February 2022

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Knauf Technical Talk U-VALUE CALCULATIONS EXPLAINED Approved Document L (Part L) of the Building Regulations sets out how energy efficient buildings and individual building elements must be. But how do you know whether the build-up meets the required minimum standards? This month, Bradley Hirst, Technical Services Manager at Knauf Insulation, looks at U-value calculations in more detail. What are U-value calculations? U-value calculations measure whether the proposed build-up will meet the minimum standards by determining how well it will prevent heat transfer. They are measured in W/m²K (watts per metre squared Kelvin) and the lower the U-value, the more effective the build-up is. This means less energy will be needed to heat or cool a space, so a property with high levels of insulation is more energy efficient. Knauf Insulation says numerical calculations (3D U-values) are highly accurate, so they should be used for rainscreen façade systems rather than the simplified method. Do I need a U-value calculation for every project? Not necessarily. Every project must meet the limiting standards for fabric energy efficiency, so architects usually include a specification in their plans. For insulation, they may list a product name or the thermal resistance (R-value) which has been verified to achieve compliance. If you follow the specification exactly, you won’t need to undertake additional U-value calculations. “If you change any element, you will need new U-value calculations to demonstrate compliance” But you may need to change the specification. For example, on a rainscreen façade system build-up, you may decide to improve the building’s fire safety strategy by swapping combustible insulation for a non-combustible solution such as Knauf Insulation’s Rocksilk RainScreen Slab. If you change any element, you will need new U-value Left: Bradley Hirst, technical Services Manager at Knauf Insulation. Below: Knauf Insulation Rocksilk(R) RainScreen Slab is non-combustible making it suitable for use on buildings of any height. calculations to demonstrate compliance. For applications such as cavity walls or flat roofs on extensions, many installers draw on experience and use the same build-up for every project. This may save time but remember Part L changes in June 2022, so check with your insulation manufacturer’s Technical Team that your chosen build-up meets the new minimum standards. Are all U-value calculations the same? How U-values are calculated is set out by BRE’s BR443 (Conventions for U-value calculations). There are two common methods: simplified calculations and numerical calculations (3D U- values). Which method is used depends on the application and the accuracy required. Simplified calculations are best for straightforward build-ups with few variables such as brick and block walls. But they aren’t recommended for rainscreen façade systems because the blanket correction factor doesn’t accurately represent the system’s thermal performance. Instead, contractors and installers should insist on 3D U-value calculations which consider the complex interaction between the insulation, façade, and rail and bracket system. This high degree of accuracy often identifies solutions that would have been ruled out by the simplified method and ensures the thermal performance of the final building matches its design. Contact Knauf Insulation www.knaufinsulation.co.uk @KnaufUK 56 TC FEBRUARY 2022
ROOF TUBE maximise the exposure and make video content more accessible www.roof-tube.co.uk - Build your own channel and create a new audience for your content - We can compile playlists ensuring relevant content is shown to your target audience and Safety Equipment put your business and products in front of a new audience (QUITE INTERESTING) INSULATION FA ACTS By QI (Quantum Insulation Ltd) Non-combustible inverted roof insulation update Since September 2019, we have produced 22 of these monthly QI@QI information articles, with three pieces covering the increasing demand for noncombustible insulation boards. So, where are we as we enter 2022 and await the outcome of the consultation on regulation 7 of Approved Document B. In reality very little changed in the non-combustible insulation board market in 2021, other than FO AMGLAS® INVATHERM TM being accepted by the NHBC, as long as the below criteria are met.As the only non-combustible inverted roof insulation board in the UK market, this is an important step, NHBC requirements for FOAMGLAS® INVATHERM TM : • covered by a Water Flow Reducing Layer (WFRL) ‘A1’ or A2’ • that the pedestals have a circular base with a diameter of at least 170mm and be supported by a rubber underlayment. • the maximum load indicated in the Product Data sheets is not exceeded. In the world of warm roofs FOAMGLAS® and ROCKWOOL® continue to be the only sources of non-combustible roof insulation board, with the penalty of a greater thickness for a given U-value versus PIR insulation, plus a greater One ‘grey area’ that was partly cleared up in 2021 was the requirements for non-combustible insulation on the upstands of a roof on a ‘relevant with the Ministry of Housing Communities & Local Government (MHCLG) - now the Department for Levelling Up, Housing & Communities (DLUHC). Acceptance by the regulators in the other three nations needs to be The upstand rules for England are that non-combustible insulation board is required if: surface. • the upstand insulation is thicker than 60mm. • the upstand insulation spans across a compartment wall line. • the upstand is against habitable space. Copies of this guidance can be downloaded at: LRWA-SPRA-Guidance-Note-Changes-in-Fire-Safety-Regs-0621-FINAL.pdf * a ‘relevant building’ is one where there is a storey at least 18m abov ve ground level that contains dwellings or institutions or a room for residential purposes (excluding any room in a hostel, hotel or a boarding house), student accommodation, care homes, sheltered housing, hospitals and school dormitories in buildings. Next month: For more information contact andydunn@media-now.co.uk or jakeroxborough@media-now.co.uk FEBRUARY 2022 TC 57
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February 2022

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