Roxul ComfortBoard IS - Manual (Page 15)

INSULATING SHEATHING FOR RESIDENTIAL CONSTRUCTION APPLICATION GUIDE 13
Thermal Control
As society demands that residential buildings consume less energy and generate less pollution,
minimizing the flow of heat through the enclosure has become an increasingly important function for the
enclosure to perform. The control of heat flow is also important for the control of interior surface
temperatures, and hence ensuring human comfort and avoiding cold weather condensation. Controlling
the temperature of various elements and layers within an enclosure assembly can be used to avoid
condensation or enhance drying, both of which influence durability.
R-value is commonly used to measure the thermal control of insulation products. However, this metric
does not account for the impacts of thermal bridging, air leakage, installation quality, or thermal mass. It
is this multitude of factors that working together delivers good thermal control.
Thermal bridging
Heat flow is often greater at corners, window frames, intersections between different assemblies, etc.
When heat flows at a much higher rate through one part of an assembly than another, the term thermal
bridge is used to reflect the fact that the heat has bypassed the thermal insulation.
Thermal bridges become important when:
 they cause cold spots within an assembly that might cause performance (e.g., surface
condensation), durability or comfort problems
 they are either large enough or intense enough (highly conductive) that they affect the total
heat loss through the enclosure
Thermal bridging can severely compromise thermal control and comfort in some building types. Heat
flow through steel stud walls is dominated by heat flow through the metal components (see Figure 5).
Figure 5: Best case R-values for walls with no extra framing for windows, floors or partitions.
Failure to break these thermal bridges can reduce the R-value of the insulating components by 50 to 80%.