Thermal Breaks

Avoiding thermal bridging is critical with balcony design detailing

Building Products Index Ltd June 24, 2021 Thermal Breaks Leave a Comment

Thermal images of a residential building with higher temperatures at the windows, doors and balconies

A thermal bridge is a localised area of the building envelope with significantly higher thermal conductivity than surrounding areas. Cantilevered balconies are the most critical thermal bridges and their presence results in a higher heat transfer out through the building and colder surface temperatures on the inside. The main consequences are higher energy consumption, non-compliance with Building Regulations and condensation. The latter leading not only to structural integrity problems, but the potentially serious occurrence of mould growth as well.

To meet Building Control requirements in England and Wales, it is necessary to demonstrate compliance with Building Regulations. The latest version of the Building Regulations Part L (2013, with 2016 amendments) and associated guidance document for residential construction Approved Document L1A (ADL1A) require that thermal bridging be included in the fabric heat loss calculations. However, despite the increasingly stringent standards for thermal performance and heat losses, many designers are still not fully aware of how significantly thermal bridges can compromise the value of the installed insulation.

Thermal performance and structural integrity

Typical installation of structural thermal breaks involving concrete-to-concrete

The most effective way to minimise thermal bridging at cantilever balcony detailing is to incorporate a load-bearing structural thermal break such as the Isokorb from Schöck. This minimises the flow of thermal energy between the interior and exterior of a building, providing both structural integrity and ensuring that the balcony is thermally isolated. To work effectively over a long period thermal breaks require certain physical characteristics. Thermal insulation with an optimum thickness for the particular application, load-bearing components and a combination of reinforced steel and stainless steel. A wide variety of thermal break solutions are available from Schöck for applications as diverse as: concrete-to-concrete; concrete-to-steel; steel-to-steel; renovation projects – and even Passive House.

One consequence of thermal bridging is that surfaces can form condensation, causing visual deterioration and structural damage. However, an even bigger concern is mould growth. To identify areas where there is a risk of condensation and therefore mould growth, a ‘surface temperature factor’ (fRsi) should be used. It allows surveys under any thermal conditions and compares the temperature drop across the building fabric with the total temperature drop between the inside and outside air. Using the formula, the recommended value for offices and retail premises is equal to or greater than 0.5; and to ensure higher standards for occupants in residential buildings, equal to or greater than 0.75.

Passive House no longer a problem

Passive House uses highly energy-efficient building materials and preventing thermal bridging is essential. Until relatively recently, balconies posed a construction challenge for Passive House design. Components penetrating the insulating outer shell of a thermally highly sensitive building demanded performance standards not achieveable by thermal break products on the market at the time. However, innovative product development means that high specification ‘Passive House certified’ structural thermal breaks from Schöck are now available for many applications.

Unrivalled performance from Schöck modular connectivity solution

Building Products Index Ltd March 27, 2021 Thermal Breaks, Thermal bridging Leave a Comment

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The £2.3 billion Elephant Park regeneration project in the Elephant & Castle area of London aims to create one of the most sustainable inner-city areas in Europe. There are five phases, the third of which is currently live with eleven buildings divided into two plots – Park Central (North) and East Grove – providing 829 homes in total. Brick-finished midrise blocks to 11 and 12-storeys feature throughout and there are two main towers, one at 24-storey, the other 25-storey. Construction of the towers uses around 19,000 m²of aluminium unitised façade panels supplied by FKN and Lindner, delivered complete with integrated sliding doors and openings ready for ventilation devices. There are hundreds of cantilever steel balconies throughout the project too, also pre-fabricated (including flooring and glazed balustrades) and supplied by Dearneside Fabrications Ltd.

Avoidance of thermal bridging is critical

With steel having such high conductivity, the avoidance of thermal bridging is critical throughout. Local heat loss is a major factor, resulting in more energy being required to maintain the building’s internal temperature. Also, low internal surface temperatures local to any thermal bridge can cause condensation, which is likely to result in structural integrity problems with absorbent materials. Mould growth too is a possible risk and can cause asthma and allergies. The thermal performance at the connectivity points involving the balconies and the commercial façades therefore needed careful consideration. The Schöck Isokorb is universally recognised for its performance capability with balcony design detailing – but is less widely known for its ability to dramatically improve thermal performance involving façade engineering. On this project, as the thermal zone sits outside the slab zone, the Schöck Isokorb T type S offers the ideal solution to both situations.

Unique and versatile

The versatile Schöck Isokorb T type S structural thermal break is the ideal connectivity solution for steel-to-steel applications. There are two variants, the T type S-N for tensile force and the T type S-V for transferring compression and shear forces. It is the only approved thermal break product that satisfies the load-bearing and thermal insulation requirements for steel design. Also, being a modular unit, it can be adapted to all profile sizes and load bearing capacity requirements – plus it can be used in both new construction and renovation projects.

