Possibilities of Improving the Thermal Protection of Residential Buildings by the Application of Over-Rafter Roof Insulation Systems

The need to save energy, as well as the constant tightening of regulations regarding thermal protection of buildings force the need to look for solutions increasing the thermal performance of building envelopes. One of the important issues in this regard is the appropriate thermal insulation of usable attics. Currently, two layers of mineral wool are most often used - one between the rafters and the other under the rafters. Recently, an alternative solution has emerged, namely PIR (polyisocyanurate) foam over-rafter roof insulation systems. The aim of the article is to assess the legitimacy of using this new method of roof slope insulation. Appropriate conclusions were formulated on the basis of the technical and economic analysis of PIR foam parameters and other insulation materials, and a case study in which one of the actual implementations of the over-rafter insulation was analyzed. It was found that the use of PIR panels as the external insulation of roof slopes gives benefits primarily in terms of improving the quality of thermal insulation works. The over-rafter system is easier to implement than the classical solution (fewer possibilities of assembly errors), and above all, it minimizes thermal bridges. In addition, PIR has a better thermal conductivity than mineral wool, which reduces the necessary insulation thickness, and the possibility of condensation inside the envelope and cold air infiltration is also limited. The barrier to the use of this solution is currently primarily the high price of PIR roof panels, but as shown, the benefits associated with improving the quality of insulation are taken into account and encourage investors to choose such a solution.