TECHNICAL FOCUS
INCORRECT U-VALUE CALCULATIONS JEOPARDISE OUR FUTURE Incorrect U-value calculation is a big problem for the industry. To provide insight as to what can be done, James Wilkinson, Design Team Manager at flat and tapered roof insulation specialist Gradient, argues why accurate and compliant U-value calculations matter, highlighting to specifiers the need to ensure they have not been mis-sold and are providing their clients with the thermal performance they require.
U
-values are vital. Not only do they determine the anticipated thermal efficiency of a building’s fabric, they are a must for new-build and refurbishment projects. U-values reveal whether a property has met regulation energy standards. But why are the calculations executed so carelessly? Calculations should and must be done in strict accordance and conformance to standards and regulations. Frustratingly, at present, the calculations are frequently carried out with little regard of the importance of compliance. This disregard is deeply worrying, placing homeowners
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at risk and causing the increase of CO2 emissions – quite the opposite of what is intended.
Meeting U-value requirements U-values measure the transfer of heat through a structure. They feed into a building’s overall performance alongside Psi-values and renewable technologies, such as heat pumps and solar panels. The lower a U-value is, the more thermally efficient the buildup is – meaning the more cost effective homes are to heat. There are, however, high levels of inaccuracy that exist in U-values used in Building
Regulations submissions. This hefty issue is having a negative impact on compliance and the energy efficiency of the building, putting homeowners in difficult positions and increasing CO2 emissions. When it comes to achieving required U-values for domestic new-build projects, it’s a requirement to discuss the stipulated outcome with an energy consultant who can give advice based on the Standard Assessment Procedure (SAP). With this methodology, the thermal ratings of walls, floors, roofs, junction details and any renewable technologies are put into a metaphorical mix,
the performance of which will hopefully correspond with, or exceed, the required regulations for the building. These elements can be changed, as long as the property achieves the required dwelling performance. The alternative to carrying out the SAP assessment is to work on the notional dwelling specification, which has to be followed as a minimum to achieve a pass. Working to backstop values only, however, will result in failure. The SAP assessment is quite complex, as it allows for a compensatory approach to the elements involved. For example, if a designer is struggling to hit a U-value target due to height issues with a roof, the performance deficit can be made up by installing additional insulation in areas such as walls and floors. With new builds, therefore, adjustments to U-value outcomes can tip the balance in favour of achieving the required performance targets. For commercial properties, Simplified Building Energy Modelling (SBEM) is the approved national calculation methodology used to highlight
