BRE Report (BR) 443 Conventions for U-value Calculations is a document produced by the Building Research Establishment in the UK. As its title suggests, the report details best practice that should be followed by anybody carrying out U-value calculations for building elements.
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‘Declared thermal conductivity’ is the lambda value of an insulation product as it leaves the factory. In the context of inverted roofing, ‘design thermal conductivity’ is the lambda value of the insulation once it has been adjusted for potential moisture absorption.
When calculating the U-value of an inverted flat roof, the thermal conductivity of the insulation layer should be the product’s design lambda value and not its declared value. Because of the insulation’s position above the roof waterproofing layer, it is expected to be exposed to some rainfall and therefore a moisture correction factor should be applied accordingly.
High compressive strength thermal insulation for inverted, green and blue roofs.
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High compressive strength thermal insulation for residential and industrial buildings.