Summer '22

More documents

Recommendations

Info

BLUE ROOFS COMMENT SUSTAINABLE DRAINAGE SYSTEMS & BLUE ROOFS With severe storm events becoming increasingly common, the wider use of blue roofs as part of a Sustainable Drainage System (SuDS) strategy will be crucial for the control of rainwater and flood mitigation. Brian Bell, Head of Technical Services at Marley Alutec, provides an overview of the system, the NFRC’s guidance and what to consider in terms of outlets, drainage and emergency overflows. For urban areas, flooding is a significant issue due to the increased number of hard impermeable surfaces. The impact of climate change will intensify this issue, with statistics showing that extreme weather is becoming increasingly common in the UK. In fact, a Met Office study found that it is now seven times more likely for extreme winter rainfall to take place. Therefore, rainwater solutions must be implemented to address the risk of flooding from urban runoff. SuDS were developed to manage stormwater as close to its source as possible, replicate natural drainage and encourage infiltration, attenuation and passive treatment. The Flood and Water Management Act 2010 requires residential and commercial developments to utilise SuDS to reduce the risk of flooding. The use of a blue roof is one way that a SuDS strategy can be adopted. This Brian Bell, Head of Technical Services at Marley Alutec. is typically designed as a flat roof system and built to temporarily store and release rainfall at a controlled rate. However, as there isn’t currently a national standard for blue roof systems, the National Federation of Roofing Contractors’ (NFRC) ‘Technical Guidance Note for the Construction and Design of Blue Roofs’ should be used for guidance. This image: Marley Alutec blue roof illustration. 28 GREENSCAPE SUMMER 2022 • www.greenscapemag.co.uk
The key feature of a blue roof is an attenuation void in which water can be contained. This is positioned above a waterproof membrane in a warm roof design and above the water flow reducing layer on an inverted roof. Blue roofs are also often combined with green roofs due to the need for a permeable roof surface to capture the water. When designing a blue roof, optimum drainage and discharge should be achieved for effective stormwater attenuation to take place. Establishing the site drainage rate and storage volume capacity are key factors for this. The overall site drainage rate, set by the planning authority, is often defined as the ‘greenfield runoff rate’ and is the rate of discharge if the land was undeveloped. Typically, this is between 5 to 8 litres per second per hectare. The storage volume is how much rainfall the site can hold and then discharge. The standard commonly set for SuDS is the ability to attenuate a storm event with a return period of 1 in 100 years, meaning a storm intensity with an annual probability of 1%. However, the location of the site and type of development may also affect this calculation. In addition, the site must be viewed holistically as the maximum storage volume will also often be influenced by the size of the roof area and the roof’s loading capacity. The NFRC guidance states that for a void depth of 100mm, the water can exert an additional load of 1.0kN/m 2 on the roof structure, which must be accounted for. Number and position of outlets The NFRC guidance also highlights that stored water should be discharged within 24 hours of rainfall. Therefore, the number and position of roof outlets should be calculated to ensure effective drainage and achieve the required run off rate. Some blue roof outlets, such as Marley Alutec’s Elite outlets, feature adjustable flow restrictors, allowing the outlets to deliver various runoff rates and water depths to meet whatever the required rate might be – whether that’s from 0.35 to 5.58 litres per second (l/s) at 25 mm water depth to 0.58 to 9.31 l/s at 150mm depth. Only high-quality outlets should be selected due to their necessary exposure to high water pressure for extended periods of time. Marine grade aluminium outlets offer specifiers increased natural strength, corrosion resistance and overall longevity. The outlet and roof structure should also have a secure connection. Marley Alutec’s Elite outlets feature a membrane compression clamp and high performance butyl sealing ring to ensure a durable, watertight seal. It is recommended to use products that have been tested beyond the predicted requirements to guarantee that unexpected conditions will not lead to a system failure. Finally, the discharge of excess water should be considered. If overloaded, a blue roof can cause water ingress that will damage the roof structure and building. To combat this, outlets can The range of Elite Outlets from Marley Alutec. be used to facilitate emergency water discharge by integrating an overflow into the outlet. However, measures to prevent debris blocking the outlet should also be considered and regular inspections should be carried out to ensure the system is operating as intended. Blue roofs are an effective way to mitigate flooding in urban areas. With the increased likelihood of severe flooding in the coming years, there are manufacturers that can provide key technical support for specifying drainage designs. These manufacturers can also align with wider environmental aims through responsible sourcing and accreditations such as ISO 14001 for environmental management. Find out more about Marley Alutec www.marleyalutec.co.uk/ Tel: 01234 344108 www.greenscapemag.co.uk • GREENSCAPE SUMMER 2022 29
Page 1 and 2: GREENSCAPE Ensuring Best Practice f
Page 3 and 4: GREENSCAPE IN THIS ISSUE... Matt Do
Page 5 and 6: GREENSCAPE SOLAR PV 30 The proven r
Page 7 and 8: Proud to be a member of the GRO Cod
Page 9 and 10: GREENSCAPE UKGBC REPORT REVEALS THE
Page 11 and 12: SUPERIOR QUALITY SOLUTIONS WHATEVER
Page 13 and 14: As a substrate, moves from extensiv
Page 15 and 16: Liquid Roofing & Waterproofing KEMP
Page 17 and 18: NEW VIDEO FROM RAVAGO! Ravago Build
Page 19 and 20: expensive problem to rectify! It fo
Page 21 and 22: Optigrun FKD 25 drainage board - fo
Page 23 and 24: SAVVY SHOPPER THIS AWARD IS PRESENT
Page 26 and 27: GREEN ROOF BUILD-UPS GOING GREEN WI
Page 30 and 31: SOLAR PV RESIDENTIAL SOLAR PV: THE
Page 32 and 33: SOLAR PV RESIDENTIAL >>> Continued
Page 34 and 35: SOLAR PV RESIDENTIAL AESTHETIC APPE

Summer '22

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?