What about water drainage from a green roof?
Green roof Oud-Beijerland
One of the more important benefits of installing a green roof is the ability of a green roof to store water to make stormwater runoff more gradual.
In this article, we will discuss with you how the ”traditional” roof drains water and how a green roof does so, along with all its benefits.
Let’s start by describing the drainage of a traditional roof.
Traditional drainage
A traditional drain, and we’re talking about a flat roof, causes water to enter the sewer through a gutter and then a downspout.
Usually the water enters the drainpipe through a gravel tray. The gravel tray ensures, by means of a grate, that leaves and gravel are stopped so that the drainpipe does not clog.
Whether it is a zinc downspout, a plastic downspout or a steel downspout, the water disappears into the sewer just as quickly and does not return.
When the traditional system is used to drain water from roofs, it can result in both the roof itself and the sewer system not being able to handle the drainage of the water.
The result of the above situation is that either the roof remains full of water, or the sewer overflows when there are heavy downpours.
Things are a little different with a green roof!
Drain green roof
Basically, with a green roof, water runs down it the same way, only with the green roof as an intermediate station.
The green roof absorbs significant amounts of rainwater. The sedum (and/or other plants) return the moisture to the atmosphere via evaporation.
Of course, the plants cannot absorb all the moisture from the green roof. Some of the water is absorbed into the substrate layer; this eventually evaporates again.
If we take stock after this, about ten to fifty percent of the rainwater still ends up in the sewer after the water encounters the green roof.
You might think that there is a forty percent margin in between in terms of rainwater what ends up in the gutter. It depends on what substrate is used, what drainage is used and what kind of vegetation is on the roof.
