What additional insulation should be installed below the roof sheathing in cold climates?

In cold climates, installing air-impermeable insulation below the roof sheathing is essential for several reasons. This type of insulation helps to reduce air leakage, minimizing heat loss from the living space to the outside. By ensuring that the insulation is air-impermeable, it creates a barrier that helps to maintain indoor temperatures, reducing the energy needed for heating and enhancing overall energy efficiency.

Moreover, in cold climates, the risk of condensation forming within the roof assembly increases. Air-impermeable insulation can help to limit the movement of warm, moist air from the interior into the colder areas of the roof assembly, thereby reducing potential moisture problems such as mold growth or roof sheathing deterioration.

While reflective insulation, foam board, and mineral fiber insulation have their benefits, they do not specifically provide the same level of air leakage control as air-impermeable insulation does in critical cold climate applications.