In 2022 the Irish city got its first blue roof, a sustainable drainage system that temporarily stores rainwater and releases it slowly to control flooding
Architects are facing growing challenges as flooding and stormwater get harder to manage in urban environments.
Blue roofs temporarily store rainwater and slow its release. Despite the name, they are not roofs at all, but distinct attenuation systems that sit on top of a roof and function separately.
This distinction is important because the standards for traditional roofs promote the fast removal of rainwater, while blue roofs retain water for specific periods to control flooding and also enable water reuse.
To design blue roofs effectively, the following must be considered from the outset:
- the number, positioning and sizing of roof outlets.
- roof fall gradient.
- type of roof construction.
- the period that water is retained on the roof.
By treating blue roofs as separate systems, architects can mitigate risks and ensure compliance with all relevant standards and regulations.
ACO’s RoofBloxx system at Chelmsford Road apartments, Dublin
In 2021 Clonvara Developments wanted to redevelop a city centre residential building on Chelmsford Road in Ranelagh. Under new planning policies introduced by Dublin City Council, the project required a blue green roof to obtain approval.
ACO Building Drainage and Beton Construction Services collaborated on its design and installation using ACO’s RoofBloxx system.
A key part of the consultation was ACO’s assessment of the hydraulic requirements, which were based on a one-in-100-year rainfall event, with a 20 per cent uplift for climate change.
Following the assessment, ACO specified an attenuation system that was installed on an inverted blue roof and covered a catchment area of 131.8m2.
Beton used its MasterSeal 2103 coating system as the roof waterproofing membrane, ensuring the concrete roof slab was completely sealed and watertight.
To insulate the roof, a Ravatherm XPS 300 SL lining was fitted, along with a separation membrane. The ACO system, which doesn’t rely on the roof waterproofing to act as an attenuation liner, greatly reduces risk and prevents possible buoyancy of insulation and potential reduction in the building’s U-values.
When rain falls, it is captured in the open top tank and discharged slowly via a flow restrictor at 0.28 litres per second into the perimeter gravity drainage system.
In extreme circumstances, any excess rainfall can bypass the attenuation system through internal overflows and into the roof outlets. A total of 240, 85mm-thick RoofBloxx units were used, providing 3.77m³ of stormwater storage capacity.
Besides storing and slowing the water down to prevent flooding, the blue roof helps with other functions - cooling for the building in summer, providing amenity and biodiversity and reducing the urban heat island effect.
By fully understanding the positive impact blue roofs can have on urban developments, architects can design effective and compliant systems that enhance urban resilience. The Dublin project shows how innovative design and collaboration can lead to successful implementation, providing a model for future, more sustainable projects.
Find more on this case study at aco.co.uk/chelmsford-road
For more information and technical support, visit aco.co.uk
Contact:
01462 810400
abdtechnical@aco.co.uk