A good foundation is crucial for the stability, longevity and safe use of an outdoor sauna. Although it does not require complicated foundation work, the base must meet some basic requirements to ensure that the structure stands steady all year round. Here you will find clear and practical guidance that suits all types of saunas.

Why foundation is important

A sauna often weighs between 700 and 2000 kg depending on size and material choice. Weight combined with thermal expansion means that the construction must be level and stable.
A faulty foundation can cause:

• crooked doors and leaks

• water intrusion

• reduced lifespan of wood and frame

• unnecessary wear and tear on the supporting structure

Therefore, the foundation is always as important as the sauna itself.

Foundation requirements for outdoor saunas

To ensure a stable and safe location, the foundation should always meet these points:

1. The substrate must be level

This is the most important thing. A deviation of just a few millimeters can, over time, cause uneven loading in the frame.

2. No contact with soil or vegetation

The sauna must never be placed directly on grass, soil, bark or other organic material.
This creates moisture, rot and instability.

3. The foundation must be stable over time

The substrate must withstand both:

• heavy point load

• moisture

• frost heave

If the sauna is placed on a moving surface, both the tightness and construction will deteriorate.

4. Must have ventilation under the floor

There should be a gap between the floor frame and the substrate so that the wood stays dry.

Recommended foundation solutions

All of the solutions below work well in the Norwegian climate:

1. Concrete slabs

This is the most common and simplest solution.
4–8 large slabs are leveled and form a solid point foundation.

Advantages: Fast, affordable, very stable.

2. Compressed gravel with beams

The masses are compacted hard, and beams or adjustable plinths are placed on top.

Advantages: Good drainage, flexible on hilly plots.

3. Terrace or leveled paving

The sauna can stand upright on a slab if it is dimensioned for a high load and has not failed.

Advantages: Perfect for gardens and cottages with existing paving.

4. Cast plate

Usually not necessary, but provides extreme stability when the ground is difficult.

Advantages: Best solution for areas prone to frost or soft ground.

Can the sauna stand on beams above the ground?

Yes. A sauna can stand perfectly well on beams or a raised foundation, even where the terrain is uneven or where there is water underneath (e.g. pier, riverbank or elevated platform).
The important thing is that:

• the support points are fixed

• the beams do not move

• everything is 100% level

• the wood does not have direct contact with moisture

This is a very common solution in Norway.

Summary

To ensure long life and stability, the foundation should:

• to be completely level

• stand on non-organic material

• have ventilation under the floor frame

• withstand heavy loads without moving

• do not stand directly on soil or vegetation

With the right foundation, you get a sauna that stays stable and tight – no matter the season.

If you have any questions about sauna foundations, just contact us at post@northsuana.no!