Window Wall Detail at Balcony / Slab Connectionfrom Adam Kimble
Every balcony, penetrating the building envelope with scenic window walls, has three main issues to be addressed: thermal bridging, forces at the balcony/slab connection, and water intrusion. The Schöck Isokorb® Type CM is the effective solution for these obstacles, reducing the heat flow from the inside to the outside, while also conserving full structural integrity.
Therefore reinforced concrete at the connection is replaced with an insulating material, expanded polystyrene (EPS), to give an effective thermal separation in the slab. This is non-structural and constitutes the main body and surface area of the product. To conserve the structural integrity between the exterior balconies and the interior slab, high strength stainless reinforcement bars are used to connect both sides and transfer loads (tension and shear). These traverse the insulation body of the product. This not only reduces thermal conductivity up to 70% compared to carbon steel, but also guarantees longevity through its inherent corrosion resistance.
Special compression modules (HTE High Thermal Efficiency modules) are used in the bottom to transfer the compression loads. The HTE module is made of 17,000 psi high strength steel and poly propylene fiber reinforced concrete. The combination of high strength concrete, small section area and low thermally conductive materials again offer advanced thermal performance in comparison to carbon steel and stainless steel.
The combination of all these aspects means that the Schöck Isokorb Type CM reduces the thermal conductivity at the connection by approximately 90% compared to traditional reinforced concrete connections.
This effectively contributes to improve overall R-values of the building envelope and saves operational energy costs. The utilization of Isokorb benefits the occupant by reducing the potential condensation buildup with the possibility of mold at the connection and increasing occupancy comfort.
One of the biggest issues to overcome in a balcony/slab connection is developing a drainage detail to stop any water intrusion. Typically, to prevent water intrusion, a detail is comprised of a step down from the interior slab to the balcony. A step down can vary from ¼” up to 3” dependent upon the preference of the architect. .
This can be achieved by the Schöck Isokorb® Type CM for smaller transitions up to 1″.
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For larger step down balconies Type K-HV can be utilized.
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For transitions higher than ¾“ with exterior sliding doors ADA compatibility should be considered.
These two Isokorb products provide options for architect’s design preference on detailing the step down for water intrusion prevention, while also ensuring structural integrity and thermal efficiency.
Visit the Schöck North America website for more information about structural thermal breaks for concrete and steel connections. Explore the full range of Isokorb® products for balcony, canopy, steel beam, exposed slab edge, parapet and rooftop connections.
Considering structural thermal breaks for an upcoming project? Have a Schöck Engineer call you to answer your specific design questions.