Recently there have been misconceptions that certain ‘common solutions’ for concrete-to-steel connections perform just as well as the Schöck Isokorb type KS14 thermal break. This is often not the case. For clarification, an independent investigation into the performance criteria 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 ‘common solutions’ in question being the direct connection of balcony support brackets to a concrete floor slab using no form of thermal break; a solution using brackets in conjunction with a 10mm ‘thermal pad’; and a further connection solution using a thicker 20mm ‘thermal pad’.
The OISD found the Isokorb type KS14 to be a superior thermal insulating element for connecting cantilevered steel components to reinforced concrete; while other comparable solutions failed to obtain the minimum amount of performance required by Part L of the Building regulations.
The first step in the independent investigation determined the heat loss, minimum surface temperature – and consequently the temperature factor (fRSI) – resulting from the use of Schöck Isokorb type KS14 connecting a steel balcony to a concrete floor slab. The temperature factor (fRSi) is used in the UK to indicate condensation risk as described in BRE IP1/06, a document cited in Building Regulations Approved Documents Part L1 and L2. Once established, this calculated performance (1) was then compared with that of the three structurally equivalent ‘common solutions’. The table below presents the minimum surface temperatures and temperature factor (2) for the cases modelled, where the temperature factor used to indicate condensation risk (fRSI) must be greater than or equal to 0.75 for residential buildings.
The Isokorb KS14 unit, with fRSi = 0.904, exceeds these values by some margin and therefore meets the requirements of Building Regulations Approved Documents L1 and L2. Further, the results demonstrate that where no unit is used (fRSI =0.681) and also with the 10mm and 20mm pad connections (fRSI =0.713 and 0.706 respectively) – all three would fail against the criteria required for residential buildings.
Specifiers, contractors, developers and those in procurement need to be wary and question product performance claims involving bespoke solutions. Often they will be found wanting and the lack of transparency in determining true performance values may well mean a product being installed that is simply not fit for purpose. Due to building site ‘tolerances’ it is vital that thermal product solutions should, at the very least, exceed minimum standards and in many cases even that may not be good enough.
As for cost implications, the Isokorb product is ready for installation – there are no ‘add ons’. However, there are possible hidden costs with bespoke versions as it is likely that various bolts, brackets and thermal pads will need to be sourced before installation can be completed. This is complicated further by the possibility that a number of sub-contractors might need to be involved. Just one is required with the KS14.
For your free copy of the report (Reference: 120927SCH – 27/09/12), contact Schöck on 01865 290 890 or email: [email protected]
