Root barriers on Green Roofs protect the water proofing against penetration of plant roots.
You also have to think about root protection when considering a Green Roof.
As plant roots develop, they look for water. During a period where water is scarce, plant roots will travel to the last place water will be present on a roof, and that could be along seems and details within the roofing membrane. Some plants have invasive root systems that can penetrate a roofing membrane, resulting in roof leaks.
To protect the roofing membrane, we recommend installing a material with a high puncture resistance and avoid plants that develop a strong root system.
There are also roofing membranes on the market that can function as both a roofing membrane and as a root barrier. EPDM and TPO roofing membranes have been used in the past as a single- ply waterproofing that are resistant to root penetration.