The inverted roof has its water proofing membrane under the thermal insulation. On the contrary, a cellular glass roof has in principle this membrane on top of the thermal insulation. For example GLAPOR cellular glass blocks are “swimmed” in hot bitumen to get a vapor (and water) tight system. This is nicely shown in the following YOU TUBE movie.

And indeed, the water proofing membrane is the weak point in the construction. UV-light and large temperature variations are causing the rather short life time of the membrane. In case of a leak, not visible inside, freeze and thaw on the cellular glass will damage irreversibly the roof in a few months over a large thickness.

On top of that, some cellular glass insulation becomes rather expensive when a large thermal resistance is requested, which is the standard today.

The inverted roof with XPS does not know these problems. Current producers are DOW, BASF and KINGSPAN. But this roof has another possible problem. During rain fall in the winter, cold water may reach the water proofing membrane, cooling the structure under the water membrane proofing. This may induce condensation inside if the structure is not very heavy. For this reason, BASF, synonym for German quality, requests to have a minimum thermal resistance  of 0.15 m²K/W.

This thermal resistance is already availbale with 1cm GLAPOR PG700 cellular glass but 4cm is needed to have enough mechanical strength for installing. For just 6€/m² extra material cost, you have the best of both worlds.

1. An absolute protection against humidity problems inside
2. A very well protected water proofing membrane
3. A huge thermal insulation with cheap XPS without any problem possible

6€/m² or less than 600€/m² for a 200m² house (one stock) is giving you absolute protection against humidity with a cheap very well insulating inverted roof, with its never to replace water proofing membrane.

Indeed, this is the inverted roof reinvented or the best of two worlds: CG + XPS (CG = cellular glass; XPS = extruded polystyrene). It is the conviction of BELGLASCZ that the combination of different thermal insulations is giving you the best systems.