Cantilever Slabs at Stairways and Shafts

Normally cantilevered slabs and edges are considered extensions of the floor or roof levels of a structure. Often times however, conditions require a connection along vertical walls or areas where interiors floors are omitted because of stairways or mechanical shafts. These areas have the same potential problems with thermal bridging since there is an interruption in the continuous insulation layer.

For this Design Break, we explore details of a project in which Isokorb® thermal breaks were used in just such conditions, 15 Leonard Street located in the Tribeca neighborhood of New York City.

Structural plan showing the forces required along the areas where the balcony will be supported by Isokorb® structural thermal breaks. The areas along the openings will not have any structural support. However, they will remain thermally isolated from the outside wall of the building.

Here, the structural connections are shown in the background while in the foreground the slab opening is boxed out. Schӧck Isokorb® type CM modules terminate as they go beyond the complete slab. Schӧck provides “filler blocks” to continue the needed isolation. The filler blocks are designed at the same height and width of the Isokorb® and they include fire boards on the top and bottom to maintain the fire proof layer which is included in all Isokorb® modules. In this detail, the foam fillers are tied down to the formwork and will be cast into the space between the balcony and the beam running along the wall.

This image shows the opening for the adjacent stairwell and also the mechanical shaft which is just behind. The filler modules (provided by Schӧck) are used for all areas where the slab cannot run continuous.

Schӧck Isokorb® is visible along the exterior insulation layer. At the door openings the top cap of the modules will be covered by door sills (typical detail).

Schӧck Isokorb® is a safe and effective solution for all applications – even where major portions of the connection zones have no structural support. Schӧck engineers will consult with your project team to find the most efficient solution and give the designers one less thing to worry about!!