Green Roof Water Retention

Retention works like this.

Green roof water retention.

Suitable for blue roofs. 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. 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.

We need to think differently about the main purpose of a green roof. Discharge coefficient cs according to fll. 0 01 0 17 at 2 roof pitch. Note that there was very little if any runoff during the may 1 to sept 30 growing season.

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. However a purple roof retains more water than any other green roof concept. The secret of green roof water retention is green. High level of reduction of of water discharge during high intensity rainfall whilst retaining good drainage even for large roof areas peak discharge.

The purple roof is the only concept that has been exposed to real life assembled testing in a professional setting. Yes every green roof absorbs and buffers water. Green roofs are also known as vegetative or eco roofs. Geofabrics manufacture water retention and drainage boards designed specifically for living roofs.

Water storage and discharge delay. 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. 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. Drainage and water retention elements with low medium or high retention capacity are components of the green roof system.

The cuspate is overlaid by a bonded geotextile to prevent any blockages. This means that the water leaves the roof as vapor. Fcp20 is a composite which is made of a cuspated sheet material with water retention cups to store water to promote healthy growth. System solutions with defined water retention.

Green roof solutions offers many different drainage layer options depending on system goals regarding water retention. 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.