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Concrete balconies

Typical residential buildings are supported by concrete frames, often implementing cantilevered balconies made of concrete. Schöck Isokorb® type K is the solution to thermally separate the exterior balcony from the interior slab. Schöck Isokorb® type K offers high thermal resistance by using stainless bars to act as tension and shear reinforcement and highstrength concrete bearings (HTE, high thermal performance) to act as compression modules.

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Figure 12a: Schöck Isokorb® type K for concrete balconies connected to interior slabs.

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Figure 12b: Typical residential building, supporting structure made of concrete. Concrete balconies are thermally broken by Schöck Isokorb® type K.

A modelling study was undertaken by Oxford Brookes University to determine the effectiveness of Schöck Isokorb®. The aim of this investigation was to determine the heat loss, minimum surface temperature and hence temperature factor (fRsi) resulting from use of Schöck Isokorb® type K units, connecting a concrete balcony to a floor slab and to compare these values without the use of connectors (floor slab projecting straight through wall). Calculation was by means of finite difference analysis using BISCO and TRISCO software from Physibel.

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Figure 13a: Wall construction with balcony slab through.

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Figure 13b: Schöck Isokorb® type K50 installed in construction.

Further information about the boundary conditions and the thermal conductivity of the used components in can be found in Reference 2.

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Figure 14a: Balcony connection without thermal breaks: temperature distribution (section). This detail does NOT conform to UK Building Regulations Part L requirements for minimum temperature factor in dwellings (fRsi = 0.75)

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Figure 14b: Schöck Isokorb® type K50 connection: temperature distribution (section). This detail conforms with UK Building Regulations Part L requirements for minimum temperature factor in dwellings (fRsi = 0.75)

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Table 1: Thermal modelling results

Table 1 shows the temperature factor and linear thermal transmittance and equivalent thermal transmittance for the case without an Isokorb unit installed, versus using an Isokorb Type K50. In the UK, the temperature factor (fRsi) is used to indicate condensation and mould risk as described in BRE IP1/06, a document cited in Building Regulations Approved Documents Part L1 and L2. For dwellings, residential buildings and schools, fRsi must be greater than or equal to 0.75.
It can be seen from the results that the Schöck Isokorb® Type K50 unit, with fRsi = 0.91 exceeds these values and therefore meets the requirements of Building Regulations Approved Documents L1 and L2. The results for the case with no unit (fRsi = 0.72) is a failure for dwellings. The heat loss using the Isoborb is reduced by over 40%.

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Figure 14b: Schöck Isokorb® type K50 connection: temperature distribution (section). This detail conforms with UK Building Regulations Part L requirements for minimum temperature factor in dwellings (fRsi = 0.75)