Temparature Rises in Insulation Debate
Testing the effectiveness of insulation is notoriously difficult. Mark Brinkley reports on the merits of laboratory vs field testing.
The world of thermal insulation is well used to professional rivalries and knocking copy, but a current spat between rival manufacturers threatens not merely competing products but the whole system of third party accreditation which underpins construction innovation in Britain.
At the heart of the dispute is the claim by the French firm Actis that it's top selling product, Tri Iso Super 9, a reflective multifoil only 25mm thick, is equivalent to 200mm of mineral wool. This claim, substantiated by BM Trada and thereby widely accepted by building control and the NHBC, is hotly disputed by manufacturers of competing products and now one of them, Celotex, has commissioned independent tests which it hopes will disprove it.
Behind the dispute lies a battle for the future of roof insulation. As the thermal regulations become ever tighter, designers and builders have been struggling to accommodate the necessary insulation within the roof fabric. Mineral wool is now rarely used because it's simply not efficient enough to give a sufficient U value within the rafter void. Foam board manufacturers, principally Kingspan and Celotex, have been benefiting hugely from the legislative changes but have also found that they have been loosing market share to reflective multifoil insulation.
Richard Crisp, marketing director for Celotex UK, said: "We became acutely aware that sales of Actis and other multifoils were growing. If it works as advertised, then we would like to be making it or, at least, selling it. So we set out to see if it was as good as it claimed to be." Celotex paid for samples of the Actis to be independently tested by the National Physical Laboratory in Teddington. There, it was subjected to the standard test for thermal insulation, known as the guarded hot box test. To be equivalent to 200mm of mineral wool, the R value measurement would have to have been around 5.0: in fact, Actis scored just 1.7. Used in a roof application, this would give a U value of between 0.5 and 0.6, whereas the latest Part L requirement is much lower, at just 0.2.
The NPL labs results were in line with test data from Germany, Canada and the USA for reflective multifoils. So how has Actis managed to achieve acceptance in the UK market and why have BM Trada seen fit to give it their stamp of approval? The answer lies in what is being tested and the relative importance of conduction, radiation and convection.
Actis claims that the guarded hot box test looks principally at rates of thermal conduction whereas their product works by stopping other channels of heat loss, principally radiation, convection and unplanned ventilation. They prove their product by building comparison roofs and measuring the heat loss from each. If a roof insulated with Tri Iso Super 9 can be shown to perform to the same standard as one built with 200mm of mineral wool, then the thermal characteristics must be equivalent. Actis last undertook such test in 1997. It was verified by BM Trada who checked the design, construction and the test data and subsequently gave it their stamp of approval.
On the back off this one test, multifoils have been given the green light to sell into the UK market as being equivalent to 200mm of mineral wool. Other multifoil manufacturers have only to prove themselves to be as good as Tri Iso Super 9 for them to be accepted. One such, YBS Super Quilt, has even used the National Physical Laboratory to show "a 13.7% better performance than its nearest competitor" without publishing what the actual test results are.
During the next 12 months, Part L is due to be tightened again. The multifoils are faced with another hurdle, for it will no longer be enough to be equivalent to 200mm of mineral wool. Rather, it is believed that the new standard will be around 250mm of mineral wool. Actis already have a new product in production, known as MultiPro TS 250, and testing is underway to show its performance characteristics. It's essentially the same product but with eight reflective layers instead of six. Industry watchers are awaiting the test results with interest, but few are anticipating anything different to the previous tests.
www.insulation-actis.com (site in French)
Housebuilder's Update background:
Insulation: the murky science
Ever since thermal conductivity rates were first measured and compared, there has been debate about just how relevant they are. It is accepted that heat moves through the building fabric via four different methods, conduction, convection, radiation and ventilation, and also that the more complex the structure, the more difficult it is to model what is happening within it. There is also likely to be a huge discrepancy between laboratory results and as-built performance, similar to what has been found with sound insulation designs. The regulatory authorities accept laboratory measurements as gospel: there is remarkably little post-completion testing carried out, if only because a whole building is such a complex system that it's impossible to isolate the effect of one particular component.
The field is therefore open to anyone who can show that their product performs as well as, or better than, a competitor.
Reflective multifoils are being sold as the answer to every roof builder's problem: how to build in really good insulation levels without having to deepen the roof profile. They hardly rank as an innovation, having been around for decades, but until recently they were always seen as being too expensive compared to the wools and foams which builders more normally work with. But with Part L demanding ever increasing depths of insulation, multifoils have come into their own and are they are now taking an increasing market share.