Polyurethane rigid foam has a useful life of 50 years and more, and maintains its very low conductivity over time, due to its closed cell structure and ability to withstand external impacts such as moisture ingress or air movement.
Although there is usually a slight increase in thermal conductivity as the material ages, this is taken into account in the declared lambda (such as may be found in the CE mark), which represents an average value over the expected lifetime of a building – a minimum of 25 years.
Two samples of 28 and 33 years were extracted from a pitched roof and a flat roof, respectively. The tests conducted by an independent test institute demonstrated that the specimens showed no damages, no holes, bubbles, cavities or other inhomogeneities. The testing institute confirmed that, after 28/33 years in application, these PU insulation boards were fully functional and still reached all declared values and performances.
A flat (or low slope) roof is often exposed to dynamic mechanical loads e.g. by pedestrian traffic or small vehicles. These loads occur during construction of the building or for regular maintenance of installations on the roof. After a few loads some materials tend to lose their compressive strength, resulting in a deeper imprint of e.g. the foot on the waterproofing.
The stress in the waterproofing may lead to cracks, or to penetration of a mechanical fixer through the waterproofing if the imprint is close by. Therefore the insulation material and the waterproofing may be severely damaged, resulting in a leaking roof. In contrast to some fibrous insulation products, PU is unaffected by foot traffic and loading incurred in the course of normal maintenance.