Continuous thermal insulation is the backbone of a zero energy building's envelope. High insulation values in the roof, the walls, and below grade are typically needed: this allows the design team to reduce the capacity of the HVAC system and save on first costs as well as long-term operating costs.
Ideal insulation types and values will differ by climate, but for most buildings, continuous exterior insulation is the recommended method to reduce thermal bridging. In cavity walls, open-cell sprayed polyurethane foam or dense-packed cellulose are recommended in addition. Batt insulation is not recommended in wall cavities.
Continuous exterior insulation is also ideal for below-grade walls. Rigid extruded polystyrene board is suitable for this application. While interior insulation of below-grade walls has been common in the past, continuous exterior insulation limits moisture management issues, makes air-barrier and insulation continuity easier, and better accommodates the use of thermal mass for energy efficiency.
Photo: Achim Hering, CC BY 3.0