54 HPM 0816

HPM-08-AUG-2016

54 SUSTA I N A B I L I T Y & WAT E R S AV I N G High rise challenges As more people squeeze into our city centres, there is a distinct trend towards high-rise living, which places heavy demands on a building’s drainage system, argues Mike Rawlings, Arecent report revealed that more than 250 buildings higher than 20-storeys are being planned for London, with most providing luxury flats for young professionals. This trend is mirrored in other cities around the UK with three quarters of those living in the centre being in a flat or apartment. Often these residents are affluent young professionals who are paying a lot of money to live close to their work and other amenities. With restrictions on space it seems that many developers are seeking to build upwards and, according to estate agents, young professionals are keen to live in high quality tower blocks with a high level of comfort such as, air quality, space and silence – well above the noise from pedestrians and traffic. High rise pressure However high, high rise living will get, what cannot be argued is that it will place an immense strain on a building’s drainage system. And with a typical lease being 99 years on most flats, it will have to stand the test of time. Consider a blockage on a lower floor. As more wastewater enters the pipes from other users, water pressure throughout the system will rapidly increase. This will cause issues with maintenance personnel finding the source of the blockage and rectifying it. As an industry, should the pressure requirements for drainage in tall buildings be revisited? At the moment, soil systems in the UK are generally required to operate at 0.5 bar, but if there is a blockage on the lower floor of a tall building the resulting pressure could be significantly higher. This will ask serious questions about the strength and pressure resistance of the pipe material and its joints. For buildings of this height, specifiers of above ground systems would generally choose between cast iron and high-density polyethylene (HDPE). With a good jointing system, HDPE will typically operate up to 1.5 bar pressure, with the best performing cast iron systems capable of operating up to 5 bar of accidental pressure with standard ductile iron mechanical joints fully restrained, or even up to 10 bar accidental pressure with the addition of grip clamps. This has long been recognised in commercial buildings where cast iron drainage systems tend to be the material of choice. The consequences of maintenance, or worse even having to replace the system, is extremely disruptive, so lifetime costings of different systems need to be taken very seriously. Silence please High rise flats and apartments in high quality developments also raises the importance of silent drainage pipes, particularly at the most acoustically sensitive points in the system such as, offsets in the pipework or at changes in direction. When it comes to the noise attenuation of different drainage systems, then it really pays to read the small print. A specifier needs to ensure that they are comparing like for like. While BS EN 14366:2004 sets out test criteria for measuring noise in waste water systems, many manufacturers infer lower levels by including dB levels in a product’s brand name. You need to watch out for this marketing trick, because the level inferred in the title is measured at a much lower flow rate of water than the test demands. In addition, it is a growing opinion among consultants that BS EN 14366 does not go far enough when considering acoustic levels. Most noise within a pipe system comes from offsets in the stack and changes of directions through bends, yet the standard only measures water flowing through a vertical pipe. There is also a question about what the optimum flow rate should be, the standard stipulates four litres per second (l/s) for the most common diameter 100mm. This is important not just because it affects the final customer’s satisfaction with an installation – people do notice noisy pipes – but also because the UK code of practice BS8233 does set criteria for sound reduction in different types of buildings. These state that structure born noises, from equipment behind the room must have a maximum noise level of 30dB(A) in the main rooms of a residential property and a maximum level of 35-40dB(A) in other rooms such as kitchens or offices. It is also worth noting that the dB scale is not linear, so a system that is just 4dB higher is actually twice as loud as its quieter alternative. You can reduce this noise through vibration transfer by using special pipe clips and clamps, enclose the pipework within a mass of 15Kg/m2 or lag the pipes with 25mm unfaced mineral fibre, as described in Building Regulations Doc E. This, of course, all adds to both installation time and costs. Perhaps the simplest answer is to use the quietest material you can for the pipes. Again, cast iron proves to be the quietest material for drainage systems. Independent research undertaken in Holland demonstrated that cast iron was 7–8 dB(A) quieter than acoustic plastic based systems in areas that generate the most noise, for example, where there are offsets and changes in direction. Fire safety Finally, if there is a fire, then cast iron is non-combustible, will not fuel the fire or emit dangerous smoke and will probably remain intact. Plastic on the other hand, will burn with certain materials like HDPE, also dripping molten droplets potentially propagating the fire to lower floors and, depending on the plastic, will give off toxic fumes or sooty smog, which are widely recognised as the biggest killers in any fire. Building upwards is an obvious answer to the demand for city centre living, but it does place a strain on a building’s services. Currently eight of the top ten tallest building in the UK have cast iron drainage systems, the most recent being the Shard and the Walkie Talkie in London. While plastic is often the material of choice for domestic and smaller commercial premises, cast iron drainage systems, with all of its benefits, strength and longevity, offer the best solution for both high rise working and living. marketing manager for Saint Gobain PAM www.hpmmag.com August 2016 enquiry number 138 The Shard, one of the UK’s top ten tallest buildings, features a cast iron drainage system “However high, high rise living will get, what cannot be argued is that it will place an immense strain on a building’s drainage system”


HPM-08-AUG-2016
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