On Overhoeks, Orange Architects provided residential building The Line with a filigree grid in high-strength concrete all around. How exactly is this grid detailed? Architect Jeroen Schipper of Orange Architects gave Architectenweb, sister company of Archello a tour and went into detail as to how the facade was made.
"In Overhoeks, sturdy buildings stand together in high density," begins architect Jeroen Schipper of Orange Architects. " That's why the idea came to us to bring some lightness to it with circular balconies, whose balcony edges would form a filigree grid together with vertical elements. So that the residential building would blend into the neighborhood like a kind of docked cruise ship."
"Because we also wanted to make a stony building, we arrived at high-strength concrete very early on, during the sketch design, and we sought cooperation with Hi-Con," Schipper continues. With the ultra-high strength concrete (UHSB) of Hi-Con balconies can be made with a face of 60 mm. Following this, Orange Architects has also given the vertical elements in their view that size of 60 mm.
The high-strength concrete applied here is provided with stainless steel fibers, which gives it about six times higher compressive strength than regular concrete. Microsilicon has also been added to the concrete, sealing virtually all pores in the concrete. The technical name of the concrete used here is CRCi 2, which allows cantilevers of up to about 3.6 meters to be made. The cantilever can then be 60 mm, although the balcony behind it naturally tapers. This is also the case with The Line residential building, where they cantilever up to 2 meters. At the façade, the balconies are also "tapered," where the concrete bends to the façade plane.
When pouring the concrete, Hi-Con uses wooden molds. When pouring the balconies of The Line, because of their more complex shape, it was decided to use standing molds, so the balconies were poured on their side. In the process, these molds were demoulded from the curved side.
In addition to the steel fibers, which are about 13 mm long, the balconies also have ordinary reinforcement. That makes it easier to calculate with them. And the balconies are also suspended from the main load-bearing structure of the building via that reinforcement.
"With these vertical elements, the balconies transform into verandas of sorts," Schipper believes. "That way you sit just a little bit more sheltered, the balconies are still a little more in line with the house, instead of really sitting in the park between the residential buildings." In doing so, he also finds it interesting that the balconies close in perspective a bit. This has given the building a layered facade.
The vertical elements, which Schipper also describes as "sticks," primarily serve the perception of the building and otherwise have no supporting function. Therefore, they are also suspended from the balconies. Holes in the balconies were prepared in the factory for this purpose. In each hole hangs a screw in a rubber, on this screw hangs a vertical element. Each vertical element has already received a hole at the top for this purpose. On the balcony, the hole is sealed with a round tile. Where the vertical element touches the balcony below, it is fixed with a hook. The holes for this are also prepared from the factory.
Like the balconies, the vertical elements are also provided with regular reinforcement in addition to steel fibers. By the way, the rounded corners of the formwork prevent steel fibers from protruding from the concrete.
Anyone who looks really closely at the concrete grid in The Line will notice that its views are lighter than the concrete behind it. The design process initially assumed production in the Netherlands, where the concrete would be somewhat whiter. Later, when it became clear that production would take place in Denmark, and a sample of it was received, the concrete from that factory turned out to be a somewhat grayer color. Simply because of the slightly different composition of the concrete there. As a compromise, it was then decided to use that light gray concrete, but to give it a whiter coating in appearance. "It's a kind of concrete varnish," jokes Schipper. For the balcony edges, the view is coated, for the vertical elements both the fronts and sides.
Another interesting thing about these vertical elements is that it is precisely the boxed sides that have now been coated, so that the "back" is now not only rougher but also just a different color. Schipper: "The coating thus enhances the effect of those smoother boxed sides versus that rougher back side."
Round holes in the balconies
Like all buildings on Overhoeks - because so prescribed in the urban design plan by Geurst & Schulze - The Line has three setbacks at the top. Within the logic of the filigree grid around the building, balcony edges were created here that no one would walk over. To allow daylight to fall through here and there, Orange Architects designed round holes in them.
"Usually these are then cut out during the design process," Schipper says. "That happened here, too, but a short time later they also came back in, because the extra cost of the recesses did not outweigh the extra material cost." The high-strength concrete used here is about 30-40% more expensive than regular concrete. Thus, the round holes in the balcony edges paid for themselves earlier.
By the way, another interesting detail in the façade is that it does not include any rainwater drains (HWA). "The water just runs off the building," Schipper says. Because of the high density of the material and the fact that it has hardly any pores, the concrete does not pollute much, if at all, and the water can simply run over the concrete. Any contamination can easily be wiped off again. That is at least the theory; it will be interesting to see what the building looks like ten years from now.
"Just as with a coat the outside can be different from the lining, we found it interesting here to give the facade behind the filigree grid a different character," says Schipper. To give that 'lining' a strong vertical line, Orange Architects chose to provide the closed parts in this facade with aluminum T-profiles. These profiles are kept slightly apart from each other, so that an open facade is actually realized