Which type of insulation is commonly installed below the roof sheathing for air-impermeable insulation?

Closed-cell spray foam insulation is commonly installed below the roof sheathing for air-impermeable insulation due to its unique properties. This type of insulation forms a rigid, solid barrier that is highly effective at resisting air movement. When applied, closed-cell spray foam expands and encapsulates the space, creating a continuous layer that minimizes air infiltration and enhances energy efficiency.

In addition to its air-impermeable qualities, closed-cell spray foam has a higher R-value per inch compared to other insulation types. This means it provides superior thermal resistance, contributing to improved climate control within the building structure. Its moisture-resistant characteristics also make it a suitable option for areas where humidity might be a concern, as it helps prevent condensation issues that could lead to mold growth or structural damage.

In contrast, other types of insulation, such as fiberglass batts and open-cell spray foam, do not offer the same level of air sealing. Fiberglass batt insulation can allow air to pass through if not meticulously installed, leading to thermal bridging and potential energy loss. Open-cell spray foam, while providing some air sealing, is less dense and more permeable than closed-cell foam, which means it does not provide the same level of moisture resistance and structural integrity.

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