How to build a Sauna Floor

Sauna floor should be durable, waterproof and warm.

Durable, because we like to stand on a firm ground. Floor made with plywood that is too thin, insulated with Styrofoam and on beams which are spaced too far apart, is a recipe for a disaster. Such floor will last a couple of months of use after which it will start to deform.

Waterproof, because in a sauna it is not uncommon to spill water on the floor. When we pour water on top of the heater stones, it may happen that not all of the water will evaporate and some of it will drip on the floor. In such case, the floor should be waterproof not to let water through. This is of course only in saunas inside of a building.

Warm, because it is one of the elements that keep the heat in. In a typical garden sauna, the floor is responsible for about 10% of heat loss. In the long term a good insulation pays off, especially if we use an electric heater.

To answer the basic question : “How to build a sauna floor?” we have prepared two answers that address it, one for internal sauna and one for external garden sauna.

Sauna Floor in Internal Sauna

If the sauna is inside of a basement or adjacent to a bathroom, the choice of floor type is simple. Best solution is to use ceramic tiles. There are thousands of shapes, colours and type to choose from. They are extremely durable and waterproof. The floor on which we put the tiles on should be insulated, preferably with XPS insulation.

Below is an example of sauna floor layers in a building:

1. Ceramic tiles
2. Elastic tile adhesive
3. Waterproof layer
4. Concrete floor.
5. XPS insulation

Floor in an external sauna

If your sauna will be located outside, there are more things to consider. In case of timber frame building, the floor should be insulated with mineral wool (ie. RockWool) or special insulating panel from Kingspan - sauna - satu. As a subfloor we can use a sheet of OSB that sits on top of the floor joists. The OSB that are used in sauna construction should be free from formaldehyde, so make sure that the boards you buy meet the most recent requirements. In our sauna Tuula prototype, we have also used a fiber-cement board. On top of the OSB we have poured a thin concrete slab. The thickness of t he slab can be from 10mm to 40mm (1/4in to 1in). For the floor to be waterproof, you have to seal the concrete with a floor epoxy. It is simply painted on with a paint roller.

Below is an example of external sauna floor layers:

1. Waterproof epoxy floor paint
2. Thin concrete slab
3. Waterproofing layer
4. OSB board
5. Thermal insulation in floor joists.

Do you have a different way in which you build your sauna floor? Let us know in the comments below.