What is a recommended method for insulating basement foundation walls?

The recommended method for insulating basement foundation walls is to install vapor impermeable insulation. This approach is effective because foundation walls are typically in contact with the ground, which can hold moisture. Vapor impermeable insulation helps to prevent moisture from the ground from penetrating into the basement space, thereby reducing the risk of mold growth and structural damage that can occur due to high humidity levels.

When moisture enters the insulation system, it can lead to thermal bridging, reducing the overall effectiveness of the insulation and potentially compromising the indoor air quality. By using vapor impermeable insulation, the insulation barrier acts as a shield, keeping the conditioned space dry and helping to maintain more consistent temperatures in the basement.

In contrast, while fiberglass batt insulation may have its uses in other parts of the home, it is less suitable for areas prone to moisture because it can absorb water, which diminishes its insulating properties over time. Similarly, air gap insulation materials and reflective insulation are not as effective for foundation walls where moisture is a significant concern. The need for a vapor barrier to eliminate moisture intrusion underscores why vapor impermeable insulation is the preferred choice in this application.