Exterior Insulation: How Continuous Rigid Foam Changes Your Home's Performance

Exterior Renovation Services

Installing continuous rigid foam insulation under new siding is the most effective exterior thermal upgrade available — it eliminates thermal bridging that cavity insulation can't address.

Thermal bridging is the transfer of heat through solid structural elements that penetrate the wall assembly. In a standard stick-framed wall, every wood stud is a pathway for heat transfer that bypasses the batt insulation between studs. Continuous rigid foam installed on the outside of the sheathing wraps the entire wall — including the studs — in insulation, eliminating this bypass path.

Planning Your Project

The performance difference is quantifiable. A wall framed at 16-inch on-centre has approximately 25% of its surface area occupied by studs. If the stud R-value is R-5 and the cavity insulation is R-20, the effective wall R-value is significantly less than R-20. Adding 1.5-inch rigid foam (R-7.5 to R-10) over the exterior more than compensates for this bridging effect.

Rigid foam type matters. EPS (expanded polystyrene) is the most commonly used and most cost-effective option. XPS (extruded polystyrene) is denser and moisture-resistant, suitable for below-grade or high-moisture applications. Polyiso has the highest R-value per inch but performs less consistently at low temperatures, making it less suitable for cold Ontario climates.

Working With D&D Exterior Finishing

Moisture management is the critical design consideration when adding exterior insulation. The foam layer moves the dew point within the wall assembly. If the foam layer isn't thick enough, condensation can occur within the wall cavity, causing moisture damage. D&D Exterior Finishing designs exterior insulation assemblies to Ontario climate zone standards to ensure correct moisture behaviour.