to cover "basic level". It's more "how it was done". To cover all the details it would take just too much time. If you have any specific question just write in the comments, I'll answer as soon as I can.

I started searching internet for wood. Ready made wood for sauna was WAY too expensive so I tried approach - get raw material and find a craftsman to wood. I have found a guy who was selling dry spruce planks for sauna walls and at the same time cheap 4cm x 2.5cm x 4m uncrafted linden wood.

So rent-a-wan it was. I rented a wan, drove 200km to get my wood and pack it together. By the low a cargo can go 1 meter out of a car - in total we had 98cm - I call that a pure luck. Wood was at home and time start.

Step 2: Floor

The barn was a concrete structure with concrete floors. Not really nice for sauna. I have decided to just put some OSB bords on floor. It looks nice and it's warm to walk on there bare foot. Boards are jut placed on the ground and glued together using wood glue.

Step 3: Shaping Linden Wood

To be able to sit on those linden planks I have asked a local craftsman to shape them. He just let the wood trough machine that made it smooth and rounded edges. See picture before / after.

Step 4: The Frame

A layout of sauna was drawn on 1 paper. Just rough dimensions of frame, doors, benches, ... Everything else was made on spot.

I have used 5x8 (cm) wooden peaces to construct the frame. On the outside of the frame I have put a foil that does not let moisture in, but it does let it out.

Step 5: Insulation

Once the frame was set up it's time for insulation. Styrofoam is not suitable for sauna insulation where temperatures can get up to 120 degree Celsius. So I used mineral wool instead. Please also note extra wood where benches attach to the wall. The insulation is 8cm thick - the same as wood used for construction.

On the inside I used aluminum foil (not the normal kitchen one but stronger, construction one, that does not tear). I used aluminum tape to seal all overlaps together to prevent air going into insulation.

Step 6: Walls

Walls are covered in spruce planks. I got planks with grooves, so planks just slid one into another. I used small metallic holders to keep planks in place. In corners I have left about 1cm of space so wood can "breathe". The 1 cm gap is hidden by the plank of neighboring wall.

Step 7: Roof

The roof if made the same way as walls. Aluminum foil, 5x8 cm frame, 8cm insulation between frame and I have added another 20cm of extra insulation on top. One way foin on top, to prevent moist air getting into insulation.

Extra think is went hole on top. Air has to circle around sauna. On top there has to be went hole and under furnace intake air hole.

Step 8: Electrical Wiring

Electricity in sauna is used for lighting, sensor and heating. I used silicone cables so cables can stand 120+ Celsius of heat.

I have cables for 2 lights (on picture), temperature sensor, lights under benches and electric heater. All the cables are connected to electric box outside of sauna.

Step 9: Doors

Doors uses the same principle as walls and roof. Except somewhere in between there is small triple glass window

Step 10: Benches - Frame

Frame of benches is made from same wood as the rest of the frame. 5x8 cm. There was no special calculation how strong shall it be. Me and my friend (both over 100kg) used our own weight to sit on the frame and when there was no movement and squeeching we sad it was "OK". We used 6x110mm screws to fix the frame into walls.

Step 11: Benches - Sitting Space

Since I used B-grade linden wood there was a lot on impurities in it. I was not able to find enough long enough pieces to make benches, so I decided to turn this wood for 90 degrees. I needed much more wood, but shorter pieces.

Each 40-60cm and 2.5x4cm is screwed from below on 3x3cm spruce piece of wood. To prevent this tiny wood from cracking I drilled a hole for the screw. We just have to be careful the screw does not come all the way trough.

Step 12: Electric Heater

The stove itself has to be powerful enough to heat up sauna to high temperatures. It's recommended for every 1 to 1.25 cubic meter of air there is 1kW of power.

Mine is 9kW, 3phase, 400V heater and I got my second hand. That way I was not able to choose power rating directly, but it does it's job. On top of the heater you need to put stones where you can pour water to control humidity. Stones need to be special for sauna to withstand heat and water at the same time. I got them for 22€ in local shop.

Step 13: Final Touches

I added lightning (salt lamps), rubber sealing around doors, handles for doors, thermometer, connected electrical wiring, made a small hatch for went hole, ...

Sauna is operational for about a year now. My family likes it, we use it about 2 times a week during winter. I did some mistakes of using B-grade wood as some cracks formed in wood next to heater and on the walls.

Machines used for making this was a table saw - Metabo ts 254, mitre saw - Metabo ks 216, Metabo FMS 200 grinder, a cheap battery drill.

The total costs for everything - wood, foils, screws, electrical wiring - was about 550 EUR in 2015.

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26 Discussions

can i safely use a different type of control panel, instead of the fancy one offered? i was thinking a timer system. could you recommend one that will work. thanks in advance.

