As we look to meet new effective RSI values required in upcoming energy code provisions, and exceed these standards in high performance sustainable construction, the use of continuous insulation (uninterrupted by wall studs, plates, lintels, floor lines etc.) as part of our exterior wall assemblies is the way of the future. That being said, casually adding insulation to a wall assembly can also be extremely problematic if done incorrectly. When insulation values go up, the exterior sheathing plane becomes colder, leaving opportunities for condensation that must have the ability to dry to the exterior. Adding continuous insulation such as XPS (blue foam board insulation), which is extremely vapour impermeable restricts the ability for the wall assembly to dry as it creates the ‘double vapour barrier’ bag that can trap moisture within the wall assembly and lead to deterioration.
ROXUL Comfortboard IS is a rigid mineral wool insulation sheathing board that is non-combustible, water repellent, fire resistant and sound absorbent. Comfortboard IS is an exterior non-structural insulation sheathing that provides a continuous layer of insulation around the residential building envelope. Mineral wool insulation (such as Comfortboard IS) is hydrophobic (it can get wet), and highly vapour permeable such that it won’t limit exterior drying of the wall assembly. With the added rigidity of Comfortboard IS, rainscreen strapping and exterior cladding products can be installed directly over the insulation boards (fasteners penetrating through the panels into the structural framing).
For some context, a 2×6 wall (16″ centres) with standard R-20 batt insulation is rated at an effective R-Value of just under R-17. In some BC Climate zones (and the City of Vancouver) an effective R-value of R-22 is going to be the baseline standard. Adding a 1.25″ Comfortboard IS panel outboard of the sheathing plane bumps this wall assembly over the effective R-22 required (when considering the effective R-value of all components).
In high performance assemblies, we will likely see more instances of framing reduced to 2×4 construction to allow an increase in the exterior continuous insulation thickness without increasing the overall assembly thickness.