A green roof is a roofing system that supports vegetation, using layers to manage water, roots, and thermal insulation. The underlayment beneath this system plays a crucial role in protecting the roof deck from moisture and root intrusion, which could cause leaks or damage if left unchecked. Typically, the best underlayment for a green roof is a high-quality waterproof membrane, often made from materials like EPDM (ethylene propylene diene monomer) or TPO (thermoplastic olefin). These membranes are designed to withstand prolonged water exposure and provide a solid barrier against root growth. It's common for green roofs to include a root barrier layer as part of the underlayment system to prevent roots from penetrating the membrane and compromising the structure beneath the plants.
Diagnosing underlayment issues can be tricky because problems often show as leaks or mold inside the building, rather than obvious roof surface damage. Safe DIY checks include looking for signs of water stains on ceilings or walls beneath the roof and ensuring gutters and drainage are clear to prevent water pooling on the green roof surface. If signs of leaking or plant overgrowth below the expected level appear, it’s time to call a roofer experienced with green roofs. When consulting a contractor, ask whether their proposed underlayment includes a root barrier and what warranty they offer on the waterproof membrane, especially regarding root resistance and durability under constant moisture. This helps ensure the green roof will protect your home long-term without costly repairs down the line.