roof drainage

Adaptability at The Acre: ACO Overcomes Installation Challenges to Provide Sustainable Drainage to Iconic London Building Renovation

Building Products Index Ltd September 25, 2025 Building Drainage, Drainage, Uncategorized Leave a Comment

View the ACO Building Drainage entry on BPindex

When a blue roof was needed as part of a major sustainable renovation at the Acre in London, it was vital that the solution specified could be installed while other work on aspects of the roof were underway. With so many moving parts to the renovation, ACO Building Drainage had to work with contractors to be able to make their usual installation process more dynamic and accommodate unexpected changes along the way.

The brutalist building – previously known as 90 Long Acre, now shortened to The Acre – was built in the 1970s and by 2020 was in need of major renovations to restore its status as one of Covent Garden’s architectural highlights. The 240,000 square foot building would include office spaces, a café, and 113 residential flats. Moreover, once complete, The Acre was to be one of the most eco-friendly developments in the city.

Boosting The Acre’s green credentials meant overhauling several key systems including heating, the electrical supply, and roof drainage. With conditions around the site and the project itself meaning storage space was limited, deliveries had to be carefully planned and ACO’s speedy adaptability proved to be a major advantage. With ACO’s contributions to the project, The Acre went on to be awarded Sustainability Project of the Year by the LRWA.

Commencing with calculations

ACO Building Drainage was invited by building design firm Arup to collaborate on the roof drainage part of The Acre’s renovation. ACO visited the site and provided calculations for the water attenuation the building would need, and recommended products that could provide the attenuation required in line with the overall sustainability goals and planning conditions of the project.

ACO’s calculations accounted for the different sections of roof and the fact that raised areas of the roof drained onto lower parts. The provided 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.

Following the calculations 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.

Unexpected obstructions

Due to limited on-site storage space and multiple aspects of the renovation being carried out simultaneously, only a small portion of the required ACO RoofBloxx could be delivered at a time. To overcome this challenge, ACO communicated closely with Lendlease’s site managers and adapted its usual delivery process to ensure product was at The Acre at the time it was needed. This flexibility was made possible due to ACO’s facility in Shefford, which houses products ready for shipping in cases when short lead-times or sudden changes are a factor.

The main hurdle ACO and contractors from MAC Roofing had to contend with was the unexpected appearance of struts installed directly onto the rooftop to support other building services. These were in place to hold PV panels and screens to block plant equipment from public view to improve The Acre’s visual aesthetic.

The schematic for the ACO RoofBloxx installation had been created before these struts were known to ACO. MAC Roofing discovered their placement when they arrived to carry out the drainage installation. Because of this, designs had to be adapted quickly, while ensuring that the finished product would provide the attenuation needed and prevent any leaks.

Cutting carefully

For each of the more-than one-hundred struts MAC had to work around, pitch pockets had to be put in, the insulation had to be altered, and the ACO RoofBloxx units had to be cut to fit the space available. MAC contractors measured the obstruction, cut the ACO RoofBloxx units to the new size by hand, and then taped and sealed each part individually. ACO provided instructions on how to do this without risking any unwanted water ingress. With each cut that had to be made, the potential for leaks increased, therefore it was vital to the success of the project that the unplanned adaptations were completed to a high standard across all seven sections of roof.

Once the ACO RoofBloxx units were in place, other parts of the renovation meant that pipes and pedestals were placed directly on to the ACO RoofBloxx 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 ACO RoofBloxx’ performance or any aspect of building safety.

Layers and loads

In most blue roof systems, the final ballast weight needed to prevent insulation floating is significant and 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, keeping costs low and project timelines on track.

With ACO’s expertise, 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.

Rowan Gutteridge, Group Director at MAC said: “As with many construction projects, unexpected challenges arise all the time and we work to overcome them. The changes here were bigger than usual and it was in large part thanks to ACO that we were able to complete this installation successfully. When we suddenly had to cut the ACO RoofBloxx to shape, ACO’s expert advice meant we knew exactly how to do it and what adjustments were needed for the installation to make sure everything delivered the desired result. The ACO RoofBloxx units themselves are easy to work with which only helped the project progress. I’m looking forward to working with ACO and its products again on future projects.”

Kevin Bohea, Managing Director at ACO Building Drainage said: “It’s great to see an iconic building like The Acre embracing sustainable drainage. We did hit a few speedbumps along the way so we were glad to be working with MAC Roofing who we consulted with on how best to adapt the installation to the new requirements. Every project has adjustments that need to be made along the way and this one was no different. Quite a bit needed to change while the project was live, but thanks to guidance from our experts and our solutions being easy to use, the team were able to take on the challenge and ensure the installation was completed to an award-winning standard.”

For more on ACO Building Drainage and the roofing solutions they provide, see ACO.co.uk.

Designing climate resilient Blue Roof attenuation systems.

Building Products Index Ltd November 22, 2023 Building Drainage, Drainage Leave a Comment

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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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