What is a critical requirement when insulating rafters for ventilation?

Leaving a minimum air space of 1 inch when insulating rafters for ventilation is vital to ensure proper airflow and reduce the risk of moisture accumulation. This airspace allows air to flow freely through the rafter system, facilitating the ventilation of any trapped moisture and helping to maintain a healthy roof structure. Adequate ventilation is crucial for preventing issues such as mold growth, wood rot, and energy inefficiencies.

Rafters need to be insulated while still allowing for ventilation pathways, which is why a 1-inch minimum airspace is recommended. This spacing provides enough room for air circulation while also allowing for adequate insulation coverage. Failure to observe this requirement can lead to heat buildup in the attic space and other negative consequences related to improper ventilation.

While a 2-inch air space may enhance airflow, it is the minimum requirement of 1 inch that is essential for maintaining a balance between insulation effectiveness and ventilation needs. Covering the rafters completely or using only rigid insulation materials could lead to insufficient air movement and ultimately compromise the roof's integrity over time.