ᐅ Basement sauna: what should be considered?

Hello everyone,

After finishing my bathroom project, the next one is coming up... a sauna needs to be installed in the basement. :-)

The sauna has already been purchased; it is a 2.1 x 2.1 m (7 x 7 ft) cabin with walls and ceiling built in a sandwich construction (wood frame, insulation in between, and cladded on both sides with profiled boards).

We have chosen our currently unused basement room (just under 30 m² (320 sq ft)) as the location. The room offers enough space for the sauna, a few loungers, and possibly a shower which I might install later. The basement room is unfortunately unheated (except for a wood-burning stove), and here my main concern begins... warm moist air + cold walls = condensation.

Here are a few additional details about the room:
- As already mentioned, the room is just under 30 m² (320 sq ft) with no radiators installed. The ceiling height is 2.20 m (7.2 ft).
- The floor is tiled; I would like to install a high-quality click vinyl floor over it, as I think this would be much more comfortable than the cold tiles.
- The walls are plastered and painted.
- The room has a small basement window that can be tilted open (30 x 60 cm (12 x 24 inches)).
- There is a core drilled hole in the chimney for installing a wood-burning stove.

Here are some details about the sauna:
- External dimensions 2.1 x 2.1 m (7 x 7 ft), 2.05 m (6.7 ft) high
- 9 kW stove with sauna and steam bath functionality (a type of steam room with relatively high humidity of about 50–60%)
- Sandwich construction

My questions are as follows:
I plan to leave a 10 cm (4 inch) gap all around between the sauna and the outer walls to allow air circulation. Should I additionally install a fan or something similar to ensure actual air circulation?
Do I need to insulate the exterior walls in any way?
To remove the warm and moist air from the sauna room, I was thinking of installing a timer-controlled extractor fan (mounted in the window) that runs for a certain time after sauna use.
Additionally, I would place an electronic dehumidifier in the room to sustainably maintain a low humidity level.

I plan to start the wood stove 2–3 hours before using the sauna so the walls can warm up a bit. The stove has a 120 kg (265 lb) heat storage mass, meaning it stores heat for several hours and cools down gradually; therefore, the room temperature will also decrease slowly, which I believe is advantageous.

What do you think of my plan?
What would you recommend, what did I forget, and where am I completely wrong?

Thanks in advance

You’ve already thought of everything.
If the sauna room is open to the other rooms in the basement, the heated air spreads quite quickly throughout the basement.
This means your mirror, or anything else, will fog up when you open the sauna and then dry again within about 10 minutes.
More moisture forms in the air when showering than when using the sauna.
The distance from the exterior walls is important. Air circulation happens naturally. For safety, check visually from time to time.
If there isn’t an insulated plastic window installed, leave it slightly open after sauna use to prevent condensation.
A wood stove in the sauna area is highly recommended. You tend to cool down quite quickly.

Actually, when determining property tax, you’re supposed to declare that you have a sauna. This increases the property tax. However, many people forget to do this for some reason.

AOLNCM schrieb:
You’ve already thought of everything.
If the sauna room is open to the other rooms in the basement, the heated air spreads quite quickly throughout the basement.
That means your mirror, or whatever else, will fog up when you open the sauna, but after about 10 minutes everything is dry again.
Showering creates more humidity in the air than using the sauna.
The distance to the exterior walls is important. Air circulation happens naturally. For safety, occasional visual checks are recommended.
If you don’t have an insulated plastic window installed, keep it slightly open after using the sauna to prevent condensation.
A wood-burning stove in the sauna area is highly recommended. You do cool down quite quickly.

Technically, when calculating property tax, you have to declare if you have a sauna. The property tax is higher because of it. Many people forget this, for one reason or another.

Thank you for your reply.
I was actually unaware of the property tax aspect... I’ll have to do some research on this topic.

May I ask where you ordered your sauna from? The dimensions would also fit quite well in our basement.

Similar conditions here, but with a radiator in the room.

roadrun87 schrieb:
May I ask where you ordered your sauna? The dimensions would also fit quite well in our basement.

Similar conditions, though with a radiator in the room.

Hello,

It is a Klafs sauna.
I got it as an unused showroom model for a fraction of the original price. It was a custom-made sauna, not an off-the-shelf product... I was lucky that the size fit perfectly in my basement.