Opinion International rescue?
The selling of building drainage codes globally is causing more harm than good in the public health arena, but an answer may be at hand, says Peter White
to design the drainage. This is due to the codes of Europe, the US and Australia being sold internationally. It isn’t unreasonable to expect some variations to reflect local custom and practice, and this wouldn’t be so difficult if they more or less all said the same thing, but they don’t – far from it, especially where venting and building height are concerned.
W In his latest book, Transient Airflow in Building Drainage
Systems, John Swaffield, emeritus professor and former head of the School of the Built Environment at Heriot- Watt University, compares the five major codes used internationally to design the drainage for a 20-storey residential block. These are: BS EN 12056-2:2000; AZ/ NZS 3500.2:2003; ASPE DATA book; Uniform Plumbing Code; and the International Plumbing Code. What Professor Swaffield found was that the documents all recommend different solutions, particularly in terms of vent stack requirement and size, the requirements for which range from none to 125mm.
This rather suggests that some of the guidance may be
a little wide of the mark, but the question is whether or not it is recommending under- or over-design. The latter is, of course undesirable, but the former risks expensive post- construction problems.
These various codes have all arrived at different design solutions for two reasons; the first is because codes have evolved on the basis of translating what is observed to work at the time into sets of rules – rules that become more and more detailed in response to the increasing complexity of systems. The second is because codes are written by committees, and the nature of committees leaves them prey to the influences of special and local interests. ‘Okay,’ I hear you say, ‘so if the codes are all based on
what works, then where (or what) is the issue?’ Well, if you are using the local code in its home country and designing something similar to the schemes that provided the experience on which the code is based, you are not going to go far wrong. But if you use BSEN 12056 to design a 100-storey tower in the Middle East, you have to ask yourself how much
52 CIBSE Journal September 2010
hen working on international projects, one of the first things you are likely to notice is the plethora of local and international codes according to which we are required
experience of similar ‘working’ buildings informed the code. I would argue that the ‘well, they all work’ approach is risky if it isn’t tempered with some consideration of the ‘home’ zone from which a particular code has evolved and the type of buildings on which the code is based. Perhaps an even greater risk is when you are presented with several different international codes. Do you choose the one that you feel is most relevant, the one that is least onerous, or cherry pick the bits that suit you best from each? Obviously only one code
The ‘well, they all work’ approach
should be applied. However, the temptation to use more than one is enticing, because some of what is written in the codes is nonsense. For example, the maximum 10-storey implied restriction on the use of air admittance valves (AAV) in BS EN 12056 is arbitrary. It was based on the fact that the largest hydraulic rig available for BBA testing was – you guessed it – 10-storeys! Of course, if future codes were to be based on set design parameters and analysis as opposed to what is observed to work, codes would become interchangeable, because the laws of physics don’t change from country to country. The good news is that this may not be too far off. Heriot-Watt University has developed a computer simulation called AIRNET to model individual system behaviour, which could be used to inform the basis of a future code. AIRNET has already been used to develop the positive air pressure attenuator (PAPATM
) device. This, in conjunction with AAVs,
can be used instead of traditional venting. PAPAsTM
are currently being retrofitted to various
international projects that are experiencing problems with drainage ventilation. I would speculate this is due in part to the inappropriate application of existing codes – hopefully something that will no longer be an issue with the next generation of codes. l
Peter White is public health principal at consulting engineers, Hoare Lea.
is risky if it isn’t tempered with some consideration of the ‘home’ zone from which a particular code has evolved
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