Which component of a roof can effectively prevent water leaks while still allowing air to leak?

The roofing membrane's termination is designed to create a seal at the edges and boundaries of the roofing system, which is essential for preventing water penetration. This sealing capability is critical because it acts as a barrier to water intrusion, especially at vulnerable points where the roof meets walls, parapets, or other structures. While it effectively prevents water leaks, it does not fully inhibit air leakage, especially in scenarios where there may be penetrations or gaps around the membrane's edges. This allows air to pass through while still maintaining the crucial role of water protection.

In contrast, the roof insulation primarily contributes to thermal performance and can help reduce energy loss but is not specifically designed to act as a water barrier. The roof drainage system is essential for directing water away from the roof surface, but it does not address air leakage directly. Similarly, the gutter system is crucial for channeling water away from the building's foundation but does not impact air sealing at the roof level. Thus, the roofing membrane's termination serves a dual function of water protection and partial allowance for air exchange, aligning perfectly with the question's requirements.