Moisture Problems Associated with Building Insulation
The addition of thermal insulation into wall cavities has had a major impact on moisture control in buildings. As buildings have become tighter and better insulated, the opportunity for water vapor to dry out from wall and roof
assemblies has been reduced. Trapped water leads to wall assembly failures.
Buildings in cold winter climates will tend to dry to the outside since moisture flows from the warm interior towards the cold exterior. Under these conditions, water vapor passing through insulated building assemblies will reach a temperature where it will begin to condense. If this condensation occurs before the vapor reaches the exterior of the building, the insulation will become wet. Most insulation acts like a sponge, collecting moisture that is unable to escape. If an adverse moisture condition persists, mold and rot will affect the structure even when inorganic fiberglass insulation has been used.
In hot, humid conditions the situation is
reversed but equally problematic. When hot, moist air is allowed to enter the wall from the outside, it may condense in the insulation as it approaches the colder, air-conditioned space.
The insulation alone does not create the problem, but because of its absorbent nature it will often augment the problem. The type of vapor retardant barrier and its position in relation to the insulation are critical in preventing mold and rot from developing. The general principle is to install the vapor retardant barrier so that it prevents the travel of moisture into the insulated cavity without impeding the ability of the moisture to escape. The dilemma is that climatic conditions may vary widely on a daily and seasonal basis, creating mixed conditions. This makes insulation and moisture
