Many cities throughout the world are looking for ways in which to cope with population growth, whilst curbing energy consumption and environmental impact. And the unlikely focus of international interest currently is the historic city of Heidelberg, in south-west Germany. Residentially it is very popular and commercially it is very successful, but Heidelberg has an expansion problem. There is barely any property to be had in the city’s picturesque old town, or along the banks of the River Neckar, and if anything does become available, the prices are on a par with those of Munich, in the region of €5,000 or more per square metre.
The spectacular solution is to build a completely new district – the Bahnstadt – on a 286 acre area that was once home to Heidelberg’s now defunct rail freight and marshalling yards. The €2 billion initiative is claimed to be the largest single passivhaus development in the world; and when completed in 2022 it will provide living space for some 5000 residents. There will be a vibrant mixture of culture, education and employment, with around 7000 jobs created, particularly in the life sciences and communication technology sectors. All buildings, not just the 2500 residential properties, will meet advanced passivhaus standards, requiring only 10% of the energy of a conventional building. There are green roofs with only a small number of solar panels, large windows on south facing aspects and small windows to the north. To meet any additional heating needs a mainly wood chip district heating network with “mini-net” distribution will serve the entire district. The energy supply is 100% renewable and Bahnstadt will be the biggest single site in Europe in which the “smart meter” concept is applied throughout, providing each household with an overview of consumption and costs. In terms of energy efficiency, the new district by far exceeds national legal requirements as set out in the current Federal Energy Saving Ordinance, with consumption less than half that of traditionally constructed buildings. Motorised traffic will be mainly subterranean and every building will be equipped with an underground car park and include charging points for electric cars and e-bikes. Cycling is being promoted heavily as the prime means of transport.
Balcony connectivity used to be a problem with passivhaus construction
One of the key criteria for apartment living anywhere in the world these days, not least Bahnstadt, is the aesthetic and practical requirement for the inclusion of balconies. However, with the demands of high insulation levels and the prevention of thermal bridging being critical elements in passivhaus design, the incorporation of balconies has not necessarily been a popular choice with designers. However, the development of the Schöck Isokorb type XT structural thermal break unit has played a major role in resolving that particularly challenging connectivity issue.
Schöck, a specialist in the provision of advanced solutions for thermal energy structural insulation, is best known for its range of structural thermal break units. And its latest generation product for concrete-to-concrete applications – the Isokorb type XT – offers such a high level of insulation that the Passivhaus Institute in Darmstadt has awarded the product with the “low thermal bridge construction” certificate and confirmed its suitability for passivhaus construction.
Thousands of type XT units are being incorporated into the Bahnstadt development and the major reason for its suitability is the thickness of the insulation body, which is increased from the standard 80mm to 120mm. As a result the unit not only improves thermal insulation performance by up to 30% in comparison to to the standard range, it also improves impact sound insulation by around 50% as well. A further reason for the superior performance of the type XT is the HTE module, a pressure bearing block made of steel fibre reinforced high-performance concrete with Kronolith, a titanium ore aggregate from Kronos Titan. The unit offers architects and engineers a variety of design options and there is even the capability to construct stepped height balconies, with increased fire protection also taken into account, as the HTE module offers fire-resistance class F 120. High quality stainless steel bars are also an integral part of the unit. Although there is a smaller rod diameter, the tensile strength is improved and the same load-bearing capacity is therefore maintained. This means a reduction in the thermally conducting cross-section, and an improvement in the heat insulation performance.
Before the Bahnstadt project, the Isokorb type XT had already seen considerable success in Germany, not least for its sound insulation characteristics, as there is now a stated minimum standard requirement for balconies. Previously this only applied to covered balconies, but the XT has the advantage that it conforms to the minimum requirements for impact sound protection – without any additional floating flooring on the balconies or covered balconies.
The Schöck Isokorb range allows connections to be made between concrete-to-concrete, concrete-to-steel and steel-to-steel – and in the UK, all units meet full compliance with the relevant building regulations, while also providing BBA Certification and LABC Registration. There is a requirement described in BRE IP1/06 – a document cited in Building Regulations Approved Documents Part L1 and L2 and Section 6 in Scotland – that the temperature factor used to indicate condensation risk (fRSI) must be greater than, or equal to, 0.75 for residential buildings and this is easily met by incorporating the Isokorb.
In addition, there is also compliance with the Government Standard Assessment Procedure, SAP 2009, concerning CO2 emissions from buildings and respectively heat losses through non-repeating thermal bridges. Here, the lambda values of the Schöck Isokorb enable energy loss in various connective situations to be reduced by as much as 84% to 91%.
For your free copy of the Schöck Specifiers Guide and / or the Technical Guide contact the company on 01865 290 890 or visit www.schoeck.co.uk