Recently, we discovered a website about the calculation of the U-value of different configurations. The website works in German and only the introduction can be red in English.

This website, between the many U-value calculators, is very interesting for the following reasons:

• The website is developed by Ralf Plag, a physicist working on elementary particles with an interest in building physics. He can be considered as a neutral person, which will not favour a particular material.
• Not only the U-value is calculated but also humidity issues and, very important, summer heating. Indeed, we all know that a room under an insulated (light) steel roof with rather low U-value can still be unpleasant warm in summer.

For this we took the example of a U=0.15 W/m2K roof, insulated with cellular glass. In one case, we insulate with 27cm ZES cellular glass (0.042 W/mK) and in the other case, we use 35cm GLAPOR cellular glass. Although a 0.15 W/m2K roof functions in both cases well in winter, both configurations perform very different in summer. For both cases, we show the shift of the temperature wave and the amplidude reduction as calculated by the site.

GLAPOR directly foamed from recycled glass

ZES cellular glass foamed with special glass composition

We observe that the cellular glass, directly foamed from recycled glass (GLAPOR) has a 80% larger amplitude reduction and a more interesting phase shift compared to cellular glass, foamed from a special melted glass composition. It is clear that both configurations behave the same in the winter but that the GLAPOR roof behaves a lot better in the summer. On top of that, GLAPOR  cellular glass has a cheaper production process (no melting of a special glass) and is for that reason more ecologic.