There are usually specific reasons why architects, builders, contractors and building owners prescribe insulation choices for wall insulation products and systems in both residential and commercial structures. Sometimes though, old habits continue because they’re comfortable, and they work. Batt insulation, sometimes referred to as cavity insulation or blanket insulation, may be a good choice for some projects. It’s been used traditionally because of it’s low cost and simple installation inside the wall cavity. Understanding the performance characteristics of continuous insulation, however, make it much more than an exceptional product recommendation. It’s a logical choice for many climate zones, wall assembly types and wall applications.
With recent energy performance characteristics of a new or retrofit structure taking on increasing importance, thermal bridging is a more familiar topic of discussion. Thermal bridging is a heat transfer dynamic that occurs when penetration of the insulation takes place through the interior or exterior of a structure via a highly conductive non-insulating material. For example frost or cold traveling through steel studs from from an exterior material such as OSB to an interior materials such as gypsum board.
Among the recent arguments against the performance of cavity insulation is, insulation near the thermal bridge is of little value since the heat loss or transfer can still occur through the bridge materials. Even though batt insulation does provide some protection by insulating a broad swath of space, the lack of continuity prohibits the highest possible levels of performance.
There are statistics which suggest that in a wood frame home nearly 20% of any energy loss in the homes structure is the result of thermal bridging, including door and window openings. In a steel frame building with batt insulation between the studs, it’s estimated that this energy loss number could be as high as 50%.
Continuous insulation blocks thermal bridging on cavity walls and prevents it from happening in areas where there are no adjacent openings. Where door and window openings are flashed, continuous insulation reduces heat transfer in these areas as well.
When continuous insulation is used on the exterior surface of the studs, the temperature differential between the cavity and the studs is minimized, preventing the transfer of heat or cold. Continuous insulation can be specified as a replacement for non-insulating sheathing such as OSB, in order to prevent heat and cold from moving through the studs.
Additionally the wall cavity temperature is warmer and more consistent when continuous insulation is used, reducing the risk of condensation within the wall cavity. When a drainage plane and moisture barrier are combined in a continuous insulation wall assembly, there is better protection against moisture intrusion. This serves to prolong the life of the structure by slowing material degradation due to damage from the elements.The shell of the structure is tighter, reducing airflow and adding to structural integrity.
The wall profile itself is sometimes thinner while greater R-value is achieved. Polyiso has the highest R-value per square inch of any insulation material, so not as much material is required to achieve a superior R-value.
New projects that require measurable thermal performance and look to achieve air tightness and energy efficiency, or recognition such as LEED credits should seriously consider continuous insulation as the insulation method of choice.