Designing climate resilient Blue Roof attenuation systems.

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Given the unprecedented extremes in climate change that the UK has experienced in the last few years, local and national planning policies have developed to ensure that developers, architects and engineers fully consider the impact that a changing climate will have on the performance of buildings.

For example, the recently revised London plan requires developers to incorporate ‘urban greening’ on new developments, and to consider rainwater water reuse as the priority in managing surface water runoff. This has seen a substantial increase in specification of blue roof attenuation systems, which are seen as an ideal method for managing both extremes of climate change in conjunction with green roofs, as they control run off and can help mitigate the effects of summer storms and the flash flooding, they can cause. Blue roofs also provide the added benefit of enabling water to be reused either as a passive irrigation system or as a more conventional rainwater harvesting system.

However, the design of blue roof attenuation systems is not governed by any specific standards, and it is important to understand the differences in function of a flat roof system and that of a blue roof attenuation system. The design of flat roof systems is governed by a well-established range of British and European standards, as well as Building Regulations. These standards promote the fast and efficient removal of rainwater from the roof surface, as the longer the rainwater sits on the roof the greater the risk of water ingress into the building.

A blue roof attenuation system on the other hand is designed to do explicitly the opposite, as the intention, for very valid reasons, is to hold and retain water for specific periods of time to control flooding and to potentially retain water on the roof structure for later reuse.

Virtually all the currently available blue roof systems rely on the roof waterproofing and roof drainage system having dual functionality and start from the premise that you are designing a roofing system, when what you should be designing is an attenuation system that is located on the roof.

If you take the view that you are designing a roofing system then there are a number design issues that need incredibly careful consideration, for example the number, positioning, and sizing of roof outlets, roof fall gradient, type of roof construction, and period that water is retained on the roof. With this approach you are designing two opposing functions for the roof which will require design compromise, noncompliance to known standards and accepted best practice, and will therefore increase overall building design risk.

Given the novelty of ‘blue roof’ systems it should not be a surprise that developers and buildings insurers are uneasy siting such attenuation systems above residential developments or critical infrastructure, but this need not be the case if a more logical design approach is adopted.

Unlike a normal flat roof that is visible and open to the elements a blue roof system is often a covered structure that may have hard or soft landscaping above it making it difficult to see if the system is performing. If the system becomes blocked then water will be retained in a semi-permanent fashion if there is not an early warning system, or a regular maintenance regime in place.

Designing for resilience, not only requires compliance with standards but also demands full consideration for worst case scenarios: What if the system is not maintained and becomes blocked, how do we want the roof drainage system to perform in such an instance? What if climate change is considerably worse than has been predicted such that the system regularly overtops, how do you want the system to perform in this situation? These are foreseeable events that require design solutions.

The ACO Solution

The ACO RoofBloxx patented blue roof attenuation system answers these design challenges and achieves this by ensuring that function and form are not confused by creating a separate open attenuation system that sits and operates independently of the roof waterproofing and drainage system.

By creating a separate system, ACO ensures that the roof can drain slowly during the design rainfall events, and to hold water for reuse, but that in extreme and unforeseen events e.g., the system is blocked, or the design event exceeded during storms, that the roof can drain quickly in compliance with all recognised building standards. Most importantly water is not encouraged to remain in contact with the roof waterproofing any longer that accepted design practise allows.

This gives Peace of Mind to designers, developers, insurers and building owners, as the ACO system increases the resilience of the overall roofing structure and therefore eliminates unnecessary risk. Additionally, by separating design responsibility there is a clear demarcation between engineering and design disciplines.

Resilience, sustainability, and net zero are standard watchwords for a new generation of designers that seek to increase the functionality and design life of buildings. Understanding the function of a system is critically important to designing an appropriate solution. The ACO RoofBloxx system enables building regulations and planning conditions to be met and enables a climate resilient system to be installed that helps alleviate surface water run-off and does not compromise the fabric of the building.

To visit our blue roof page please and watch the animation of our system click here

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