A £14.4m three-storey PFI Extra Care complex at Knowsley, Merseyside, is benefiting from the use of innovative off-site manufacturing that integrates Schöck Isokorb structural thermal break units with the Hollowcore system. Bluebell Park Extra Care Facility homes are being built for Knowsley Housing Trust, part of the First Ark Group. It is the Trusts largest Extra Care development to date and there are two blocks on site. The first provides 101 single and two-bedroom Extra Care apartments for rental; and the second, 21 two-bedroom apartments made available for purchase through an Older Persons Shared Ownership scheme.
Many of the apartments feature spacious balconies, so the prevention of thermal bridging is critical. Quite apart from heat loss, condensation can lead to structural integrity problems and worse, encourage mould growth, which has health implications for residents, in the form of respiratory problems and dermatitis. One of the most effective countermeasures on the market is the Schöck Isokorb structural thermal break. These units dramatically reduce thermal energy loss in connective areas and enable inner surface area temperatures to remain well in excess of those likely to cause mould formation and condensation.
The Isokorb type KS14, for concrete-to-steel connectivity, is being installed at Bluebell Park, in conjunction with the Hollowcore floor system. First the precasters broke out selected cores and cast reinforcement bars in their works. Then the KS14 thermal breaks were fixed to a template matching the broken out Hollowcore. The complete modules then supplied to site, dropped into position and the broken out Hollowcore filled with insitu concrete.
The Hollowcore has voids extending its full length, so there is a huge weight saving over floor slabs of equal thickness or strength, resulting in both transportation and material cost efficiencies. With the slab sizes being typically 1.2m wide x 4m long, they are also faster to install and provide an immediate working platform for following trades.
The Hollowcore system is certainly beneficial, but the Isokorb type KS14 also has its own verifiable performance values. It provides BBA Certification and LABC Registration and comfortably exceeds the requirements of BRE IP1/06 and Part L of the Building Regulations. Here the temperature factor used to indicate condensation risk (fRSI), must be greater than, or equal to, 0.75 for residential buildings, which is comfortably exceeded by incorporating the Schöck product.
In some areas of the UK marketplace, certain common solution alternatives for concrete-to-steel connections are claimed to perform thermally just as well as the Isokorb type KS14. To clarify the situation, an independent investigation concerning the effectiveness of steel balcony connections to concrete slabs, was carried out by the Oxford Institute for Sustainable Development, at Oxford Brookes University. The aims of the investigation were firstly to determine the heat loss, minimum surface temperature and hence temperature factor (fRSi) resulting from use of Schöck Isokorb type KS14 units connecting a steel balcony support to a concrete floor slab. Secondly, to compare the calculated performance with that of structurally equivalent solutions. In the test all three alternatives to the Schöck solution failed against the criteria required for residential buildings (1).
Specifiers, contractors, developers and those in procurement therefore need to be wary and question any product performance claims involving bespoke solutions.