1 more answer

Timer system, as you described, might not be as good as you think. I am preparing another instructable to make a digital sauna controller, however it's not ready. For this sauna size you could basically just use regular switch, as temperature is really stable after you get to 80°C. It takes roughly 15 minutes for 5° difference. With switch you can just turn it on, go inside for 10-15 minutes, come out ans switch it off. Just before re-entering you switch it back on. After couple of usages you will master the timing. My "fancy controller" made with raspberry pi died due to SD card failure and I was controlling my sauna like I described for months.


1 year ago

One thing you could do instead of drilling holes for the screws to avoid cracking is get some self tapping screws.

Congratulations on your first Instructable! The sauna looks great. What makes it "Finnish"? Is it the style or how it is heated? I don't know anything about saunas or Finland!

7 replies

Hey. Traditional Finnish sauna is dry and hot (humidity less than 20%, temperatures ranging between 60 - 120 Celsius (140 - 250F) with average between 80-100. It's traditionally heated up with wood, but now-days electrical heater is used.
Other types are Turkish sauna (or Turkish bath) where temperatures are between 40-60 with 100% humidity (fog).
You can have Infrared sauna, that uses infrared heaters to heat your body and not directly air around you. This type is the cheapest one and you can get them for like 1000€ in supermarkets.
Smoke sauna is rarely used today, but it's the wood burning Finnish sauna without chimney.
I selected this dry and hot with electric heater cause it's the preferred sauna type of me and my wife.

A real Finnish sauna is anything but dry. "Löyly" (steam from throwing water on the stove) is the most important thing in our saunas, temperature is in the 75 °C - 120 °C range and humidity well above 80 %.

Greetings from Finland!

This is something I am getting hard to believe. At 80°C and 80% humidity you need approx. 0.5l of water per 1m^3 of air in sauna. That is 4 liters of water for my sauna - not counting any humid air that goes out trough vent-hole. At 120°C you need almost 5 liters of water per 1 cubic meter of air to keep 80% humidity. If that is true and you do take 50 - 100l of water to sauna and pour it on stones that's fine, but at the same time I would like to see that.

My sauna bucket holds approx. 12 liters of water and we use that much of water trough the sauna session. That way we keep humidity up to 30%, normally about 20%.

You are indeed correct. I'm confusing absolute with relative humidity, 80 g water/kg air at 80 °C. That is also a tad high according to the Finnish wikipedia about the sauna, but that is what I've been told.

80g/kg is 13% humidity at 80°C. This is still dry, compare to Turkish 100% fog. But yes. Adding water helps regulate humidity in air.

Awesome `ible!

There is also a Russian sauna which is basically a smoke sauna but with a chimney. I own one and it is my absolute favourite. I find that Finnish saunas mostly "grill" you from the outside (with the 90 celsius) , but the Russain sauna really gets to your bones (only 60 celsius) so you feel super relaxed afterwards.

Nevertheless, sauna is an awesome invention and I could not go a week without it!

Greetings from Estonia!

Hi. Looks nice.

But I live in Finland and don't like the dry saunas. We always put water on the stones on the oven to get the air more "wet". Feels better. This looks more like the one they build in Sweden. :D

But that is only my opinion. ;)

My wife is from Finland. I will be building my 4th Finnish sauna in my new house next year. Nice work here :)

2 replies

Do you have any pictures to compare?

The first 3 pictures was a basement sauna in my second house the last is a sauna in my outdoor garden shed. Sorry not many pictures of actual build.


1 year ago

after sauna have best feeling newer, fresh and clean feel, i have sauna at thailand, thailand have hot weather but if warm sauna and go in and then shower have wery fresh and good feel and not have hot :) shower or bath not can newer make same good feel, or steam sauna or new stupid infrared sauna.


1 year ago

I hope that you held the minimum required clearance between your thermal reflective barrier and any other surfaces. You need a 1/4 to 1/2 inch air gap minimum for reflective barriers.

With several layers of reflective barrier one does not need mass insulation, this reduces the heat up time of the sauna.

The cost of say 4 layers of thermal barrier is the same as one of mass insulation!

I Hope this helps.

1 reply

This is something I didn't know. Reflective barrier is just under inside spruce planks, but primary job is to keep moisture in.

Thanks for sharing your great job !

I want to build one but first i want to ask at experts like you why finnish sauna is better than infrared. I can't see a good answer, googling on internet.

I prefer the finnish sauna...

By the way, great job man! ;)

1 reply

I prefer the Finnish sauna... would be the answer. I don't know.

Finnish sauna has hot air that makes you sweat. Usually 60 Celsius +

Infrared has infrared heaters, that heats you directly and not air. Air temperature is about 40, but you still sweat. However there is no stones to put water on them, to regulate humidity, there is no "let's make hell temperature" as you can't. However it does consume less power.

Great work! Looking good! You haven't had any problems with spruce blanks? Here in Finland we try to avoid pine trees in sauna because it might sweat some resin when warmed. Aspen is the best wood for sauna (at least for benches). Very important thing is the ventilation! Air in in bottom level of stove and out through ceiling. More information about Finnish sauna: Yours JK