Can I Use Foam Board Insulation For Exterior Walls?

Choosing the Right Foam Board Insulation

When selecting foam board insulation for exterior walls, consider a thick, rigid product like polyisocyanurate (PIR) or expanded polystyrene (EPS) foam with a minimum R-value of 8. These materials are more resistant to moisture and external damage. Opt for a foam board with a thickness of at least 2 inches (50 mm) to achieve optimal R-values. Always check the manufacturer’s recommendations for specific R-values and installation guidelines.

Exterior Wall Insulation Installation

To ensure a tight seal and prevent moisture damage, install foam board insulation on the exterior of the wall, with a waterproof vapor barrier on the exterior side. This will prevent moisture from entering the wall cavity. Apply a thin layer of spray foam adhesive or a specialized foam board clip system to secure the foam board to the exterior sheathing. Use a 1/4-inch (6 mm) gap between foam board panels to allow for thermal expansion and contraction.

Additional Considerations

When using foam board insulation for exterior walls, consider the risk of thermal bridging, where conductive materials like studs or fasteners compromise the insulation’s effectiveness. To mitigate this, use insulation-rated fasteners and consider adding a thermal break, such as a layer of spray foam or mineral wool, to the studs. Additionally, ensure that the foam board insulation is properly secured to the exterior sheathing to prevent wind-driven rain from entering the wall cavity.