How Does Humidity Affect Buildings

When it comes to your heating, ventilation, air conditioning (HVAC) system your main focus may be temperature control, but humidity control is equally, if not more, critical. A facility’s air humidity levels affect the people inside and the building itself.

How does humidity affect buildings and why is it important?

High Humidity levels can cause extensive damage to buildings and create an unhealthy environment for occupants.

According to the Environmental Protection Agency (EPA), too much moisture in a building can cause significant damage including:

  • Mold, bacteria, wood-decaying molds, and insect pests, like termites and carpenter ants.
  • Corrosion of building components, including structural fasteners, wiring, metal roofing, flooring adhesives, and roofing adhesives.
  • Water-soluble building materials returning to solution.
  • Warping, swelling, or rotting of wooden materials.
  • Damage to brick or concrete during freeze thaw cycles and by sub-surface salt deposition.
  • Damage to paint and varnishes.
  • Reduction of thermal insulation insulating value (R-value).

A building’s air humidity level can play a huge role in the transmission of airborne viruses and droplets.

A study by the U.S. Institute of Medicine Committee on Damp Indoor Spaces and Health found an association between exposure to damp indoor environments and detrimental health effects including:

  • Upper respiratory symptoms
  • Cough
  • Wheeze
  • Asthma symptoms in people with asthma

Excessive dryness in a building also causes the same issues: building damage and health problems. Low humidity causes wood to crack and increases the possibility for electrostatic discharges, which is an unsafe environment to have near electrical components. Allergies and illnesses are easier to catch in a low humidity environment because small particles can stay airborne for longer amounts of time in low humidity levels.

What is the purpose of humidity control in buildings?

Humidity control helps extend the life of buildings and keeps employees within facilities healthier and more comfortable. Controlling the moisture and dryness of levels of a facility can fight off mold and corrosion and protect your employees from adverse health effects.

What is the ideal indoor relative humidity level for commercial buildings?

According to The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) you should consider maintaining the indoor relative humidity (RH) of your facility at 40-60%. defines relative humidity as, “the amount of water vapor present in air expressed as a percentage of the amount needed for saturation at the same temperature.”

Why is 40-60% the magic range?

Dry air below the suggested minimum of 40% has been shown to reduce health immune system function, increase transmission of some airborne viruses and droplets, increase the survival rate of pathogens, and decrease the effectiveness of hand and surface disinfection practices. Wet air above 60% increases the likelihood of allergens and causes mold and mildew. At the same time, humidity levels about 60% make the environment feel hot and sticky, which makes a working space uncomfortable for employees, thus causing decreased productivity.

ASHRAE says ways of ensuring your facility’s relative humidity level is safe include watching spaces to ensure no condensation is occurring, take note of climate-informed HVAC recommendations (which we get to further in this article), and be careful when restarting older humidifiers to ensure proper moisture absorption.

How do I lower the humidity in my commercial building?

One of the most effective ways to reduce humidity and control the moisture content in your building is by following the ASHRAE climate zone map guidelines when designing your HVAC system (more on this later). An additional method to consider is installing cost-effective high volume, low speed (HVLS) fans in your facility.

HVLS fans lower the moisture and humidity levels in a building. As added bonuses, the fans also produce better air quality and make a more comfortable environment for your employees, increasing productivity.

HVLS fans can help you maintain the ideal RH level and increase the indoor air quality in your building when paired with proper ventilation practices. If you keep the windows and doors open in your facility, HVLS fans are able to circulate the clean outdoor air throughout your facility and eliminate stagnant, unhealthy indoor air. HVLS fans also mix warmer ceiling air with cooler floor air, which increases the evaporation rate, thus reducing moisture in your building.

You can pair HVLS fans with a dehumidifier to reduce humidity and condensation even further.

Knowing Your ASHRAE Climate Zone Can Help You Maintain Your Ideal Relative Humidity Level

Research from an architectural firm, SmithGroup, finds climate-informed HVAC may fight pandemic viruses. Climate-informed HVAC involves designing an HVAC system to operate following the ASHRAE climate zone map.

There are eight ASHRAE climate zones: hot-humid, mixed-humid, hot-dry, mixed-dry, cold, very-cold, subarctic, and marine.


According to Building America, an organization that uses the ASHRAE climate zone map to help builders determine the appropriate climate for which they are building in, the hot-humid climate is a region that receives more than 20 inches of annual rainfall and where one or both of these situations occur: 1) A 67°F or higher wet bulb temperature for 3,000 or more hours during the warmest six consecutive months of the year; or 2) A 73°F or higher wet bulb temperature for 1,500 or more hours during the warmest six consecutive months of the year.


A mixed-humid area receives more than 20 inches of precipitation every year and has about 5,400 heating degree days (65°F basis) or fewer and average monthly outdoor temperatures drop below 45°F during the winter months.


A hot-dry climate is identified as a region that receives less than 20 inches of annual precipitation and the monthly average outdoor temperature remains above 45°F during the year.


A mixed-dry climate is defined as an area that receives less than 20 inches of rainfall per year and has about 5,400 heating degree days (65°F basis) or less and the average monthly outdoor temperature drops below 45°F during the winter months.


A cold climate is identified as a region with between 5,400 and 9,000 heating degree days (65°F basis).


A very cold climate is defined as a region with between 9,000 and 12,600 heating degree days (65°F basis).


A subarctic climate is defined as a region with 12,600 heating degree days (65° basis) or more. Subarctic regions are only found in Alaska.


Building America says a marine climate is defined as a region that meets all of the following criteria:

  • A coldest month mean temperature between 27°F and 65°F
  • A warmest month mean of less than 72°F
  • At least 4 months with mean temperatures higher than 50°F
  • A dry season in summer. The month with the heaviest precipitation in the cold season has at least three times as much precipitation as the month with the least precipitation in the rest of the year. The cold season is October through March in the Northern Hemisphere and April through September in the Southern Hemisphere.

As previously mentioned, scientists have found viruses cannot survive as long and cannot transmit as effectively in a building with an indoor relative humidity of 40 to 60 percent. Keeping air at the recommended RH also lends respiratory benefits and helps patients produce a more productive cough.

SmithGroup research found there are ideal windows of opportunities for maintaining certain humidity levels depending on where you live and how it falls on the ASHRAE climate zone map.

For example, in New York City, New York, the SmithGroup research finds an immediate window of opportunity for facility managers and engineers to increase humidification to 40% during the spring. Following that, humid outside air should keep indoor RH about 40%, while a building’s air conditioning system should keep the humidity below 60%.

Then, another window of opportunity happens months later. While in Miami, Florida – where, of course, the outside temperature is much more humid on average than NYC – there are fewer windows of opportunities and no humidification is needed to reach the recommended RH for most of the year.

The research has further recommendations for facility leaders wanting to keep the recommended ideal RH, including consider temporarily reducing economizer cycle operations so central humidifiers and local boosters do more, optimize control and high-limit sensors for humidifiers at air handling units, consider adding booster or local humidifiers before fall, and before winter, set RH settings down incrementally to follow weather patterns.

It should be noted SmithGroup’s research is geared towards healthcare facility leaders, but that doesn’t mean their findings don’t spill into other industries, like manufacturing, factories, office buildings, grocery stores, schools, or warehouses – anywhere where you may expect to see a large population of people.

If you’re concerned about the humidity level at your facility, contact us so we can work with you to figure out a plan that helps make your facility a healthier and more comfortable place to work for your employees. On top of that, you’ll save on energy costs and maintain the life of your building.