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Deutscher Naturwerkstein-Verband e.V.

Natural Stone – the balance looks right

Facades of natural stone show remarkable energetic advantages in comparison with glass facades. This is the result of an extensive study that compares facades of natural stone and glass.

Experts consider the Frankfurt Opera Tower to be the most spectacular German office building in years. After having done extensive research and technical investigations, the prestigious architect Mäckler and the building company Tishman Speyer favored a facade of natural stone to one of pure glass for reasons of energy efficiency. Because of its natural stone facade the Opera Tower received the coveted gold status of the LEED rating system of the U.S. Green Building Council as one of the first office buildings in Europe.

Developers, architects and users are becoming increasingly aware of the enormous consumption of energy that goes along with the construction and maintenance of glass facade systems. Politics and the media have focused on these issues various times. The Bavarian Supreme Court of Audit issued a recommendation in 2008 to use glass facades only in especially justified circumstances. Already in 2004 the German news magazine „Der Spiegel” (no. 47) pointed out that the necessary air-conditioning of glass buildings is responsible for skyrocketing energy costs.

The German Natural Stone Association (DNV) took a growing interest in energy-saving facades as an opportunity to have carried out a sustainability study to assess the natural stone and glass facades in terms of their environmental and economic performance. The consulting company PE International, a global player in the field, agreed to conduct the study.

The three-part study includes a complete life-cycle assessment of natural stone as well as glass facades, investigating the properties of glass and natural stone regarding production, use and recycling (End of Life). The study also compares different methods of facade construction in respect to their use of primary energy and their impact on the environment. Economic considerations of façade models with different glass content complete the study.

During the buildings' period of use some building materials have to be renewed or substituted. The life cycle of building materials is determined by the Manual for Sustainable Construction issued by the German Federal Ministry for Construction. This manual stipulates an average life cycle of 80 years for natural stone. It should be noted that the stipulated life cycle is only an estimate and does not preclude a notably longer life cycle.


Life Cycle Assessment- Content

This study is based on the LCA-method (LCA – Life Cycle Assessment), which systematically analyses a product's effects on the environment during its entire life cycle (from the cradle to the grave). This includes the product's effects on the environment during production, during its period of use and during its disposal as well as upstream and downstream processes (e.g. raw materials and supplies).


Life Cycle Assessment – Part 1

The first part of the study analyses the environmental impact of two typical facade designs, carried out with natural stone and with glass, over a period of 100 years. One square meter of a back-ventilated natural stone facade with heat insulation on reinforced concrete is compared to a coextensive facade of glass mounted on a substructure of aluminium.