Installing 2-inch rigid extruded polystyrene (XPS) foam

A look at the features, benefits and installation techniques of attaching rigid continuous exterior insulation boards.

There are many innovative ways to increase the energy efficiency in new wall construction, but considering that 130 million of the residential structures in the United States are already built, with a median construction age of 40 years old, according to the 2013 U.S. Census, we need effective solutions to increase the thermal performance of the existing building stock.∫

Attaching rigid continuous exterior insulation boards − Extruded Polystyrene Insulation (XPS) foam − to the exterior walls is one such method and is an effective alternative to drilling and filling cavities.

Exterior insulation creates an uninterrupted layer, which is a good way to address thermal bridging through wood studs and rim joists. It provides exceptional moisture resistance and can be applied over existing cladding, sheathing materials or directly to the studs.

Another advantage is that by putting the insulation on the outside rather than in the cavity, the dew point (when vapor condenses into water) is moved towards the exterior of the wall potentially reducing the wall getting wet in the first place. We recommend application of a weather resistive barrier under the exterior insulation, but it can also be applied over the exterior insulation.