Reducing the risk with reflective insulation
Within metal building interiors, ceilings and wall surfaces are often prone to condensation, resulting in moisture accumulation on these surfaces. If enough water vapor condenses on the surface, it can then drip back into the building, possibly damaging contents as well as the floor below. Over time, this can also lead to mold and mildew-related issues.
To prevent interior surface condensation, it’s important to understand the various factors and conditions that cause it to happen. Poor thermal insulation and inadequate ventilation increase the likelihood of condensation problems and contribute to the conditions that make it possible.
It’s also important to know that an interior vapor barrier alone will not prevent condensation. A vapor barrier is intended to block interior moisture (humidity) from reaching the building framework, insulation materials and the metal cladding. Condensation can occur on any interior surface, including vapor barrier materials.
Three factors
Three factors contribute to the likelihood of condensation within metal buildings: warmer interior air temperature, higher interior humidity levels and cooler ceiling surface temperatures. Whenever condensation forms on ceilings or walls, it’s important to understand that this moisture originated from inside the building, not the outside. The source of this moisture is water vapor in the air within the building. The more water vapor is present, the higher the humidity. Condensation can form when water vapor in the air meets a cooler surface. If the temperature of that surface is lower than the dew point of that air, moisture in the air will change from a vapor to a liquid, and then collect on the cooler surface.
This is very similar to why the outside of a cold soda can will sweat when exposed to warmer air. When this happens, water vapor in the air condenses on the cold outside surface of the can. The greater the temperature difference between the can and the outside air, the more likely condensation will form. This is why moisture doesn’t form on the outside of a warm soda can. This is also why moisture doesn’t form on a cold can inside a refrigerator. In both of these examples, condensation is less likely because the temperature difference between the can and its surrounding air is lower.
Condensation occurs on a surface where the temperature differential is high enough between opposing sides. In metal buildings, this occurs at the ceiling and interior walls. Since warm air rises, the inside air near the ceiling is warmer. When the outside air temperature drops, the exterior surfaces then begin to cool. As a result, interior surfaces begin to cool as well. Therefore, the colder interior ceiling surface is exposed to warmer inside air, increasing the risk of condensation. If the interior ceiling surface temperature falls below the dew point temperature of the interior air, the water vapor in the air will condense on that surface.
Reduce heat gain
The first step in reducing condensation risk is to reduce heat gain inside the building. An effective thermal insulation in any metal building must provide a reflective radiant barrier. This is because virtually all of the incoming heat is radiating from the exterior metal panels. Conventional fiberglass insulation is intended to hold heat (which is measured by Rvalue), but does very little to stop radiant heat flow into metal buildings. Reflective insulation is usually composed of a polymer bubble substrate bonded with an aluminized radiant barrier.
Installed properly, a reflective insulation will reflect, or redirect, radiating heat energy away from the building’s interior. This will dramatically reduce heat gain inside the building. By doing so, this will also lower the temperature differential between the interior air and the ceiling/walls. Later, when the exterior metal, ceiling, and walls begin to cool, the adjacent interior air will also be cooler, and condensation will be less likely to occur.
Reflective insulation also provides another line of defense against interior condensation. The bubble-core structure provides a thermal break separating the cooler air above the insulation, from the warmer air directly below. As a result, condensation will be much less likely to form on the interiorfacing surface of the reflective insulation.
Adequate ventilation
The next step in reducing interior condensation is ensuring adequate ventilation. This is important because higher interior humidity levels are directly related to condensation risk. Even in well-insulated buildings, other sources may exist that contribute to interior heat gain and humidity. If so, removing this added heat and humidity must be addressed. In addition to ventilation, improving interior air circulation and movement will also help reduce temperature and humidity levels.
Conditions vary by building type, use and climate. Knowing the conditions that contribute to your specific building is essential to eliminating moisture risk and addressing the problems that could lead to interior condensation.
Kelly Myers is national sales manager of rFOIL Insulation Products, Covertech Fabricating Inc., Shawnee Mission, Kan. For more information, visit www.rfoil.com.
