Effective Solutions – Structural Thermal Breaks
Schöck Isokorb® thermal break solutions for concrete structures
The most effective way to minimize the heat transmittance of structural components (balconies, parapets, canopies) penetrating the insulation layer is to thermally separate the exterior structure from the interior structure. With the aim of decreasing thermal losses at the connection, structural thermal breaks optimize the function and performance of each integral element at the junction.
The high conductive materials such as reinforced concrete (k = 2.2 W/(mK)) or structural steel (k = 50 W/(mK)) at the connection are replaced with an insulating material of expanded polystyrene (EPS, k = 0.031 W/(mK)) with a minimum thickness of 80mm to give an effective thermal separation. This is non-structural and constitutes the main body and surface area of the thermal break. To conserve the structural integrity between the exterior elements (e.g. balconies, canopies) and the interior structure (e.g. floor slab), reinforcement bars are used to connect both sides and transfer loads (tension and shear). These traverse the insulation body of the thermal break and are made of high strength stainless steel (k = 15 W/(mK)), instead of carbon steel (k = 50 W/(mK). This not only reduces thermal conductivity, but also guarantees longevity through its inherent corrosion resistance. To transfer the compression loads, the thermal break uses special compression modules made of high strength concrete (k = 0.8 W/(mK)), as these offer better thermal performance compared to compression bars made of carbon steel or even stainless steel.
As one can imagine, the heat flow paths through the assembly are quite complex and the resistance to heat flow depends upon how much steel and/or concrete is used per foot, which in turn is also dependant on the loads which have to be supported. For the equivalent thermal conductivity of various solutions see Appendix Chapter.
For a standard balcony, Schöck Isokorb® type CM (k=0.17 W/mK) reduces the thermal conductivity k in the connection area by approximately 90%.
Figure 20B: Placement of Schöck Isokorb® in the assembly. The thermal conductivity of thermal break solutions compared to non-insulated connections is reduced by up to 92%.
The high conductive material of structural steel (k = 50 W/(mK)) at the connection is replaced with an insulating material of expanded polystyrene (EPS, k = 0.031 W/(mK)) with a thickness of 80mm -to give an effective thermal separation of the steel beam. This is non-structural and constitutes the main body and surface area of the thermal break.
Stainless steel is used within the Isokorb® module for the structural elements (bolts and a hollow section) to transfer the loadings, while further reducing the thermal conductivity (since stainless steel k=15W/mK, compared to carbon steel 50W/mK.).
Typically two Isokorb® type S22 are used per beam connection. See Thermal Conductivity of Schöck Isokorb® Thermal Breaks which show the keq and Req respectively. Note that heat transfer through the connection is about 85% reduced compared to the heat transfer through a continuous steel beam.