A Warmer Wall Reduces Condensation Potential and Maximizes Thermal Performance.Temperature: Key to Condensation Control
Adjusting the permeability of the layers in a wall assembly can help manage moisture. But such design strategies require exacting installation and consistent long-term permeability of the influential layers.
Since condensation is caused by temperature changes, the ultimate method for controlling condensation is to control the temperature within the wall assembly with the proper application of thermal insulation. Thermal insulation not only reduces heat flow, it also changes the temperature gradient in the wall. Proper placement of the right amount of insulation can dramatically reduce the potential for condensation in a steel stud wall.
Temperature Within a Typical Steel Stud Wall
A typical steel stud wall consists of steel studs with batt insulation in the stud cavity. The outside surface of the steel stud assembly is typically faced with exterior gypsum with a brick exterior fascia.
As shown in Figure 1, the interior surface of the exterior gypsum is 12ºF. At this low temperature, the potential for condensation of any water vapor that reaches this surface is very high. Sealing the cavity with low permeance materials like polyethylene film is a possible solution, but demands excellent installation and the wall will forever be dependent on the film's quality. In addition, the thermal performance of this solution is not very good: an effective R-value of about R-9.31, far less than the R-13 anticipated from the installation of batt insulation in the cavity.
The THERMAX™ Wall System solution replaces the exterior gypsum with 1.55" thick THERMAX™ (ci) Exterior Insulation and the batt insulation with 1.5" thick STYROFOAM™ Brand SPF (CM Series). The inside surface temperature has warmed up to 61ºF. The effective R-value of this wall is R-16.8. (Figure 2.)
The wall's performance can be improved even more by using 2" thick THERMAX™ (ci) Exterior Insulation. Here, the temperature of the insulation's interior surface has increased to 63ºF. The cavity is now a conditioned space - and the chance for condensation is near zero. This slight increase in the insulation thickness results in a total effective R-value of R-19.7. (Figure 3.)