Residential complex "Oberfeld"

Benefit: Thermal separation of reinforced concrete walls.
Why better quality does not have to cost more.

Construction that is both high quality and economical - is that possible? The residential complex "Oberfeld" in Boll-Vechigen proves that one does not preclude the other. An innovative energy and insulation concept in which the architect incorporated the thermal separation of reinforced concrete walls for the first time made it possible to optimise this project in terms of cost efficiency, design, and structural stability.

The chairman of the local council called it the "prime asset of Boll". The plot measuring 17,000 m² is superbly located on a south-facing slope with unhindered views across to the Bernese Alps. The bar for this project was very high – in terms of both design, and engineering and physics. Various options were examined together with the local council before opting for the variant comprising 10 apartment buildings with 82 residential units. The planners also paid great attention to designing the surrounding areas. As Andreas Kurth, property developer and architect in one, explained: "We enhanced the land with a building rather than just erecting a building on the the land". He and his team designed the buildings to blend into the slope of the land, necessitating the minimum possible excavation and leaving the lie of the land to literally flow around the buildings. Access for motorised vehicles is entirely underground. The planners paid particular attention to the design engineering details and insulation of the project. Their objective: To create a residential complex that was both high quality and optimised in terms of cost efficiency.

Far better than the Minergie-P-Standard

Despite not being certified and lacking the controlled ventilation that is often a topic of debate, the complex far exceeds Minergie P requirements. The building envelope is approx. 50% below the statutory limits for new buildings as specified in KenV, and approx. 10% below the primary energy requirements specified by Minergie P for building envelopes. According to Andreas Kurth, when it comes to construction quality: "There is probably not much room left for improvement". The thermal separation of the reinforced concrete walls plays a key role. What is so special about it? Thermal separation of brick walls or cantilever slabs, for example, is considered normal practice these days. The procedure is, however, virtually unheard of in reinforced concrete walls. Now the Oberfeld project has shown that such separation can improve the U performance of a building, with façade insulation that is a comparatively modest 24 cm thick yet still complies with the stringent energy standard. "In the underground garage, for example, 5 cm insulation on the underside of the ceiling slab is sufficient, and we didn't need any insulation in the sides at all. That gave us more height and enabled us to create the clean and seamless appearance of the wall surfaces", explained Godi Bärtschi, structural engineer at HSR-Ingenieure. It also eliminated the risk of subsequent discolouration and expensive maintenance of the insulation. In many instances, the thermal separation of components also simplifies the detail engineering of jutties and other design elements, while having a lastingly positive impact on quality and cost.

The courage to implement innovative solutions

HSR examined the structural specifications provided by the manufacturer Schöck with its own 3-D computations. One very important part of this examination was the spot analysis of the thermally separated reinforced concrete walls at the joints to enable them to rule out any risk of structural damage. As architect Andreas Kurth confirmed: "We did of course take a very close look before opting for Alphadock®", especially as it was the first time he and his team had worked with it. "Thanks to our willingness to change our minds, we saved over CHF 50,000 on underground garage insulation alone, and still comply easily with the strict energy standard," At the same time, the reduced thickness of the exterior insulation had a positive effect on the cost of materials and the usable area, thus improving the cost efficiency of the project as a whole.

And what about the structural design, which construction engineers occasionally like to challenge? Both the manufacturer and the property developer Andreas Kurth can alleviate any concerns: "Alphadock®, the product we have used, was developed specifically for this type of application and use. The solid load bearing reserves and intelligent separation design enable easy static calculation and faultless implementation. Added to which, the property-specific proposals developed free of charge by the manufacturer formed the basis for any adjustments to the static design system in collaboration with the engineer."

Conclusion

Anyone looking to build to such architectural and engineering heights does not automatically have to expect exorbitant additional costs. Innovative product solutions such as Schöck Alphadock® not only reduce the cost of materials and production, they also create a larger usable area and thus positively impact both cost efficiency, and the energy, operating and maintenance costs.