Raising The Roof: First Ever Blue Green Roof in Dublin Constructed with ACO’s RoofBloxx System

With new planning rules to abide by in Dublin, the developers of a commercial three-story residential apartment building had to demonstrate that its scheme would have a blue green roof to obtain planning permission. ACO worked together with Beton Construction Services to design and specify an innovative blue green system that would manage stormwater runoff, improve resilience, and be the first of its kind in the city.

In 2021, Clonvara Developments set sights on redeveloping 47-48 Chelmsford Road in Ranelagh, County Dublin, into a residential apartment building. However, as part of new planning policies introduced by Dublin City Council (DCC), the scheme would need a blue green roof so it could be granted planning approval.

Under DCC’s Green Blue Roof Policy, all new developments with roof areas exceeding 100m2 need a blue green roof, which are recognised with helping reduce the risk of flooding, help mitigate climate change, whilst providing amenity and biodiversity. DCC also identified that these multi-purpose roofs would be critical in a city like Dublin, where much of the land is already built up and space for sustainable urban drainage systems (SuDS) is limited.

This is where Beton Construction Services (Beton) and ACO Building Drainage (ACO) joined forces to create the first ever blue green roof in Dublin. Beton is a leading subcontractor in surface protection services in Ireland and was brought in by SCD Consulting as a nominated specialist contractor on the project to design and install the blue green roof. ACO provided consultation for the design of the blue roof attenuation system including hydraulic calculations and rainfall event modelling, and supplied its patented RoofBloxx system to form the blue roof attenuation tank that sits on top of the building’s roof.

Creating a waterproof roof

A key part of the consultation was ACO’s assessment of the hydraulic requirements, which was based on 1 in 100-year time series rainfall, as well as accounting for a 40% uplift in climate change. Following the assessment, ACO specified its RoofBloxx attenuation system to cover a catchment area of 131.8m2, installed on an inverted blue roof.

Introducing the ACO solution to an inverted roof separated the competing drainage requirements. By engineering an elevated shallow structural attenuation system that operates independently of the flat roof drainage system, it allowed the roof to be engineered to known standards and best practice, without compromising the ability of the roof to drain quickly in extreme circumstances.

Beton used its MasterSeal 2103 coating system as the roof waterproofing membrane, this guaranteed the concrete roof slab was completely sealed and watertight. To insulate the roof, it used its Ravatherm XPS 300 SL lining, along with a separation membrane.

As the ACO system doesn’t rely on the roof waterproofing to also act as an attenuation liner, it greatly reduces risk, and in the case of an inverted roof system, it 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 l/s and then into the perimeter gravity drainage system. In extreme circumstances any excess rainfall can bypass the attenuation system through internal overflows and at the perimeter of tank and into the roof outlets.

A total of 240 85mm-thick RoofBloxx units were used to form the blue roof, stacked together in two layers and providing 3.77m3 of stormwater storage capacity. A 10mm drainage layer was used to create the structural drainage layer that the lined open top attenuation tank sat on.

Dan O’Connor, Business Development Manager at Beton, led the project and said: “When we were approached about this job, we knew we’d need guidance from blue roof specialists. We turned to ACO because we know they not only have innovative products like the RoofBloxx system, but they have the knowledge, experience and assisting tools to make sure that the job runs smoothly. With ACO’s support, the project was swiftly granted planning approval, and we and the developers have peace of mind that the roof is protected for years to come.”

Sean Drudy from SCD Consulting commented: “When we were appointed for this project on Chelmsford Road, we did some quite extensive technical and research appraisals of blue roof systems available on the market. We specified the ACO RoofBloxx system for the project in conjunction with Beton Construction Services Limited as the installation company, as both companies and their systems came with excellent reputations. “We were very happy with the end result and found the technical design and documentation offered along with the installation and performance on site to be to a first-class standard.”

Going green

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, as well as reducing the urban heat island effect.

Meanwhile, the water held in the attenuation tank helps irrigate a green roof made from a layer of sedum carpet. This roof provides greenery on top of the building, attracting wildlife and promoting biodiversity in the inner-city area. Additionally, the plants contribute to reducing CO2 and enabling the roof and building to be better for the planet.

Neill Robinson-Welsh, Consultant for ACO, said: “We are proud to have partnered with Beton on the first ever blue roof in Dublin. Managing and caring for water will only become more important as the issue of water resilience grows. It’s fantastic to see that Dublin City Council has put planning controls in place, and thanks to our collaboration with Dan and the team at Beton, we have constructed a roof that performs multiple functions, ensuring sure that rainwater is not only slowed down but also put to good use.”

For more about ACO Building Drainage and the RoofBloxx attenuation system, visit www.aco.co.uk/products/roofbloxx

For more about Beton’s MasterSeal Roof 2103 Spray Applied Waterproofing system, contact Beton Construction Services www.beton.ie Tel: Dublin +353 1 4016402