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The management of rainfall within the built environment is an important task for the construction industry, with correct and sympathetic source control and attenuation being key to Sustainable Urban Drainage System (SuDS) design.
SuDS demands that water falling across a development site is not simply channelled into storm water drains and discharged into the local river. Instead the drainage is designed to mimic that found in nature where water is attenuated, treated and infiltrated through natural processes. In many cases the Environment Agency is involved in limiting the site discharge through a Limited Discharge Consent Notice, which may be related to the natural drainage rate of 5 litres per second per hectare of site, or lower.
Managing inner city and urban areas
A modern method of source control and attenuation is the Blue Roof, where the roofing system is explicitly designed to attenuate rainwater rather than drain it as quickly as possible, as in traditional roof drainage design.
Blue Roofs can significantly contribute to the SuDS requirements within a development by collecting and temporarily retaining rainfall (for a maximum of 24 hours) within the roof finishes before discharging at a controlled rate. This is particularly beneficial on constrained sites, such as in urbanised areas, or brown field sites, where the use of underground tanks are difficult and/or costly.
A Radmat Blue Roof can be installed at either roof or podium level above the waterproofing membrane or the water flow reducing layer (WFRL) in a PermaQuik or ParaFlex FD inverted application or above an EshaFlex warm roof application. The Radmat Blue Roof will be designed to attenuate water for no more than a 24-hour period from the end of the maximum designed rainfall event. The discharge rate will be calculated to allow the roof to be half empty of attenuated water in a 12-hour period.
Case study: The Forge, Redclyffe Road – London
Telford Homes acquired The Forgein 2014.The site was formerly a bus depot bounded on two sides by existing residential developments. Radmat was engaged together with RMA Architects to design a roofing scheme which would meet the strict attenuation and flow rate requirements imposed by Newham Council. The scheme comprises residential apartments, clustered around communal courtyards, accessed off a new public street with substantial public realm enhancement. The new buildings range from three to five storeys with a 14-storey focal building.
Challenge 1:Meeting the strict run off requirements imposed by the council across a geographically restricted site with reduced height zones. Due to the geographical restrictions of the site and close proximity to neighbouring properties, below ground attenuation had to kept to a minimum leaving the roofs and high level podiums as the key attenuation strategy. Radmat’s Blue Roof scheme had to be redesigned a number of times to meet the stringent attenuation targets even utilising the ‘fingers’ of the roof to maximise the available space.
Challenge 2:High Thermal Requirement, need to attenuate and create Amenity Spaces at roof level. Because the development had to meet high thermal standards and provide as much amenity space to residents as possible while at the same time providing extensive attenuation – the system build ups were considerable and therefore design heights at 
thresholds and parapets were compromised in some areas. A series of inverted PermaQuik hot melt Blue Roofs were specified to provide a robust waterproofing and were supported by BBA certification for both blue roofing applications and an independent durability statement for the design life of the building. In the most challenging areas Radmat proposed its ProTherm Quantum Vacuum Insulated Panel system which enabled the area to meet the thermal requirement in 80% less space compared to standard insulants, while still meeting the attenuation demands. Systems were finished with Radmat’s MedO Green Roofing systems – both fully vegetated blankets for areas overlooked by apartments and seeded biodiverse roofs surrounding the PV panels creating ecological diversity to the main roofs.
Telford Homes chose Radmat Building Products for the following reasons:
- Proven track record as a key account partner both manufacturer and Roofing Contractor
- Radmat’s unique key account service which included scheme evaluation by inhouse architects,bespoke CAD drawings, blue roof calculations
- Products developed for the application including multiple depth blue roof geocells and BBA certified Vacuum Insulated panels to achieve the thermal performance in the limited space
- Systems supported by BBA certification specifically certifying the Blue Roof components and a worked up design so that swift NHBC sign off could be achieved.
Products used in Radmat Blue Roof System:
PermaQuik PQ6100 Hot Melt waterproofing system to main areas
Radmat Geocells, water flow outlet and orifice restrictors of multiple heights and dimensions
ProTherm G insulation 0.13 w/m2k
ProTherm Quantum Pure to overcome reduced height thresholds
Green roofs consisting of pre-grown sedum blanket for overlooked areas and wildflower seeds around PV panels of main roofs
For more information about Radmat Blue Roof systems visit:
https://radmat.com/category/product-data/blue-roof/