Green Roof Water Retention

Later the sun comes out and the plants use the rainwater to evapotranspire.

Green roof water retention.

The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall. Rain falls onto a relatively dry green roof and the green roof absorbs the water usually in pore spaces. Green roofs typically provide stormwater retention as they capture water preventing water from draining and then allow the water to evaporate only through evapotranspiraton processes. Green roof growing medium is composed of mineral aggregates and only a small amount of organic material.

The water needs to be drained off to create sufficient storage capacity in time for the next rainfall. Evapotranspiration et plays a major role in the retention performance of green roofs due to removal of stored water and the corresponding increase in volume available for storage in the green roof medium for subsequent precipitation events. Yes every green roof absorbs and buffers water. This means that the water leaves the roof as vapor.

The purple roof is the only concept that has been exposed to real life assembled testing in a professional setting. It should have good consistent drainage and aeration with a structure that enables it to hold water. Such an extensive green roof will have a water retention capacity up to 44 l m and a surface weight in water saturated condition about 130 kg m. However a purple roof retains more water than any other green roof concept.

This type of water roof is called a water roof for rainwater retention. The secret of green roof water retention is green retention works like this. When the depth of water stored in the green roof growing media was treated as a variable roof storage was varied from 0 25 to 3 0 inches of storage using the 28 years of state college s daily rainfall data the results see figure 3 showed that the 3 5 inch green roof with 1 6 inches of water storage with a drainage layer and plants was an excellent choice. The water only remains on the roof for a short period of time after rainfall.

Traditional soil is heavy and packs tight after repeated rains reducing water retention and aeration for plant roots. Drainage green roof solutions offers many different drainage layer options depending on system goals regarding water retention. The rainwater is drained off at a delayed pace using a narrower lower situated opening. Water retention is really important in case of pitched roofs because their drying trend is more pronounced.