LISTEN...

When you add an air barrier and extra insulation to the exterior of a building, you'll be dealing with windows and doors that are now inset into the wall instead of flush to the surface.

The diagram above shows three scenarios, from top to bottom:

• Poorly performing window in a typical opening
• Ext. insulation applied without a thermal break, still not performing well.
• Best situation - exterior insulation added, thermal break, window is incorporated in the air tight layer and thermal layer.

The little thing that looks like a pitchfork or trident is Psi - a Greek symbol that represents the linear heat loss (conductance in U-Value) in thermal bridging. The more air tight and thermally upgraded you make an assembly, the more that thermal bridging becomes an issue.

Providing for a thermal break requires some planning and perhaps a replacement of a window. Remember the 'levels of intrusion' - how much surgery do you want to do...and how much can the owner afford?