Latest super-insulated lintels are able to achieve a Psi value of between 0.03 and 0.06. Customers that are looking to achieve the best thermal performance should choose a lintel with the lowest Psi value. Our PSI value calculator, which is accessible via PC, tablet or mobile, can be found at www.birtleylintels.co.uk/psi-calculator/. Users simply input cavity width, block and insulation details, along with lintel length, for the tool to provide the required PSI value in W/mK. PSI values, which are a measure of non-repeat thermal bridging, are an essential piece of data for anyone looking for cost effective ways of assessing or maximising the energy efficiency of the building by reducing thermal or ‘cold’ bridging. These PSI tools are proving to be invaluable to specifiers and designers because it provides them with accurate heat transmittance data on nonrepeating thermal bridges at design stage. Supplying this data to the energy assessor will also ensure that the SAP calculation accurately represents the lintel specified at design stage. lintel can therefore cut heat loss through thermal bridging by more than 75% and make significant improvements in SAP calculations. In terms of actual performance, a thermally broken lintel can improve both the dwellings CO2 emission rate (DER) and fabric energy efficiency rate (DFEE) by 3% and 1% respectively. In the case of a small detached dwelling of around 105m² the reduction in heat loss from a thermally broken lintel is equivalent to upgrading from a double to a triple glazed window. These savings are greater on a larger dwelling of 304m2, where the impact of upgrading to a super-insulated lintel can mean the cavity wall thickness is reduced from 150 to 125mm. This is another significant saving for your client in terms of insulation and masonry ancillaries. It also avoids the loss of internal living space as wider cavities have a tendency to encroach on the internal footprint. Unconstrained by composite materials which need a linear cross section to make them economical, these latest generation thermally-broken lintels have as much flexibility in design as any purpose made lintel, and each leaf can be tailored to suit any wall construction. Summary As incremental improvements in energy efficiency become ever more expensive, simple steps such as specifying a thermally broken lintel can make a huge difference to overall thermal performance and cost of the dwelling. As a result more specifiers and contractors are referring to the Psi value before choosing a lintel, and that is one of the reasons why we make them freely available on our website. Accredited energy assessors are also able to use this Psi data with their thermal modelling software to calculate accurate heat losses at junctions. Having a joined up approach with all parties using thermally broken lintels and referring to relevant Psi values ensures that an accurate calculation of the dwellings energy efficiency is the end result. The simple fact is that thermally broken lintels provide architects, housebuilders and structural engineers access to a truly customisable solution when looking for ways to achieve significant reductions in building fabric heat loss. www.birtleylintels.co.uk DOORS, WINDOWS, GLAZING AND ACCESSORIES Lintel life expectancy The lower the Psi value, the better the thermal performance MARCH 2018 | BUILDING PRODUCTS 27 Psi value calculator When choosing a steel lintel, it is important to make sure that it has undergone hot-dip galvanizing post fabrication. This is where the material is galvanised after it is cut, bent and processed into the finished lintel, which ensures all surfaces receive the same consistent coating. A lintel that has undergone hot dip galvanising post fabrication to EN1461 can have a life expectancy of up to 170 years. It also results in 50% more zinc protection than other approved coatings. Conversely, when the steel is galvanised before it is made into the lintel the result is that the galvanising can be compromised, for instance at cuts and bends, and these are often finished with paint. Unfortunately paint is easily damaged and this can result in result in corrosion of the steel.
Building Products March 2018
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