There are many ways of preventing condensation, a major concern of owners of steel buildings. Maintaining a reasonably low inside relative humidity is of prime importance. To achieve this, steel buildings are equipped with proper insulation, all leaks and holes are sealed, and a reflective barrier is used. In addition, outside air is allowed to mix with the warm moist inside air.
An insulation system with vapor barrier can close the building envelope to reduce heating and cooling costs, as well as prevent condensation. However, condensation can still occur in existing steel buildings because there is no insulation, not enough insulation, or the existing insulation is already torn, creating leaks.
Sealing air leaks and adding insulation to existing steel buildings is referred to as an insulation retrofit. Retrofitting insulation between roof purlins and wall girts involves filling the entire 8 inches cavity with insulation to avoid creating an air space where condensation can quickly form on the inside of the cold surface of the exterior panel.
For most cases where insulation was installed during construction of steel buildings, there may be a substantial heat loss at the area where the insulation blankets were compressed between the roof purlins and wall girts. The existing insulation provides a thermal break and adding faced fiberglass to fill the entire cavity of the purlins and girts will help prevent any further condensation to form against the exterior panels or the exposed steel members.
On the other hand, for existing steel buildings that have no insulation previously installed between the outside panels and the structural members, condensation issues are more difficult to deal with. It is not enough that the cavities between the purlins and girts are filled with faced fiberglass because condensation or frost can still form at the bottom of the structural members, when heat is introduced into the building. To remedy the situation, a thermal break tape or strips of rigid board insulation should be installed at the bottom of the purlin or girt.