Outdoor sauna winter maintenance

Outdoor saunas are built for winter. What damages them is not the cold — it is water that gets in and then freezes, and water that sits somewhere it should have drained from. Both are preventable in about ten minutes, twice a year.

Before the first hard freeze

1. 1Empty and store the bucket and ladle indoors. Water left in a bucket freezes, expands and splits the liner. This is the single most common winter casualty and the easiest to avoid.
2. 2Drain any plumbed water completely. Anything holding standing water will split. If there is a trap, empty it.
3. 3Check the floor drains rather than pools. Water pooling on a sauna floor and freezing is how floorboards lift.
4. 4Inspect the roof covering. Any lifted shingle or torn membrane lets water into the crown, and the crown is where barrels fail. Fix it now, not in March.
5. 5Clear the base. Leaves and debris packed against the bottom of the structure hold moisture against the timber all winter.
6. 6Tighten the bands if it is a barrel. Do it before the timber contracts in the cold rather than after.

During the winter

• Clear snow off the roof if it builds up substantially. Wet snow is heavy, and it is a load the structure was not designed to carry indefinitely.
• Keep the door path clear. Ice at the threshold is both a hazard and a way to end up forcing a door that is frozen shut, which damages the frame.
• Do not force a frozen door. Let it thaw. Forcing it racks the frame, and a door that no longer seals is a permanent heat loss.
• Run it. A sauna used through winter dries itself out regularly, which is better for the timber than sitting damp and unused for four months.

After each winter session

Leave the door ajar for a while so the interior dries rather than sitting warm and damp with the door shut. This is the single most useful habit for the timber, and it costs nothing. Wipe the benches down while the room is still warm — sweat and mineral residue come off far more easily then.

In spring

1. 1Full visual inspection. Walk around it. Look for lifted shingles, split staves, movement at the base, and any timber that has stayed dark and damp.
2. 2Check level. Frost heave moves things unevenly over a winter. If it has racked, deal with it now — a racked structure means a door that will not seal.
3. 3Tighten the bands again. Timber that contracted in the cold will have expanded back.
4. 4Bring the bucket back and check the liner survived storage.
5. 5Consider the exterior finish. Cedar silvers with UV, which is cosmetic. If you want to keep the color, spring is the time for a UV-protective exterior finish — never the interior.
6. 6Turn out the stones if it is a traditional heater. Cracked and crumbled stones restrict airflow, which makes the elements run hotter and shortens their life.

What not to do

• Never seal or varnish the interior. Bare timber breathes and releases moisture; sealed timber traps it and gets unpleasantly hot to touch.
• Do not pressure-wash a sauna. Forcing water into stave joints and end grain is the opposite of what you want.
• Do not use household cleaners inside. Residue vaporizes at temperature. Water and a brush, or a cleaner specified for saunas.
• Do not wrap it in a tarp for the winter. A sealed cover traps moisture against the timber, which is worse than the weather it is keeping off.

The stones are a consumable

Worth repeating because it is routinely ignored: sauna stones crack and crumble with thermal cycling, and degraded stones restrict airflow through the heater. That makes the elements run hotter and shortens the heater's life. Manufacturers generally advise inspecting them at least annually — check your own heater's manual, since the recommendation varies by model. Sauna stones guide covers what to buy and how to turn them out.

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