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The use of insulating elements to block thermal bridges is a recent innovation in the UK. B&E talks to Schöck about how architects are rethinking the way they insulate balconies.

BALCONIES and other cantilever construction elements, which project through the building envelope and break the insulation layer, are notorious for creating thermal bridges. Heat escapes at a much higher rate than the adjoining areas and the result is significant heat and energy loss.

When the outside temperature drops, the connection point of the cantilever element inside the building will also experience a dramatic temperature decrease, leading to the formation of mould and condensation. The mould formation appears first, as its formation temperature is approximately 3°C higher than the condensation temperature.

Mould growth is known for being a health hazard, and is one of the major sources of respiratory allergies such as asthma. Sustained exposure of the walls to condensation will also lead to serious plaster and paintwork deterioration.

There are two types of thermal bridges: Geometric thermal bridges, in which part of the structure projects through the building envelope, and material thermal bridges where materials with different conductivity are used in combination. In the case of non-insulated balcony slab connections, heat is lost due to the ‘cooling fin’ effect of the balcony slab and the thermal bridge which is created due to materials with good thermal conductivity protruding through the insulated façade. The non-insulated balcony connection is one of the most critical thermal bridges in the building envelope.

Thermal bridging modules have been used in mainland Europe for a long time, although. the first in the UK were provided for the Eden Project by Schöck in 1999. The construction industry has since considered them as a means to comply with the changes to the Building Regulations.

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Thermal break modules are innovative, high performance thermal break modules designed to help architects, designers, structural engineers and contractors meet Part L. Due to their thermal insulation properties, thermal break modules dramatically reduce thermal energy loss in connective areas by guaranteeing the homogeneity between cantilever structures and the internal floor.

They also transfer load and maintain full structural integrity, while at the same time keep inner surface area temperatures well over those likely to cause mould formation and condensation.

The modules work by blocking the flow of heat with a good insulation material, such as a plastic. Schöck has developed a thermal break, which, consists of a polystyrene core supported by load-bearing stainless steel rods.

Passing through this polystyrene core are stainless steel bars. The bars take the tension and shear forces between the building frame and the balcony. The bridge also includes a compression module, which is made of a concrete-like material, reinforced with microfibres.

Thermal break modules differ from traditional methods and can be as simple as putting expanded polystyrene insulation on the underside of the soffit. Contractors put insulation on the soffit of the balcony, and 1.5m along the ceiling of the inside room.

However, a cold area can track back from the outside of the building, along the ceiling and to the edge of the insulation. The building can have been finished and inhabited for a few years before the problem presents itself.

The Oxford Institute for Sustainable Development, at Oxford Brookes University, recently carried out a series of tests on the thermal performance of steel beam junctions using different connection methods, and one of the methods.

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The purpose of the investigation was to determine the heat loss, minimum surface temperature and temperature factor and equivalent conductivity, resulting from using thermal break units connecting a steel I-beam, and to compare those values with alternative connection methods and with a continuous beam.

The results showed that the two thermal break units achieved a thermal performance of 0.82 and 0.81 respectively, which exceeded the values of BRE IP1/06 and met the requirements of Building Regulations Approved Documents L1 and L2.

As buildings get taller, it looks like balconies will play a greater role in meeting our needs for space, both at home or at work. Revisions to Part L make it tough for the construction industry to adopt these new designs, while at the same time meeting targets for energy efficiency.

However, through adversity comes innovation, and manufacturers and suppliers are showing that they can think outside the box to find ways to help reduce the UK’s CO2 emissions through novel means of preventing heat loss.

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