How to Build a Sauna in a Shed

How to Build a Sauna in a Shed
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So, you have a shed, and you’d rather have a sauna. We’re going to go through a step-by-step process on how to build a sauna in a shed. You don’t have to hire a professional to build a sauna from scratch for thousands of dollars, and you don’t really have to build one from scratch either.

If you have a pre-existing shed that you don’t need anymore, with some ingenuity, a bit of hard work, and a few key materials, you can turn it into your own awesome little sweat lodge.

The Insulation

You will need to add a great deal of insulation to the walls of the existing shed to make sure that as much heat stays inside as possible, as this is of course the whole point of a sauna. Here, you should use rolled fiberglass insulation.

Pay attention to the “R” value of the insulation. You should use R13 insulation for the walls and R26 insulation for the ceiling. Moreover, will want to double up on the insulation layer, running one layer perpendicular to the other. Simply attach this insulation to the interior of the existing shed wall.

The Moisture Barrier

The next step is to create a moisture barrier, especially if you are making a Finnish sauna which involves a lot of moisture and steam. You can buy some fairly expensive professional moisture barriers from a local home improvement store. However, if you want to save some money, you can go for some very large and heavy duty aluminum foil.

To create a proper moisture barrier, you may want to double or even triple layer the foil. Ensure that the shiny part of the foil faces the inside of the sauna/shed to keep in as much heat as possible. You can choose to attach it any way you see fit, but whatever you do, ensure that the attachment method is waterproof, so moisture doesn’t loosen it and cause the foil to come off.

Cedar Wall Boards

The next step in turning your old shed into a new sauna is to install cedar wall boards. Cedar is generally the best option. Now, cedar planks are not cheap, so if you can, go find some unfinished ones which you can finish yourself.

The best way is to create tongues and grooves on each board which will overlap with each other, thus creating a fairly solid seal. You can also go with a simple ship lap design, which means cutting an “L” shape into each board, so they overlap with each other. Mount these boards over the moisture barrier, which is mounted over the insulation.

The Door, Floor, and Ceiling

Realistically, if you have an old shed, you will need to repeat these previous three steps for the door, the ceiling, and the floors too. All surfaces should feature a double layer of insulation, followed by the moisture barrier, and then the cedar planks. This needs to be done to keep as much heat and moisture inside the sauna as possible.

How to Build a Sauna in a Shed

A Wood Burning Sauna Stove

Next, you will need to install the stove, the thing that will provide you with the heat for your sauna. Ideally, you will want to cover the wall closest to the stove with a cement board and paving bricks to protect the wooden wall from damage and from possibly setting it on fire.

You will then need to run the stove pipe through the wall, at the same level as the top of the stove, and to the exterior of the sauna. Be sure to get a double wall pipe, so the amount of heat transfer is minimal. You don’t want a super-hot metal pipe being in direct contact with the wood. Any material in the wall that is not fireproof should be removed (where you run the pipe through).

Be sure to check local regulations in regard to the size of the stove and the distance of the stove from wood walls, just for safety and legal reasons. Now, to calculate the number of BTUs the wood stove should produce for an effective sauna, you will want to use a simple BTU calculator that can be found by searching online.


On a side note, you will want to incorporate some sort of small vent into the roof, just to allow some air to get out and some fresh air to get in.


There you have it — how to transform a pre-existing shed quickly, easily, and cost-effectively into a pretty awesome sauna. If you do it right, it’s something you will be able to enjoy for years to come.