Do you often experience a large layer of water on your flat roof after a heavy rain shower? A green roof offers a natural and effective solution to reduce flooding and protect your roofing.
Why water on a flat roof is a problem
In the Netherlands, we're increasingly experiencing extreme rainfall. When too much water accumulates on a flat roof, it can lead to unpleasant situations. The weight of the water strains the structure, and stagnant water increases the risk of leaks and algae growth. You can read more about this in our article " Causes and Risks of Standing Water on a Flat Roof ."
A green roof, often consisting of sedum plants, acts as a natural sponge. Instead of all rainwater flowing directly to the downspout, a large portion is absorbed by the plants and the substrate. This process, also known as water retention, significantly reduces the burden on the sewer system during peak loads.
The benefits of sedum for water retention
Depending on the thickness of the layer, a green roof can retain 45% to 90% of rainwater. This water later evaporates through the plants, which also provides a cooling effect in summer. For those wondering how much water can remain on a flat roof , a green roof offers reassurance: it regulates drainage naturally.
Technical solutions for extreme rainfall
Although a green roof absorbs a lot of water, saturation can still occur during extreme downpours. In such cases, good drainage is crucial. It's important to keep the emergency overflows clear of substrate or leaves. For situations where the water level does rise too high, a submersible pump with a shallow suction offers a solution.
Flat suction submersible pump
With such a pump, you can quickly and efficiently remove excess water, almost to the roof surface. This is an ideal backup for green roof owners who want absolute security during storm season.
Maintenance and prevention
A green roof is relatively low-maintenance, but not maintenance-free. It's essential to check the drains at least twice a year. The following step-by-step plan: Cleaning your gutters and drains yourself offers useful tips for this. If you notice that, despite the green roof, excessive water remains, there may be a blockage or a structural defect. In that case, it's advisable to consult an expert, as described in "When should you call a roofer for water on your roof? "
Gardena Garden Hose 25m 19mm
To control the water you pump from your roof and drain it to a lower garden or well, a sturdy downpipe is essential. This prevents the water from flowing directly back into your home's foundation.
How much water exactly does a green roof hold back?
On average, a standard sedum roof retains between 20 and 35 liters of water per square meter. This significantly slows down the flow of water to the sewer, reducing the risk of street flooding.
Can a green roof be installed on any flat roof?
Not every roof is suitable. The structure must be able to support the weight of the plants, the substrate, and the absorbed water. A saturated green roof easily weighs 80 kg per m².
What should I do if puddles remain on my green roof?
If puddles are still visible on the green roof after 24 hours, the drainage is likely clogged. Check the leaf traps and drain points. In an emergency, you can use a vacuum to remove the water manually.
Share:
Roof Inspection Checklist for Fall: Prevent Water on a Flat Roof
Consequences of water accumulation for the roof covering