A waterproofing membrane is a crucial component of a green roof system. It's a continuous, impervious layer that prevents water from penetrating the roof deck and entering the building. The membrane acts as the primary defense against leaks and water damage. In a green roof system, the waterproofing membrane is installed directly on the roof deck, beneath the drainage layer and the growing medium. It's essential to choose a high-quality, durable waterproofing membrane specifically designed for green roof applications to ensure long-lasting protection.