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.