With two dominant diaphragm walls, the house is pushed into the slope. The especially formulated lightweight concrete, with high energy efficiency, does not require additional insulation and exhibits homogeneous wall surfaces of high-quality architectural concrete.
The house, built on a steep slope, confronted the owner and his building contractor with several challenges: The L-shaped lot left only a narrow, restricted construction window for erecting the building between the two adjacent lots.
Thomas Schweigert, Managing Director at the Bauwerk construction company, the building contractor, therefore searched for and succeeded in enthusing a specialist with a particular liking for lightweight concrete in an unusual project: pushing a 210 m² building into a slope, which borders with two parallel diaphragm walls on the neighboring properties. The wide, nearly column-free interior of the building offers a generous feeling for living. On the outer façades of lightweight concrete, it is possible to create homogeneous surfaces of high architectural concrete quality.
Knowhow in matters of lightweight concrete
“In our projects we always want to demonstrate how to build with lightweight concrete,” says Thomas Schweigert, who checks the architectural plans for every construction site for feasibility and efficiency prior to agreeing with the client on implementation. By now, his company has already implemented several lightweight concrete buildings. “On this project we were able to demonstrate our experience once again. As a matter of fact, in the course of implementing several construction projects in collaboration with Heidelberger Beton Kurpfalz GmbH und Co. KG with and Betotech GmbH, we were able to continuously further develop this method.”
First of all, it was necessary to stabilize the ground on the complicated slope site with a complex pile foundation and to brace it with an architectural concrete wall. Then followed the building construction: semi-precast elements, suspended as floor slabs between two canted diaphragm walls, followed the course of the slope. When topped with concrete, the floor slabs, as reinforced-concrete slabs, stiffen the entire structure. On the outside, the upper edge of the floors were cast with concrete in such a way that each diaphragm wall would form a support. The lightweight concrete on the lateral façade is hydrophobized and the precisely executed joint marks the height of the stories. Anchor cones made of concrete plugs indicate at regular intervals where the Peri formwork was previously attached; the pipes for heating and rainwater are installed inside the solid walls.
No additional insulation required
“We can process this lightweight concrete nearly as perfectly and homogeneously as architectural concrete,” as Thomas Schweigert describes the gray construction material with its velvety, closed surface. The surface, despite the expanded clay and expanded glass and a maximum particle size of 10 mm, shows little porosity. The special formulation and the LC 12/13 mix was developed in the laboratory at the company Betotech GmbH Eppelheim under the direction of Wolfgang Eissner. These were accepted by Marek Zwolinski, in collaboration with Manfred Baumgärtner. The thermal conductivity of the 45-cm lightweight reinforced concrete walls of the two solid diaphragm walls is sufficiently low to satisfy the current EnEV for this construction project without additional insulation.
Building contractor Schweigert knows of no other building made of lightweight concrete in the southwest of Germany that was executed with a lambda value as low as this. “For me and my clients, this solid construction method is a genuine alternative to a composite insulation system,” he emphasized. An individual approval by the building authorities was not required for this reinforced concrete building, despite the strict requirements placed for earthquake resistance in the German state of Baden-Wurttemberg.