Relative Humidity: De-Mystified

Gym’s are used for many events that require large spaces and often enough involve athletes huffing and puffing around the floor. This much action causes your gym floors to react. Not only do gym floors react to game-time abuse, they react to fluctuations in the room temperature. Hardwood gym floors are sensitive. The more activity in the gym, the higher the temp. More specifically, the harder your team works to take the ‘W’, the higher the gym floor relative humidity.

In this post we want to take a moment to define relative humidity: the moisture in the air that affects hardwood flooring.  We will discuss relative humidity and its effects on maple flooring, and how to control it.

Ideal Relative Humidity

Go search for the term  ‘gym floor relative humidity’ and you will see a plethora of articles all quoting the might Maple Flooring Manufacturers Association:

The Maple Flooring Manufacturers Association (MFMA) recommends maintaining indoor relative humidities between 35 percent and 50 percent, and air temperatures between 55 degrees and 75 degrees year-round.

It’s commonly acceptable for hardwood gym floors to fluctuate 15% in humidity levels. However, your floors can start to show damage if the relative humidity goes outside of this margin. Signs of compromised wood flooring can look similar to the affects of water damage.  However, low-humidity levels can cause damage too.  Let’s review signs that humidity levels are above or below this 15% threshold.

High Gym Floor Relative Humidity Levels

If there is too much moisture in the air (high relative humidity) your maple flooring will react in a number of ways: 

  • Cupping: The edges of a wood plank become higher than its center.
  • Crowning: The opposite of cupping, floors crown when the center of the plank rises above the edges and creates a wave in the floor.
  • Cracking: High humidity causes the gym floor boards to expand. By doing so the boards push against themselves and cracks appear.
  • Buckling: Eventually the expanding boards run out of room and if not already cracking, they will buckle up wards separating from the sub-floor.
relative humidity levels cupping
Cupping occurs with high-humidity levels.
buckling water damage
An example of extreme buckling.

Low Gym Floor Relative Humidity Levels

Low relative humidity that’s too low causes problems too:

  • Splitting: Maple flooring used in sports floors dries out when the relative humidity is low. The dry flooring then becomes brittle and splinters. Splintered wood becomes dangerous and most likely chips away at your gym floor finish.
  • Gapping: Additionally wood floors experiencing low relative humidity shrink and leave dangerous gaps between the boards. 

It should be noted here that it is common to see installed gaps approximately every 6-8 boards.  These coin-thick expansion gaps allow the floor to accommodate occasional expansion when humidity levels fluctuate.  

gapping from low relative humidity
Boards between to separate and 'gap' as low humidity shrinks the boards.

Controlling Gym Floor Relative Humidity

Controlling relative humidity levels between 35% and 50% is a tedious task. By doing so, however, one can maintain a safe and long-lasting sports floor for athletes.  Quality Hardwood Floors, Inc. recommends these following tips to maintain appropriate humidity levels.

Maintain HVAC Equipment

We know, we’re a bit repetitive here, but you need to ensure your HVAC system is running efficiently. This is the most effective way to ensure you control humidity levels. This is also the most common root cause of humidity issues the QHF team sees. It’s a hard argument to keep the systems running all the time especially when not in use during summer months.  Our answer: it’s far more costly not to run your HVAC regularly.  Remember to maintain indoor air-temperatures between 55 degrees and 75 degrees year-round. 

In gym facilities that do not have HVAC systems, gym managers can use circulating / venting fans.  Many older gyms, without HVAC systems, may vent windows or hallway doors to circulate air. 


Dan Heney, Executive Director of MFMA suggests that sunlight should not be visible when exterior doors are closed.  It’s important to ensure proper weather seals are in place on exterior windows and doors. 

Regularly Inspect Water Sources

Again, this is repetitive but necessary: inspect your gym floor for leaks or pooling water daily. If your facility has connected locker rooms, water fountains, etc, it’s important to make sure they are no leaks. 

Commercial Dehumidifiers

If you are located in the south east of the US, chances are you battle high humidity levels. Some gyms employ the use of commercial dehumidifiers to help control humidity levels.  The QHF team has seen many third-coast gyms use commercial dehumidifiers.

Measure, Measure, Measure...

It’s important for facility maintenance to be able to measure where the relative humidity levels are.  Here’s a list of reliable data-loggers we have seen gym management crews use to ensure they are maintaining proper humidity levels.

onset hobo relative humidity reader
This OnSet HOBO Data Logger reads an acceptable relative humidity level between 35% and 50%.

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2 comments for this post
  1. […] expands when exposed to water and high levels of humidity and the moisture content of wood increases.  This causes the wood to become wider and possibly cup […]

  2. […] As we mentioned above, it is important to maintain HVAC and plumbing systems to ensure they can hold up to winter conditions. The common thought is to turn up the heat in facilities to combat wet wintery weather.  Doing so can dry out and crack your hardwood floors. Thus, it’s important to maintain gym temperatures between 60-70 degrees and humidity ratios between 35%-50%. […]