Aluminum , wood, PVC. Three materials that are profoundly different in origin, production processes, performances and design solutions, each of which boasts large groups of supporters who, considering the technical, economic, ecological and aesthetic aspects each time, pronounce on the alleged superiority of one respect to the other. In recent years, studies, and the resulting assumption of alleged advantages to be weighed commercially, have opposed each other and those who expected the confirmation of their theses – or at least the denial of those of others – from the study “ Sustainability assessment of windows and curtain walls ”certainly were disappointed by the final report of the research: none of the materials analyzed demonstrates a clear supremacy. But precisely this result allows us to focus attention on the undoubted methodological value of the study, to underline some fundamental aspects related to the sustainability of windows and transparent envelope systems.

Commissioned by the European Aluminum Association , the research was carried out by the German engineering company Drees & amp; Sommer Advanced Building Technologies , in collaboration with PE-International , an organization of sustainability experts.

The study, conducted in Germany and published in January 2015, takes its cue from the observation that the studies available so far on the subject do not analyze how the type of material that makes up the load-bearing structure of the frames affects the performance of windows and facades. Consequently, the researchers evaluated the sustainability aspects of types considered “standard”, namely:

• double-leaf and single-leaf windows (residential building) using frames in aluminum , wood, wood-aluminum and PVC;
• portions of structural facade with mullions and transoms (office building) using profiles in aluminum , wood and wood-aluminum.

The first part of the study dealt with the assessment of environmental and economic impacts. Here are the steps of the methodology used:

• calculation of thermal comfort and energy consumption, by means of a thermal simulation software, for each of the two different climatic zones considered (Berlin and Rome);
• calculation of the economic cost of life cycle (LCC) according to ISO 15686-5;
• life cycle assessment (LCA) according to ISO 14040 and EN 15804.

In the second part, the overall sustainability performance of the various window and curtain wall systems were compared with a quantitative methodology, based on the criteria of the Deutesche Gesellschaft für Nachhaltiges Bauen (DGNB) and the Green Building Rating Scheme (GBRS), including: environmental impact, economic quality, social quality, technical and process quality.

In fact, according to the main building sustainability protocols, the building envelope is a fundamental component in the overall environmental assessment as it contributes on average 10% to the sustainability of the entire building. The assessment was based on sustainability criteria derived from EN 15643/1 (Building life cycle stages), widely used in Europe in the real estate sector.

The relative phases are as follows:

• comparison with environmental certification protocols of building sustainability (only for the part relating to windows and facades);
• in-depth development of a set of indicators to assess the sustainability of different materials.

Since holistic evaluation identifies a large set of indicators (including sensitivity analysis), the research focused on the most relevant scenarios for the evaluation, in order to provide reliable results. Finally, the research was submitted to leading industry experts in order to understand their views and criticisms.

THE PHASES IN DETAIL

In a nutshell, here are the evaluations resulting from the analyzes listed above and detailed in the 80 pages that make up the study.

Energy aspects

The comparison of performance in terms of comfort and consumption of thermal energy required during the operating phase did not show substantial differences between the various materials. In general, the differences in terms of performance are the result of the different dimensions of the profiles used and, in the same climatic zone, the variations found did not exceed 1.5%.

Economic aspects

According to the Life Cycle Costing, PVC windows for residential use show a lower investment and operating cost than other materials. Aluminum is the best among the materials considered