Introduction
The introduction of new standards for the levels of indoor comfort required the adaptation of existing buildings. These, in most cases, do not satisfy the required value of thermal transmittance. This has resulted in the development of new strategies for the adaptation of the building envelope, beginning in northern Europe and concerned the adjustment of the energy performance in the case of cold climates. Later on, also for Mediterranean areas, and then in the case of hot climates it became an important strategy to introduce thermal insulation systems for the building envelope. The need to improve the thermal insulation of the building envelope determine a growth of the industrial field based on the production of insulating materials of different origins, for example, the cheaper, but less sustainable, are the synthetic ones. At the same time, it has developed the production of eco-friendly insulating materials. This new materials field could contribute, as well as the use of renewable resources of energy, also to economic development in those countries where, at the present time, these resources are found in abundance but they and are not well used.
The energy retrofit
The energy retrofit consists of all the actions aimed to renovate the existing buildings stock, by adapting their performances to the ones required by current laws. To act on existing buildings means the possibility to choose between different strategies, each that cannot however dispense with proper thermal insulation of the building envelope, the main regulator of the heat exchange between external and internal environment. Among the most common retrofits we can find the following ones:
• Insulation of the building envelope;
• thermal inertia increasing;
• replacement of windows with innovative systems;
• introduction of solar shading devices;
• replacement of air-conditioning systems;
• replacement of lighting systems;
• use of natural sources of thermal energy;
• introduction of renewable energy. Among the systems above, there are methods of intervention that allow to work directly on the building structure increasing its thermal performance, by reducing therefore the use of mechanical systems of air-conditioning. These passive actions, provide above all initials contained expenses, easily amortizable over the short term, thanks to the considerable reduction in energy bills due to their implementation. In recent years, the research and experimentation on the building envelope have spread different kind of materials and technologies, ever more efficient, able to significantly increase the energy efficiency. To insulate the opaque envelope, in fact, allows to contain the main heat losses and to ensure adequate levels of interior comfort for extended periods of time. The choice between the insulating materials changes depending on the case, not only relating to the level of thermal conductivity of each panel, but also to the geographical context and, therefore, the needs which must be meet. Furthermore, such a choice implies that the requirements ever more restrictive than the law now imposes in each climate zone( Italian Law no. 10 of 1991“ Regulations on the rational energy use,
584 ZEMCH 2015 | International Conference | Bari- Lecce, Italy