Retention Green Roofs

A retention green roof is a vegetated roof system designed to store rainwater in its layers (substrate, drainage) and release it slowly via evapotranspiration (plant release + evaporation) and controlled drainage, acting as a sponge to reduce stormwater runoff, prevent sewer overflow, and mitigate flooding, creating a "Sponge City" effect. It delays water release for hours or days, unlike simple green roofs, making it a key tool for sustainable urban water management.

Key Features:
  • Water Storage: Uses specialized layers (deep substrate, drainage mats) to hold significant amounts of water.
  • Delayed Release: Slows down water runoff, preventing overwhelming drainage systems during heavy rain.
  • Evapotranspiration: Plants release water vapor, returning it to the atmosphere, a process called retention.
  • Detention: Often combined with detention (temporary holding before release) for maximum stormwater control.
Benefits:
  • Reduces urban flooding.
  • Provides cooling and insulation.
  • Reuses captured water.
  • Improves urban microclimates and fights heat island effects.
How it Works:
Rain falls on the plants, gets absorbed by the substrate, and excess water fills the drainage layer below. This water is either taken up by plants (transpiration) or evaporates (evaporation), while a controlled outlet slowly releases the rest, mimicking natural water cycles.