Going above and beyond

ACO’s sustainable drainage solution for the blue roof of The Acre should have been straightforward, but an unexpected problem meant it was far from plain sailing.

The brutalist building – previously known as 90 Long Acre – was built in the 1970s. By 2020, it underwent a major renovation to become office spaces, a café and 113 residential flats. The 240,000 square foot building was also renovated to be sustainable.

This meant overhauling several key systems including the roof. ACO Building Drainage was invited by Arup to collaborate on the roof drainage. ACO visited the site and provided calculations for the water attenuation the building would need, accounting for the different sections of roof and the fact that raised areas of the roof drained onto lower parts. The calculations also took into consideration the combination of blue and blue green roof that was to be installed as part of the plan to better conserve water, boost biodiversity, clean the air and improve the microclimate of The Acre.

Unexpected challenges

However, complications arose due to the concurrent installation of solar equipment and privacy screening on the same areas of the rooftop where ACO’s RoofBloxx were to be installed. Namely, struts were installed directly onto the rooftop to support PV panels and screens to block plant equipment from public view. The schematic for the installation had been created before these struts were known to ACO. Contractor MAC Roofing discovered their placement when it arrived to carry out the drainage installation. Because of this, designs had to be adapted quickly.

For each of the more than 100 struts MAC had to work around, pitch pockets had to be put in, the insulation had to be altered and the units had to be cut to fit the space available. MAC contractors measured the obstruction, cut the units to the new size by hand and then taped and sealed each part individually. ACO provided instructions on how to do this so there was no risk of unwanted water ingress. With each cut that had to be made the potential for leaks increased, therefore the unplanned adaptations had to be completed to a high standard across all seven sections of roof.

Once the units were in place, other parts of the renovation meant that pipes and pedestals were placed directly on to the units, which was also an unforeseen change. ACO created a new set of structural load calculations to ensure that the components combined with the gravel would not compromise the units’ performance or any aspect of building safety.

In most blue roof systems, the final ballast weight needed to prevent insulation floating is significant – it can impact load calculations, as well as project costs and timelines as delivery and placement of ballast material is factored in. Due to ACO’s patented system, which prevents the floatation of insulation on an inverted roof, only normal ballast weight is required.

Even with the unexpected challenges encountered during the project, MAC Roofing and ACO were able to complete their part of the project successfully, providing The Acre with a sustainable roof drainage system. The complications highlight the need for drainage to be a consideration from the very early stages of any building or renovation project. 

For more, visit aco.co.uk