over, such as resin bound paving. Cellular paving is a rapidly expanding paving option due to its relatively low cost and simple installation process requiring minimal specialist tools and its low skill installation process.

Due to the simple installation methods, most cellular grid structures are available as supply only or supply and installation by the manufacturer/retailer. This allows onsite contactors the ability to complete the installation along with any other groundworks and landscaping before specialist teams come in to complete the final surface course works. An example of when a cellular grid structure was the perfect solution to a project that required a permeable paving solution but had issues with access was on an installation at St Peter’s Church, in Battersea, London.

The project involved the resurfacing of an enclosed courtyard and footpaths as part of a larger regeneration project of the whole building. The brief was to provide a permeable, low maintenance, attractive surface that could be enjoyed all year round by the members of the church community.

Blue roof design considerations after BS 6229:2018 update


igel Blacklock, technical director at Bauder, and Chris Roddick, green and blue roof product manager for

Bauder, discuss the changes in the BS 6229:2018 update that impact rooftop water management solutions.

Chris, tell us about Bauder’s rooftop SuDS system, BauderBLUE Chris: BauderBLUE is a blue roof system which attenuates heavy rainfall and controls its discharge over a 24-hour period to tackle standing water and flash flooding in built up areas.

How will the revisions in BS 6229 update impact the design considerations for a BauderBLUE roof? Chris: The 2018 update clarifies and reinforces the meaning of a zero falls roof used in most blue roof systems. A zero falls roof is defined as having no more than a

1:80 fall, but more importantly the roof must not have any back falls away from outlets. This will mean all back falls must be corrected with localised latex screed or additional outlets.

Nigel, what structural considerations are required when thinking about zero falls on a blue roof? Nigel: A detailed structural analysis of the deck should account for construction tolerances, settlement and deflection under load with a concrete slab level survey carried out to identify any back-falls prior to the waterproofing being installed. Hence the advice “design a fall of 1 in 80 to achieve not less than zero”, starting at zero inevitably will lead to back-falls.

How does the thermal performance update apply to a blue roof? Chris: The U-value achieved in an inverted roof greatly depends upon the amount of

water that passes through the joints of the insulation and sits on the waterproofing, as this will cause rainwater cooling. This has a negative effect upon the roof insulation value. Nigel: There is now a note that suggests

that not less than 10 per cent is added to the thickness of the insulation to take account of rainwater cooling. However, water on an inverted blue roof might sit on the waterproofing for longer and with a greater depth, BS6229:2018 states no correction factor should be used which will lead to much thicker insulation than is currently used. BauderBLUE is supplied as part of a full

Bauder roofing system and therefore has a single point warranty.

0845 271 8800 Access into the courtyard was

restricted due to a low overhanging arch and pillars, meaning traditional sub base options such as tarmac or concrete were inappropriate. This meant the SureCell cellular grid structure could offer would provide the permeable sub base solution they required.

The surfacing works were completed in June 2018 and included the supply and installation of both the cellular grid structure and the resin bound paving. Another benefit of using resin bound paving as a permeable surfacing solution is the wide range of colours and creative design possibilities that it allows. For this project there was a requirement to differentiate the pathways and steps from the open courtyard area so two natural aggregate blends were chosen, a lighter shade for the courtyard and a darker shade for the paths and steps – which also matched the walls and brickwork of the courtyard.

Duncan Andrews is marketing communications manager at resin bound permeable paving manufacturer SureSet



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