commARCH (Commercial Architecture), January/February 2020

Thermal breaks prevent condensation improve thermal comfort reduce energy demand The design team averted thermal bridging issues at the balconies by installing Schöck Isokorb Structural Thermal Breaks Positioned within the building envelope between the interior floor slab and cantilevered balcony slab they act as continuation of the wall insulation through the concrete floor slab Most of the cross sectional area typically consisting of concrete and carbon steel is now comprised of a high performing graphite enhanced expanded polystyrene block that is less than 2 as conductive as concrete Additional energy savings are derived from the modules stainless steel rebar which is one third as conductive as its carbon steel equivalent Projecting from both sides of the structural thermal break the rebar is engineered to fully develop into the adjacent concrete components without the need for lapping onto adjacent steel The assembly provides the necessary strength and stiffness to support the anticipated loads on the exterior cantilevered slab while raising the temperature of the adjacent interior slab by up to 34 º F 19 º C with three results 1 prevention of condensation and mold growth on adjacent interior surfaces 2 improved occupant comfort and 3 energy savings up to 90 percent at the connection The Sparks five balconies contain a total of 148 linear feet 44 linear meters of structural thermal breaks Joe Lopera says the thermal breaks worked well with the post tensioned concrete structure allowing for the 10 ft 3 m long and 12 in 305 mm thick balcony slabs to freely cantilever for a more elegant building Structural thermal breaks gave me more freedom as a designer he adds Underside of slabs reveal The Sparks post tension concrete construction supporting 10 ft 3 m cantilevered balconies commARCH 20 Stainless steel tension and shear rebar of Isokorb structural thermal break ties into carbon steel rebar of interior and exterior slabs prior to casting Early planning led to success The architect structural engineer contractor and structural thermal break supplier conducted early planning and design meetings to determine the best way to install and integrate the structural thermal breaks with the post tensioning layout Eric Lewis project manager with J H Findorff Son Inc Construction of Madison and Milwaukee said This was a first time experience with Schöcks structural thermal break technology But the modules became easy to install after the pre planning and design meetings with Schöck as well as their site visits and instructions and guidance to our crews at first install Lewis added that the structural thermal breaks allowed us to pour the deck and the balcony in the same day improving the overall schedule The thermal breaks eliminated the need for the usual edge forms that create the joint where the deck joins the balcony slab saving time and materials to prep the balcony slab after pouring the main deck and letting it set up enough to strip the form which is the typical sequence Eric Feile of Pierce Engineers a consulting structural engineering firm based in Milwaukee said Theres always the danger of elements like structural thermal breaks being value engineered out of the project But we fought for them and they stayed a part of the project