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How to thoughtfully manage water harvesting on a blue roof?

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How to thoughtfully manage water harvesting on a blue roof?
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A blue roof surpasses a green roof in buffering capacity, acting as a harvesting system on the roof. As a designer, you can achieve multiple goals at once: saving valuable ground-level space and avoiding additional costs for constructing buffer basins or tanks. An additional benefit is the reduction of pressure on the sewer system during heavy rainfall.

"A technically correct retention roof requires attention right from the design phase," says Philip Bruon, Product Manager at Tectum Group. "Ensuring the stability of the building to support the additional load is crucial, and for optimal water buffering by a retention system, the roof should not have a slope."

Choosing the right insulation

The additional water load also imposes higher requirements on the roof insulation.

"This must have a sufficiently high pressure resistance. According to Buildwise and the guidelines of the UBAtc, the possibilities are very limited. Only cellular glass, XPS and in some cases EPS can be used in combination with a blue roof. The commonly used PIR insulation is therefore not a suitable choice for a retention roof," says project manager Sven Devlieghere.


To learn more about the appropriate insulation in combination with green roofs, read our article 'PIR insulation is not suitable for intensive green roofs'

Static or dynamic blue roof

The roof edges should be designed high enough to accommodate the thicker roof structure. The more water you want to buffer on the roof, the higher the structure will need to be.

"Then there is the choice of a static or dynamic blue roof. A static blue roof has a delayed discharge of rainwater, facilitated by a pinched drain. In contrast, a dynamic blue roof incorporates a control system that releases water based on weather forecasts. This enables the maximization of storage capacity, buffering rainwater for dry periods. In anticipation of heavy rain, the system releases some of the stored water, alleviating pressure on the roof. This way, there is no additional pressure on the sewer system during the rainy season. If the retention roof is adorned with a green roof, the rainwater can also be utilized for plants through capillary action. In the case of an authentic blue roof, it may also be considered to make the water visible. This adds aesthetic value and serves as a watering spot for birds and insects. In some German states, the government is convinced of the added value of blue roofs. They offer an incentive in the form of a tax rebate on water discharge if the owner provides a water buffer on the roof," says Philip Bruon.

Perfectly usable water

There is a common perception that water buffered on green roofs cannot be reused for flushing toilets. "This is a misconception," says Philip Bruon. "With a good pre-filter, the water is perfectly usable. In the first 3 to 4 years, there may be a brown discoloration due to the organic material present in the substrate. However, this is not a problem in itself. It is a matter of perception and information. In fact, this discoloration can be avoided by using an activated carbon filter.

Quote icon in green

With a good pre-filter, water buffered on green roofs is perfectly usable for toilet flushing.

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News
>
How to thoughtfully manage water harvesting on a blue roof?

A blue roof surpasses a green roof in buffering capacity, acting as a harvesting system on the roof. As a designer, you can achieve multiple goals at once: saving valuable ground-level space and avoiding additional costs for constructing buffer basins or tanks. An additional benefit is the reduction of pressure on the sewer system during heavy rainfall.

"A technically correct retention roof requires attention right from the design phase," says Philip Bruon, Product Manager at Tectum Group. "Ensuring the stability of the building to support the additional load is crucial, and for optimal water buffering by a retention system, the roof should not have a slope."

Choosing the right insulation

The additional water load also imposes higher requirements on the roof insulation.

"This must have a sufficiently high pressure resistance. According to Buildwise and the guidelines of the UBAtc, the possibilities are very limited. Only cellular glass, XPS and in some cases EPS can be used in combination with a blue roof. The commonly used PIR insulation is therefore not a suitable choice for a retention roof," says project manager Sven Devlieghere.


To learn more about the appropriate insulation in combination with green roofs, read our article 'PIR insulation is not suitable for intensive green roofs'

Static or dynamic blue roof

The roof edges should be designed high enough to accommodate the thicker roof structure. The more water you want to buffer on the roof, the higher the structure will need to be.

"Then there is the choice of a static or dynamic blue roof. A static blue roof has a delayed discharge of rainwater, facilitated by a pinched drain. In contrast, a dynamic blue roof incorporates a control system that releases water based on weather forecasts. This enables the maximization of storage capacity, buffering rainwater for dry periods. In anticipation of heavy rain, the system releases some of the stored water, alleviating pressure on the roof. This way, there is no additional pressure on the sewer system during the rainy season. If the retention roof is adorned with a green roof, the rainwater can also be utilized for plants through capillary action. In the case of an authentic blue roof, it may also be considered to make the water visible. This adds aesthetic value and serves as a watering spot for birds and insects. In some German states, the government is convinced of the added value of blue roofs. They offer an incentive in the form of a tax rebate on water discharge if the owner provides a water buffer on the roof," says Philip Bruon.

Perfectly usable water

There is a common perception that water buffered on green roofs cannot be reused for flushing toilets. "This is a misconception," says Philip Bruon. "With a good pre-filter, the water is perfectly usable. In the first 3 to 4 years, there may be a brown discoloration due to the organic material present in the substrate. However, this is not a problem in itself. It is a matter of perception and information. In fact, this discoloration can be avoided by using an activated carbon filter.

News
>
How to thoughtfully manage water harvesting on a blue roof?

A blue roof surpasses a green roof in buffering capacity, acting as a harvesting system on the roof. As a designer, you can achieve multiple goals at once: saving valuable ground-level space and avoiding additional costs for constructing buffer basins or tanks. An additional benefit is the reduction of pressure on the sewer system during heavy rainfall.

"A technically correct retention roof requires attention right from the design phase," says Philip Bruon, Product Manager at Tectum Group. "Ensuring the stability of the building to support the additional load is crucial, and for optimal water buffering by a retention system, the roof should not have a slope."

Choosing the right insulation

The additional water load also imposes higher requirements on the roof insulation.

"This must have a sufficiently high pressure resistance. According to Buildwise and the guidelines of the UBAtc, the possibilities are very limited. Only cellular glass, XPS and in some cases EPS can be used in combination with a blue roof. The commonly used PIR insulation is therefore not a suitable choice for a retention roof," says project manager Sven Devlieghere.


To learn more about the appropriate insulation in combination with green roofs, read our article 'PIR insulation is not suitable for intensive green roofs'

Quote icon in green

With a good pre-filter, water buffered on green roofs is perfectly usable for toilet flushing.

April 30, 2024

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