An example of a roof that is well
suited to rooftop attenuation. Even with BS compliant falls, some
ponding is common due to building tolerances and workmanship
water, Polypipe, for example, has developed and tested versions of its siphonic outlets that can give accurate reduced discharges for a range of flow rates. Another option is to run small-bore pipework down
the building with a standing head of water in them and install an in-line flow control device located in a plant- room or somewhere similar on a lower floor, where maintenance can be undertaken safely. The performance of any control device must be
demonstrable to the sewerage undertaker, Environment Agency or other authority that has set the outflow restriction. As with all rainwater disposal designs, the most
important factor is to correctly assess and design out the risk of ingress into the building. Overspill points from the roofs to protect against blockage of the outlets or a storm in excess of the design parameters are critical. In theory, if these are provided and the flashings and tanking details are robust, there should be no additional risk of water ingress using a blue roof as opposed to more traditional approaches. The rainwater designer must also check that all
penetrations through the roof have been adequately detailed so that the reservoir is not breached at any point. An explanation of how the roof is designed to perform should also be included in the building log
Blue roofs: some key design elements
Adequate overspill points or overflows must be provided to ensure water ingress to the building is prevented in the event of blockage or rainfall above the design parameters
Waterproofing upstands to be increased to cater for potential additional water depth
The design depth of water will depend upon the outflow restrictions, the chosen return period for the storm and the available storage area
The roof membrane performance and application must be discussed with the manufacturer at the time of design
There will be some residual water retained in slab undulations potentially requiring designated walkways for safe access
> The Society of Public Health Engineers
The CIBSE Society of Public Health Engineers (SoPHE) was set up to provide a higher profile and focus for public health engineering, and a route to gaining professional status. Public health engineers contribute greatly
to social welfare, with particular regard to facilities such as water, drainage, gas and fire engineering systems in a large range of applications. This important input is long established and essential to provide clean drinking water supplies and adequate
sanitation and drainage facilities. Over the last few years, water conservation has also grown in importance, forming an important part of the drive for sustainability in homes and offices. SoPHE aims to promote the art, science
and practice of public health engineering, along with raising the awareness of the contribution engineers make to this sector. Through organised technical talks, evening events and newsletters, members are kept informed of specific developments
and relevant updates on legislation, as well as having the opportunity to network with colleagues. It also organises the annual SoPHE Young Engineers Award, encouraging young engineers of the future. The society has also created an Industrial
Associates forum for leading manufacturers working within the public health industry. Through the society members are able to input into CIBSE publications and government consultations. To find out more about joining, visit
www.cibse.org/sophe
Most of these details will ultimately be the responsibility of the architect to detail but will require guidance and co-ordination from the rainwater disposal designer
www.cibsejournal.com
September 2010 CIBSE Journal
45
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