Moisture in Saunas: What to Expect and How to Prevent Problems

Your sauna is designed to be a warm, dry, and relaxing escape. However because saunas are built from natural, untreated wood, it is normal to notice some degree of moisture or dampness during and after use. Wood naturally absorbs and releases water as it heats and cools, and over time this can show up as dark patches, minor swelling, or condensation.

The key is understanding the difference between normal moisture behaviour and signs of a problem that need attention. Here is what you can expect, what to watch out for, and how to keep your sauna in excellent condition.

Why Moisture Appears in Saunas

Several factors can contribute to visible moisture in and around your sauna:

• Natural wood behaviour - Untreated timber expands, contracts, and releases moisture with temperature changes. This is normal and expected.
  
  
• Condensation - Steam and humidity may collect on walls, ceilings, glass, or under flooring, especially if ventilation is limited.
  
  
• Groundwater or poor drainage - Outdoor saunas built on soil, decking, or uneven foundations can draw in water during heavy rainfall.
  
  
• Leaks from nearby structures - Water from gutters, roofs, or garden buildings can travel into the sauna if not properly managed.
  
  
• Improper sealing - Gaps in flooring, wall joints, or around doors may let external water in or trap moisture inside.
  
  

What’s Normal Moisture vs. a Problem?

Normal and Expected:

• Temporary damp patches after sauna use
• Wood panels darkening where exposed to humidity
• Minor swelling of timber that settles once dried
• Condensation on glass or fittings

Signs of a Problem:

• Persistent standing water on floors
• Strong musty odours or visible mould
• Warping or long-term damage to panels
• Reduced heating efficiency as the sauna struggles to dry out

How to Manage and Reduce Moisture

• Identify the source – Is it natural wood behaviour, condensation, or external water getting in?
  
  
• Improve drainage – For outdoor saunas, ensure water flows away from the base. Consider a concrete slab or raised decking.
  
  
• Seal key joints – Use sauna-safe sealants sparingly on flooring edges, corners, or around doors where water ingress is most likely.
  
  
• Ventilate effectively – Good airflow reduces condensation. Open vents or the sauna door after each use to let moisture escape.
  
  
• Replace damaged sections – If moisture has caused mould or rot, it may be necessary to replace panels or insulation.
  
  

Preventing Excess Moisture in Saunas

• Start with strong foundations - A solid, level, and well-drained base prevents groundwater problems.
  
  
• Allow natural drying - The wood is untreated for a reason, it needs to breathe. Avoid sealing all surfaces.
  
  
• Regular checks - Look for early signs of mould, damp, or staining during cleaning.
  
  
• Book professional servicing - An annual sauna service keeps both the structure and heater performing at their best.
  
  

Embracing the Nature of Sauna Wood

A certain level of moisture in saunas is perfectly natural due to the use of untreated wood. Rather than seeing it as a flaw, it’s part of what makes the sauna experience authentic. The key is to recognise when moisture is behaving as expected and when it signals a maintenance issue. With good ventilation, proper drainage, and regular care, you can prevent long-term problems and keep your sauna a safe, comfortable wellness retreat for years to come.

At Take Wellness, we provide expert sauna installation, servicing, and maintenance across the South West and South Wales. Whether you’re concerned about excess dampness or want guidance on keeping your sauna in top condition, our team is here to help.