Inverted roofs are one of the most challenging applications for thermal insulation products, as the structure will always have moisture in the form of both water and water vapor, large pressure differences, frost stress when wet, and a certain degree of load. The most common inverted roof structures include parking areas on the roofs of shopping centers, roof terraces, and green roofs. Depending on the application, the surface structure on top of the thermal insulation will consist of poured concrete, coarse aggregate, fine aggregate and tiling, or dirt/soil and ground vegetation.
In addition to the usual tests, the requirements specified for products used for inverted roofs according to ETAG 031 include freeze-thaw-resistance testing, water absorptivity with diffusion, and long-term compressive strength, i.e. compressive creep test for a period of utilization of at least 25, but preferably 50 years. These tests are used to verify the longevity of the utilized products and that their thermal insulation properties remain unchanged in demanding conditions. These tests are the most stringent ones in use and have all been conducted on Finnfoam, proving that its thermal insulation and compressive strength properties remain unchanged.
Today, our technical support is also often approached with questions regarding the use of FF-PIR polyurethane insulation products in inverted roof structures. Polyurethane is not the right material for applications where the product is subjected to moisture stress. The reason for this is that polyurethane is always partially open-celled, and the cell structure is very glass-like. Additionally, its long-term compressive strength (approx. 2 metric tons/m2) is relatively low, which allows it to gather water under moisture stress and thus prevents the structure from working as designed.
The ETAG 031 for inverted roofs also does not consider PU insulations as a suitable material, as the applications of polyurethane include dry, i.e. regular, wall and ceiling structures. For inverted roofs, the one and only product with suitable longevity is XPS, or Finnfoam, which has also passed all the above tests required by ETAG 031.
Insulation installation (a grooved panel (FI-400 URA) on the underside with the grooves facing down, a grooved panel with the grooves facing up on top)
|Filter cloth or diffusion film|
Installing the covering (tiling, shingle, soil, etc.)
An inverted roof of a shopping center used as a parking area. Insulation from 80 mm FI-400/URA (one layer) and FL-400 (two layers) panels.