ENVIRONMENTAL AND ECONOMIC IMPACTS OF NATURAL STONE AND GLASS FACADES
30-10-2018
New considerations in architectural design
In the 2000s, Opera Tower in Frankfurt was one of the first office buildings in Europe, to be certified to the LEED (Leadership in Energy and Environmental Design) Gold standard. The highest category of the international energy efficiency rating system is partly due to the fact that as a result of the detailed examinations and modeling carried out in its design phase, the building has been constructed partially of a natural stone facade instead of the entire glass facade, thus improving its overall lifecycle energy use and ecological effects.
This spectacular project has drawn even more attention to the fact that energy consumption play a growing role in case of new and existing buildings which strongly influences the investment and long-term maintenance costs of the buildings, in addition to the environmental aspects,
Energy need and environmental impacts
A comprehensive study of the German Natural Stone Association (DNV) and the PE International consulting company has analysed the lifecycle energy consumption, harmful emissions and cost-effectiveness of conventional back-ventillated natural stone facades and glass facades. During the investigation, the prosecces of production and construction of building materials, the operation and maintenance of the building, and the demolition/recycling phase were taken into account.
According to the study, the energy consumption of the traditional back-ventillated stone facade (with 50% window ratio) is less than one third of the glass facade (ca. 1800 MJ/m2 < 6300 MJ/m2).
At the same time, the negative effects on the environment also differ significantly. The traditional natural stone facades are significantly lower in terms of global warming potential (GWP), acidification potential (AP), ozone depletion potential (ODP), eutrophication potencial (EP), ozone-smog potential (POCP), with an average load of only 35-75% compared to glass facades.
Cost efficiency
Lower energy demand is naturally reflected in the expenses: the values of the back-ventillated stone facades are considerably better from cost-effective point of view. One of the main reasons is the lower heating requirement, since the heat transfer coefficient of the back-ventillated stone facade is significantly lower than that of the glass facade (0,32 W/m2 <1,25 W/m2). While the energy requirement of natural stone facades is approx. 100-150 KWh/m2 per year, in case of glass facades it is 300-700 KWh/m2/year (source: Institut Wohnen und Umwelt, Darmstadt). In addition to cost-efficiency from energy consumption, the other decisive factor is that investment and maintenance costs are significantly lower in case of stone facades: the investment and maintenance costs of a conventional back-ventillated natural stone facade with a traditional 50% glass surface are only half as compared to facades with almost complete (90%) glass surfaces. Of course, with the decrease in the ratio of glass surface, the deviation decreases proportionally.
If we look at the total cost over the 50-year timeframe for the two types of facades – which includes the investment, maintenance and operating (energy use) costs - the result is 40-50% more favorable for a building with natural stone facade. This follows logically from the fact that there is a significant difference in expenditure both in terms of energy use and investment+maintenance. Overall, according to the research the facades with natural stone covering have significant benefits both ecologically and economically in the examined time horizon.
Sustainable development with the support of architecture
As an extreme energy-intensive sector, the construction industry can play a decisive role in supporting sustainable development if "green buildings" are widely used in architectural concepts and investment decisions. Today, around 40%-60% of the lifecycle energy consumption of buildings comes from the production and installation of the building materials, and 25-40% from the heating and cooling demand. Using natural stone facades we are able to contribute to sustainable architecture in both areas, thanks to the low production energy demand and low thermal conductivity of natural stone facade panels. The rational use of natural stone facades can greatly influence the classification of a building as "green" according to the international standards.
(Source: Deutscher Naturwerkstein-Verband e.V. - www.natursteinverband.de)
