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Building Products March 2018

DOORS, WINDOWS, GLAZING AND ACCESSORIES SUPPORTING ENERGY EFFICIENCY Lintels are an important but often overlooked part of reducing thermal or ‘cold’ bridging. Here, Zoe Watson, group marketing manager at Birtley Group, looks at the reasons why a correctly specified lintel can be equivalent to upgrading from double to triple glazing, at a fraction of the cost. Lintels are an essential structural element in most buildings, yet they are often overlooked for the improvements they can make in overall energy efficiency. For instance, with ever more stringent thermal performance requirements, choosing the correct lintel can reduce heat loss through thermal bridging by around 75% when compared to a standard cavity wall lintel. The primary purpose of a lintel, of course, is a structural beam that carries the weight of the wall above an aperture such as a window or door. The most common type of lintel is made from galvanised steel because it is lighter than concrete and so is easier to handle on-site, while being extremely rigid. Standard lintels are made from a single piece of highly conductive steel that interrupts the line of insulation and it is this that results in thermal 26 BUILDING PRODUCTS | MARCH 2018 bridging. With around eight to 10 windows and two door apertures per property, this thermal bridging can account for around a third of the total heat loss from a dwelling. As such, taking steps to minimise thermal bridging along the lintel can be a very costeffective, reliable and robust method of achieving compliance with building regulations. Thermally-broken lintels Recent changes to Building Regulations mean that a building’s fabric performance must now hit a Target for Fabric Energy Efficiency (TFEE) in addition to the traditional Target Emission Rate (TER) for CO2. This means that more emphasis is put on reducing heat loss, a significant proportion of which can be attributed to lintels and other non-repeating thermal bridges. The thermal bridging performance of a lintel is expressed in terms of its Psi value. Latest generation lintels are able to achieve a Psi value of between 0.03 and 0.06. The lower the Psi value, the better the thermal performance. Energy assessors, when working on a building constructed to Part L Accredited Construction Detail, tend to use an approved value of 0.3W/mK for lintels without a baseplate. In reality, a heat loss of 0.3W/mK makes the assumption that the line of insulation is interrupted with a highly conductive, traditional steel lintel. However, this does not reflect actual heat loss from latest generation, thermally-broken lintels. For example, even with our 1,500mm standard lintel the Psi value is 0.18 W/mK, although upgrading to our Supatherm lintel at the same length improves thermal performance to 0.043 W/mK. Replacing a traditional lintel made from a single piece of metal with a thermally-broken


Building Products March 2018
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