Study finds stone facades are greener than glass and cost less

Germans Deutscher Naturwerkstein-Verbands (DNV) of Würzburg, Germany, show that using natural stone rainscreen façades rather than glass can considerably reduce the environmental impact of a building in construction, use and over its entire lifetime.

DNV looked at a new office building in Germany, the Opera Tower in Frankfurt, generally considered to be one of the most spectacular German office buildings constructed for many years.

DNV used a lifecycle assessment (LCA) to compare the energy consumption per square metre of typical façade constructions of glass with a substructure of aluminum and a natural stone rainscreen with insulation and concrete backing.

The glass and aluminium facade consumed as much as three times more primary energy in production and use than the stone and the total environmental effects of the glass over the whole lifecycle could be as much as 360% greater.

The thermal protection value (U-value) of 0.32W/m2K for the natural stone façade compared with 1.25W/m2K for the glass façade, so less energy was required to heat and cool the building with the stone façade.

DNV say the cost of the completed stone façade was k640/m2 in production and k4.50/m2 in maintenance – which is half as much as the glass.

In real life a façade does not use all stone or all glass, of course, but DNV calculate that architect Christoph Mäckler’s decision to use a natural stone façade with glass rather than all glass for the 6,000m2 of façades on the Opera Tower will produce annual energy savings of 23% – that’s 1,800 tonnes of carbon dioxide saved a year.

It has helped the Opera Tower to become one of the first office buildings in Europe to achieve a Gold Standard under the American LEED Green Building Council scheme.