The Chester Balmore project, near Highgate in North London, is part of Camden Council’s community investment programme. It is a project designed to achieve Code for Sustainable Homes Level 4, and the first to be built from scratch by a local authority. Once a 1970’s estate, the previous blocks on Chester Road and Balmore Street were in poor condition and refurbishment simply was not a cost-effective option. Rick Mather Architects developed the project, which is a mixed-use design for around 53 new homes. There are three separate blocks with additional commercial space, making it one of the largest ever residential schemes to meet Passivhaus standard.

To achieve PassivHaus standard, property at design stage must show high levels of insulation with minimal thermal bridges, good use of solar and internal heat gains, plus excellent air tightness. Good indoor air quality is provided by a whole house mechanical ventilation system with efficient heat recovery. The commercial element of the scheme will also be rated BREEAM ‘very good’.

The Schöck thermal break module specified for this scheme is the latest generation Isokorb® for concrete-to-concrete applications – the type KXT. The Passivhaus Institute in Darmstadt has awarded the type KXT with the "low thermal bridge construction" certificate and confirmed its suitability for Passivhaus construction.

A major reason for the superior performance of the type KXT is the thickness of the insulation body. This is increased from the standard 80mm thick to 120mm, providing an even more efficient solution. The type KXT 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. High quality stainless steel bars with improved tensile strength is an integral part of the unit and while the same load-bearing capacity is maintained, there is a smaller rod diameter and therefore a reduction in the thermally conducting cross-section, resulting in a further increase in the heat insulation performance.

Tim Paul from Rick Mather comments: "Balconies offer practical and aesthetic advantages for residents, but they have not always been a popular choice in the context of high efficiency Passivhaus design. However, the advanced technology and superior performance of the Schöck Isokorb® XT range offers such a high level of insulation, that we had no problem in incorporating balcony design into the Chester Balmore project”

John Frankiewicz, CEO from the main contractor Willmott Dixon Capital Works also adds: “As the need to create ever more energy efficient housing to mitigate against the rise in fuel prices becomes more critical, the use of systems like PassivHaus will become more common as the standard for delivering affordable energy housing. Camden is making a very imaginative and exciting statement on delivering low carbon housing that others will be watching closely.”

The Schöck design team has always been on hand to provide specifiers, structural engineers and contractors with a high level of technical support. Additionally, this now includes a discretionary in-house thermal-modelling capability, a service utilised very effectively for the Chester Balmore project.

The type KXT has already seen considerable success in Germany, not least for its sound insulation characteristics. For the first time in Germany there is now a stated minimum standard requirement for balconies. Previously this only applied to covered balconies, but the Schöck Isokorb® KXT 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 remains unique in that it allows connections to be made between concrete-to-concrete, concrete-to-steel and steel-to-steel – and it also provides BBA Certification and LABC Registration. All units meet full compliance with the relevant UK building regulations. The 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 dwellings and residential buildings, 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 re-spectively heat losses through non-repeating thermal bridges. Here, the lambda values of the Schöck Isokorb® enable energy loss in various connective situ-ations to be reduced by as much as 84% to 91%.