Totally verifiable performance

In addition to steel-to-steel, the comprehensive Isokorb range also offers solutions for concrete-to-steel, concrete-to-concrete – and even a maintenance free alternative to wrapped parapets. Products meet full compliance with the relevant UK building regulations, have NHBC approval, offer LABC Registration and the security of independent BBA Certification. The requirement that the temperature factor used to indicate condensation risk (fRSI) must be greater than, or equal to, 0.75 for residential buildings is also easily met by incorporating the Isokorb.

Contact Schöck on 01865 290 890; or visit the website at www.schoeck.com for full details of the Isokorb T type S and all other Isokorb solutions

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Schöck Isokorb for seafront Passive House Award Winner

Building Products Index Ltd September 28, 2020 Thermal Breaks Leave a Comment

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Seaton Beach Apartments in Devon is the first UK multi-residential development to be certified as passive house plus. Some claim that passive house standard is easier to achieve with simpler, box-like forms, resulting in finished buildings being aesthetically limited – but this is certainly not the case here. A little design ingenuity and the use of Schöck Isokorb thermal breaks, has enabled generous sea-facing balconies with sweeping curves to create a striking finish.

Seaton may be a traditional Devon seaside resort town, but there is nothing traditional about the eye-catching new passive house development right on the seafront. Seaton Beach Apartments is an innovative, award-winning, new development of seven luxury two-bedroom beachfront apartments, complete with a three bedroom penthouse – and is the first multi-residential development in the UK to be certified as passive house plus. Which means it is not only able to meet the ultra-low energy fabric requirement, but also generates renewable energy. The project can also boast ‘best sustainable residential development in the UK’ from the International Property Awards.

Initially though, the original architectural design was not to passive house standard. However, the developer recognised that the south-facing orientation and form factor would make it possible to reach the necessary standard. Architects Gale and Snowden, who have helped stimulate the trend for larger scale passive house projects in the region, were brought in at this point to develop the initial detailed designs and oversee the construction. The ground floor is concrete, with a monolithic clay block construction used from the first to third floors and timber frame for the penthouse. Combined with high-performance external render and internal plaster, the result is an entirely mineral hygroscopic wall build-up, which helps to regulate humidity and provide a healthy and comfortable internal environment.

Uses 90% less energy than a typical new build

Other features of the construction include low electromagnetic field wiring arrangements and a highly efficient mechanical ventilation system with heat recovery. Complete with an exhaust air heat pump for hot water supply. An array of PV panels on the roof yield an annual 14,234 kWh, resulting in the building generating more energy than it uses. There is a constant supply of silently circulated filtered fresh air within the triple glazed, airtight construction. And 90 per cent less energy used than in a typical new build. All factors which have contributed to the building achieving the stringent passive house plus target.

Passive house standard is easier to achieve with simpler, box-like forms and finished buildings are often considered aesthetically limited and rather prosaic. However, with Seaton Beach Apartments, a little design ingenuity and the use of Schöck Isokorb thermally broken balcony connectors defies this notion. The potentially unexciting building now features large sea-facing balconies with generous curves. The detailing of these balconies is critical though, if thermal bridging is to be minimised and the building’s energy performance not compromised.

The Isokorb is a technically advanced solution

Schöck Isokorb thermal breaks are installed where the balconies meet the clay block structure, as ineffectual insulation at these cantilever connectivity points will result in local heat loss. This means more energy is required to maintain the building’s internal temperature. Low internal surface temperatures around the thermal bridge can also cause condensation, leading to structural integrity problems with absorbent insulation products and the potentially serious occurrence of mould growth. The Schöck Isokorb is one of the most technically advanced countermeasures against thermal bridging. It not only thermally separates components from one another, but acts in a structural design capacity as well. The product type used here has an innovative HTE Compact compression module made of high-density micro-fibre reinforced concrete and transfers both negative moments and positive shear forces with cantilever balconies, or positive field moments combined with shear forces.

Enormous freedom of design

As the leading international supplier of structural thermal breaks, Schöck is able to offer planners complete construction dependability and almost limitless freedom of design with the options available in its Isokorb product range. There are solutions for concrete-to-concrete, concrete-to-steel, steel-to-steel, a thermally insulating connection for reinforced concrete walls – and even a maintenance free alternative to wrapped parapets. The temperature factor used to indicate condensation risk (fRSI) which must be greater than, or equal to, 0.75 for residential buildings, is easily met by incorporating the Isokorb. All products meet full compliance with the relevant UK building regulations and the NHBC. They also offer LABC Registration and have independent BBA Certification.

For a free copy of the Schöck Thermal Bridging Guide; the Schöck Specifiers Guide or to view the range of downloadable software, contact Schöck on 01865 290 890 or visit the website at www.schoeck.co.uk

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