Sauna Drainage: Where Does All That Water Go?

Sauna Drainage: Where Does All That Water Go?

Between pouring water on the rocks, heavy sweating, and occasional cleaning with a hose, saunas deal with a surprising amount of water. Getting drainage right prevents moisture damage, mold, and premature rot. The approach depends on whether your sauna is indoors or outdoors.

Indoor Sauna Drainage

Indoor saunas built in a converted bathroom or basement often have access to existing floor drains. If you're building in a space without a drain, you have a few options:

• Sloped floor to a drain: The best solution. Slope the floor slightly (1/8 inch per foot is enough) toward a floor drain connected to your home's drain system.
• Sealed floor with no drain: Many indoor sauna users simply towel off the benches and floor after each session. If you're not dumping buckets of water on the rocks, the moisture is mostly sweat that evaporates once the door opens.
• Waterproof membrane: If no drain is available, a waterproof membrane under tile flooring contains any water that does accumulate, preventing damage to subfloor materials.

Outdoor Sauna Drainage

Outdoor saunas have it easier in some ways because water can drain directly to the ground. But you still need to manage it:

Under the Sauna

If your sauna sits on a gravel pad, water that drips through the floor boards percolates into the gravel and disperses naturally. This is one of the biggest advantages of a gravel foundation.

If your sauna sits on a solid concrete pad, the pad should have a slight slope (1-2%) away from the sauna's center so water doesn't pool underneath.

Around the Sauna

Grade the ground around your sauna so it slopes away from the foundation. You want rainwater running away from the structure, not toward it. A minimum 1-inch drop per foot for the first 4-6 feet around the sauna is a good target.

Roof Runoff

Don't ignore where roof runoff goes. Without gutters, rain pours directly off the roof edge and can erode the ground around your foundation. Gutters with downspouts directed away from the sauna, or a drip edge with a gravel splash pad below, solve this.

Floor Materials That Help

Inside the sauna, your floor should be a material that handles water without damage:

• Concrete (sealed or unsealed)
• Tile with waterproof membrane
• Duckboard (removable wood slat floor) over concrete or tile
• Vinyl or composite for easy cleaning

Avoid carpet, laminate, or unsealed wood flooring. They trap moisture and become breeding grounds for mold.

Related Terms

• Sauna Foundation Options
• Gravel Pad for Saunas
• Preventing Mold in Saunas
• How to Clean a Sauna

Set Up Your Sauna Right

Good drainage starts with the right foundation. Browse our outdoor saunas and check the installation guides for each model's specific drainage recommendations.