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'Impartial' comparison is nothing of the sort

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Letters

In an industry noted for healthy scepticism, and highly formalised regulation of both practice and product performance, I was amazed recently to be shown a promotional leaflet purporting to be a serious study comparing the thermal performance of factory-assembled composite claddings and site- assembled twin-skin systems, using thermal imaging or infra-red techniques.

The leaflet presents a rather superficial series of 'comparisons', giving what many will regard as a statement of the glaringly obvious; ie that if the mineral wool and joint details are not applied properly in built- up systems, the result will be heat loss and air leakage. Crikey!

One assumes that the leaflet is in wide circulation and that your readers will quickly draw their own conclusions, but surely few will be deceived by yet another ill-considered, biased attack upon twin-skin or built-up roofing and cladding systems. If these are so comprehensively deficient, as claimed in this last salvo in a long barrage of scarcely credible propaganda, then the wall of silence from owners and users of buildings in which they are incorporated is positively deafening.

More worryingly, the 'comparisons' appear to have been carried out using infra-red thermography to provide a predetermined set of findings, and not impartially as is implied. Briefly, our independent consultants in this field suggest, on the evidence of the published thermographs and study, that:

the clarity of many of the thermograms is low, particularly for a document intended for widespread common reference

they employ broader, less sensitive temperature-range settings for the published thermograms of factory-assembled cladding systems

Much of the information required under iso 6781;1987 (used as the basis for this study) is not given; for example, age of building, date and time of each survey, outside/inside air temperatures and relative humidity, wind speeds, specification of equipment used, etc. (Many of these are critical to the reader in properly assessing the thermal information presented.)

The conclusion was that this study could not be viewed as an impartial nor a scientific examination of the systems in question; the anomalies highlighted should be achieved in undertaking and presenting the findings of an infra-red building survey.

It goes without saying that the leaflet also fails to reveal how the buildings were selected or where they are, nor anything about the relative performance of a properly constructed built-up system in a comparison with a composite system. But then it wouldn't, would it?

M A NEVITT

Marketing manager, Hoogovens Aluminium Building Systems

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