Green Roof Layer Stack: Evapotranspiration Cooling and Cistern Cascade

What Green Roof Layers Do

A green roof is composed of multiple layers designed to provide insulation, manage stormwater, and support vegetation. Each layer serves a specific purpose: the waterproofing membrane prevents water from reaching structural components; the drainage layer allows excess water to flow out while retaining enough for plant use; the growing medium supports plants and acts as a thermal buffer; and the vegetation itself performs photosynthesis and transpiration, which helps cool the roof surface.

The substrate layer holds the soil and provides stability for the plants. Beneath it lies the root barrier membrane that protects the waterproofing from roots, ensuring long-term integrity.

Evapotranspiration Cooling Mechanism

Evapotranspiration is a key process in green roof cooling. Plants absorb water through their roots and release it into the air as vapor via transpiration. This process not only cools the plant itself but also the surrounding air, reducing surface temperatures on the roof. The evaporation of water from the substrate and plants requires energy (latent heat), which is taken from the surrounding environment, thus cooling the area.

The efficiency of this cooling mechanism depends on factors such as temperature, humidity, wind speed, and solar radiation.

Cistern Cascade Function

A cistern cascade in a green roof system collects rainwater from the roof surface. This water is stored temporarily before being used to irrigate the plants. By reusing this water, the system reduces storm runoff and the load on municipal water supplies. Additionally, storing water helps maintain consistent soil moisture levels, which can improve plant health and enhance cooling efficiency.

The cistern cascade also contributes to reducing peak flow rates during storms, helping mitigate urban flooding and improving overall water management.

Comparison with Bare Roofs

When compared to bare roofs, green roofs offer significant benefits in terms of energy efficiency and environmental impact. They can reduce the heat island effect by lowering surface temperatures, which in turn reduces cooling demands for buildings below. This leads to lower air conditioning costs and a more comfortable indoor environment.

Moreover, green roofs contribute to better stormwater management, reducing runoff volumes and improving water quality through natural filtration processes.

Frequently asked questions

Try it live

Everything above runs in your browser — open Green Roof Layer Stack: Evapotranspiration Cooling and Cistern Cascade and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.