Sauna construction grows from the ground up.

Sauna construction that starts with a solid and stable foundation is one key to a long lasting outdoor sauna. The purpose of a foundation is permanence and stability. The idea is to use non- deteriorating materials that are connected to the ground in a way that won’t shift, even when the ground heaves from frost in cold climates.

Of course the foundation of an indoor sauna can be the existing floor.

sauna foundation pic

LOCAL CODES

Local building codes dictate requirements if your sauna is going to be inspected.
Even if there won’t be an inspection local codes are a good guideline to use.
As annoying as codes may seem at the time of construction, they have been developed to suite local conditions and have the consumer (YOU) in mind. They are designed to produce a quality, long lasting and safe building. In the long run they should be followed even if you could “get away with” shortcuts.

If you are unsure about codes, call your local building inspectors office. Many of them have quick reference booklets.

FOOTINGS

If you live in a warm climate the foundation may be as simple as a 12 deep block pier or railroad ties on a sand/gravel layer.
Colder climates require deeper footings. In my area of Michigan footings need to be at least 48 inches below grade.
This may seem to be excessive for small building but remember that small buildings shift more easily than larger ones when the ground moves.
In any case, you are going to put a fair bit of sweat equity into your sauna construction so you might as well make sure it will stay put.
FLOORS

Rob Roy’s book The Sauna Book is an invaluable resource for the entire building process. He is a big advocate of cordwood masonry. In addition to covering the complete sauna construction process he clearly illustrates FLOATING SLABS, RAILROAD TIE and POST style foundations.
If you pour a concrete foundation, think about sloping it for drainage.
If you use a wood frame floor it should drain and/or be well sealed with ventilation undreneath to avoid rot.

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