A green roof layers vegetation over a purpose-built waterproofing assembly: root barrier, drainage and retention layers, engineered growing media, and plantings. Extensive systems use shallow, lightweight sedum blankets that need little maintenance; intensive systems support deeper plantings and can create genuinely usable outdoor space.
The buried membrane is the quiet winner: shielded from UV and thermal cycling — the two forces that age every exposed roof — vegetative assemblies routinely deliver far longer membrane life. Add stormwater retention that eases the load on municipal systems, and the roof starts earning its keep.