reliable waterproofing membrane: Leaks in green roofs can be very difficult to identify, and repairs or replacement can be expensive. For a long, maintenance-free life, green roof waterproofing must be sufficiently elastic to withstand building movement, must withstand ponded water, must be non-biodegradable, and must be resistant to root penetration. Some rubber and plastic sheet-applied and liquid-applied membranes meet these criteria but most asphalt products do not.