Below you will find an overview of frequently asked questions. If you have a question, you cannot find the answer to, please do not hesitate to contact us. We are happy to assist you.

Roof pitch and roof load.

How much does a Detention Roof weigh?

A Detention Roof weighs approximately 90 kilograms per m² when saturated. When completely unsaturated, the Detention Roof weighs only about 25 kilograms per m².

Can a Detention Roof be applied on a sloping roof?

A Detention Roof can be applied on a roof with a maximum pitch of 5 °.

Why is the Detention Roof a lightweight solution?

The Detention Roof is a lightweight solution, as the Storage Layer HC40 and Detention Layer T5 are only occasionally filled with water. The constant weight mainly consists of the Sempergreen Sedum-mix blanket and the Urbanscape Green Roll. These are components that retain water for a longer period of time and therefore retain a heavier weight for a long time. This weight is comparable to Sempergreen's lightweight green roof solutions.


What does the maintenance of a Detention Roof consist of?

A Detention Roof is low maintenance. Still, your Detention Roof will always need a little maintenance. This includes removing blown-in weeds and fertilizing several times a year. Preferably, carry out maintenance in the spring and autumn. In addition, check whether the drainage system is still functioning. Remove any blown-in leaves. To carry out this maintenance, it is no problem to walk on the Sedum plants. Sedum is strong enough to handle this.


How much water can the Detention Roof store?

The Detention Roof can store a total of 69 to 74 liters per m² of water. Specified by layer, the Sempergreen Sedum-mix blanket and Urbanscape Greenroll together can absorb 34 to 39 liters per m². The Storage Layer HC40 and Detention Layer T5 do not absorb water, but only temporarily detain rainwater. The Storage Layer HC40 is a temporary water column in case of heavy rain showers, while the Detention Layer T5 creates friction, so that the rainwater is pushed upwards to the water column above. Together these two layers can temporarily store 35 liters per m². This brings the total water storage capacity of the four layers to 69 to 74 liters.

How does the Detention Roof work in comparison to a traditional green roof with regard to relieving the sewerage system?

Both a traditional green roof and a Detention roof contribute to the relief of the sewerage system. A traditional green roof collects 85% -90% of the rainwater per year. However, during multi-day storms or peak showers, a traditional green roof is in general insufficiently able to provide added value in relieving the sewer system. A Detention Roof proves its added value especially during peak showers and multi-day storms by collecting and delaying runoff of excess rainwater. This prevents damage and flooding from excess rainwater at precisely these critical moments.

Can the water in the Detention Roof freeze during extremely cold periods?

The chance of freezing is very small. Within 2 to 3 days, the rainwater, which is in the Storage Layer HC40, will be drained. The Sempergreen Sedum-mix mat on top has an insulating effect, so it takes a while for frost to reach the underlying layers. So before the cold has a chance to freeze that water, the rainwater has already drained.

Subsidy and sustainability.

Can I receive a subsidy on my Detention Roof?

More and more municipalities and water boards are providing subsidies to stimulate the use of green (blue) roofs. Green (blue) roofs are an important tool in the fight against climate change and to maintain a pleasant living environment in the municipality. Please inform at your municipality or water board about the possibilities.

Does a Detention Roof contribute to BREEAM or LEAD points?

BREEAM and LEED are the most widely used sustainability certifications for new and existing buildings. A Detention Roof contributes to the score for BREEAM or LEED for both new and existing buildings, always in combination with a set of other measures. Since the certification process involves many factors, a uniform score cannot be stated. The result will differ per project. Nonetheless, the application of a Detention Roof will lead to a directly measurable reduction of water and energy consumption and more efficient use of the building. This will also result in cost savings.

Water calculation for your project

Would you like to know how a Detention Roof can contribute to your project? Request a water calculation.

Request here