Troubleshooting Condensation Problems:

High Interior Relative Humidity:

Excessively high interior relative humidity equates to high interior vapor pressure and is often the cause of condensation problems.  High interior relative humidity can be a function of the building’s end use, HVAC system, or improper construction practices.  Human respiration and perspiration can also contribute to a significant amount of moisture in the buildings environment.   Other common sources of indoor moisture include:

• Combustion

Oil and gas fired heaters give off a significant amount of moisture to the air.  Water vapor introduced to the air through combustion is sometimes very difficult to detect because hot exhaust gasses can hold large quantities of moisture. As exhaust gasses cool, condensation can form on cold exterior surfaces.  To avoid this situation, flue gases should always be vented outside.

• Excavated Earth

Significant amounts of moisture can be introduced into a building before it is completed.  As damp soil within the building is excavated, moisture will likely evaporate.  If the building is enclosed, this moisture will become trapped within the structure and elevate the relative humidity within the structure.  As soon as the temperature drops below the dewpoint of that air/water mixture, condensation will form.  NOTE:  The higher the relative humidity, the higher the dewpoint temperature.

• Concrete

Fresh concrete is another large source of moisture within a building.  A 100,000 ft² freshly poured 4”concrete slab has the potential to give off approximately 24,000 gallons of water into the building.   When concrete is poured after the building has been enclosed, proper ventilation is critical to remove the excess moisture vapor. Ventilation should always be considered as a preventive measure during the construction schedule. 

Types of Condensation and How to Control It:

• Visible Condensation

Visible condensation is evident when water appears on cool surfaces; it can be clearly seen.  This type of condensation can form on windows, purlins or exposed exterior fasteners.  While a nuisance, this type of condensation is far less damaging than hidden condensation.  It can be controlled by adding insulation, proper ventilation and by reducing relative humidity levels.