Green Roof Water Retention

Rain falls onto a relatively dry green roof and the green roof absorbs the water usually in pore spaces later the sun comes out and the plants use the rainwater to evapotranspire.

Green roof water retention.

Green roofs are also known as vegetative or eco roofs. High level of reduction of of water discharge during high intensity rainfall whilst retaining good drainage even for large roof areas peak discharge. Retention works like this. Yes every green roof absorbs and buffers water.

We need to think differently about the main purpose of a green roof. The cuspate is overlaid by a bonded geotextile to prevent any blockages. 0 01 0 17 at 2 roof pitch. Our company offers consultancy and turnkey projects for green roof and terrace design landscape and long term maintenance in order to obtain the best results.

However retention is not always effective as it fills up the entire empty storage space in green roofs and then takes time to dry out and make room for new rainwater. Drainage and water retention elements with low medium or high retention capacity are components of the green roof system. The most critical role of the drainage layer is to provide an adequate flow of water off the roof during and after rainfall. 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.

Green roof solutions offers many different drainage layer options depending on system goals regarding water retention. Geofabrics manufacture water retention and drainage boards designed specifically for living roofs. However a purple roof retains more water than any other green roof concept. They fall into three main categories extensive intensive and semi intensive.

Although there are no precise definitions of them an extensive green roof has a shallow growing medium usually less than six inches with a modest roof load limited plant diversity minimal watering requirements and is often not accessible. Discharge coefficient cs according to fll. Fcp20 is a composite which is made of a cuspated sheet material with water retention cups to store water to promote healthy growth. Water storage and discharge delay.

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. This means that the water leaves the roof as vapor. Figure 2 shows the daily rain and associated daily green roof runoff for 1993 in state college pa for a green roof having a maximum of 1 6 inches of water retention storage. The secret of green roof water retention is green.

Note that there was very little if any runoff during the may 1 to sept 30 growing season. Suitable for blue roofs.