Durability of continuous roofing

As part of the national research project on durability, the Naples research unit addressed roofing subsystems. Roofing is one of the most complex (insofar as normally comprised of numerous materials) components of the external coverings of buildings. Probably the area which has traditionally presented the main maintenance problems, it’s also the one which presents most variety across, and within, its different contexts of application. Another – but certainly not the last – problem which needs to be addressed is “quality of execution”, a particularly sensitive issue in the roofing sector, which in fact remains one of the few remaining building trades still generally entrusted to specialized firms, without whose expertise the results in terms of performance often leave much to be desired. In the course of our analysis of the state of the art in the durability of continuous roofing – which included both scientific literature and an examination of Italian and international standards for laboratory testing – it became apparent that - as with so many other building components - while indications on individual products are in plentiful supply (e.g. membrane), there is something of a black hole when it comes to the built-up roof itself – and in fact it’s the latter which is particularly interesting, as it’s in the variety of materials which comprise them, and the diversity of the ways in which they’re combined, that lie the reasons for the problems which can often lead to sudden performance decay and anticipated death. The fact is, here as in other parts of building, we have to acknowledge that the physical changes undergone by roofing materials during and after their application are decisive for their performance evaluation: returning to the example of prefabricated bituminous membrane (a good example after all, since in a sense it’s a crucial component in the appraisal of the performance of the roofing assembly as a whole), this is a material which as prescribed in the standards is tested in such a way as to ignore the changes it undergoes subsequent to its application at temperature using propane gas; likewise ignored are the differences which manifest themselves over time in accordance with the different protection systems currently in vogue in the country: nowadays acrylic paint instead of slate granules. Then there are other important factors: the articulation of the different layers of the built-up roofing, the presence or absence of an insulating layer, the nature of this layer: these are all of major significance in the evaluation of roofing life cycles. We felt, therefore, that it would be useful to go a little beyond the strictures of standard prescriptions. Although standards are an obligatory point of reference for a whole range of conditions, they were of little use when it came to designing the samples to be subjected to accelerated ageing if the ultimate goal of laboratory testing is re-scaling to real conditions. In other words: in agreement with the other offices, a research approach driven by accelerated ageing testing on the different materials ultimately leads to re-scaling due to externally-sourced sampling. All very well, but if this was to have any bearing on real buildings, i.e. the behaviour of the elements undergoing testing as part of a complex as well as individually, all the more reason to design samples capable of reproducing as faithfully as possible the situations and conditions of the same materials in real buildings