As part of the updates to Part L to the Building Regulations in England and Wales and Section 6 (Energy) of the Building Standards in Scotland, which come into force in 2022, there is set to be a much greater focus on addressing thermal bridging in properties. The standard Accredited/Approved Construction Details are set to be removed and the default values used when details aren’t supplied will be worsened, making it much more difficult and costly to reach compliance without accurate details.
When considering linear or geometric thermal bridges, designers therefore have a choice to either use pre-calculated details from a suitable database, obtain product specific calculations from a manufacturer, or, where these aren’t available, to create their own details and Psi-value calculations. These will need to be produced by a suitably qualified individual following the guidance in Building Research Establishment’s BR 497, and the temperature factors set out in Building Research Establishment’s Information Paper 1/06.
Whilst this presents some additional challenges, use of pre-calculated product details or bespoke details can also provide clear benefits both for property performance and for maintaining specifications through to the final build.
Learn more about the changes to the building regulations in relation to detailing.
How bespoke details can benefit property performance
The most obvious benefit of using a pre-calculated detail from a manufacturer, or calculating your own, is that you can often achieve far lower Psi-values (calculated heat loss) for these junctions. This can make it both simpler, and potentially cheaper, to achieve compliance with the requirements of the updated Part L and Section 6 within SAP and SBEM, as more costly elements such as renewable technologies may no longer be needed or may be downsized.
This is especially important given that the 2021 versions of Part L in England and Wales are essentially seen as a stepping-stone to much more stringent energy performance standards due in 2025. By this point, the carbon emissions from new homes are expected to be between 75-80% lower than at present. By looking to address thermal bridging now, rather than relying on renewables to achieve compliance, project teams can get ahead of the curve.
In addition to supporting compliance on paper, bespoke details should also help to ensure the heat losses at these junctions are accurate when compared with the as-built junction – helping to close the performance gap. This is supported by new requirements within the updated versions of Part L and Section 6 for contractors to complete a compliance report supplemented with pictures of all key junctions before they’re covered up.
This more thorough approach to design and installation should provide greater certainty that junctions perform as expected, not only limiting heat loss, but also preventing further issues related to thermal bridges, such as the formation of condensation which can damage a property and lead to potential health issues including mould growth.
To support contractors, designers must also think carefully about how practical the designed junction will be to sequence and install when on site.
Read some tips on how to create workable details.
Correct detailing is also fundamental to the fabric first approach to construction, working in combination with improved U-values for the constructions to ensure the building retains heat more effectively. This will be especially important as we transition to low carbon heating technologies, such as air source heat pumps, which perform most efficiently when operating at lower flow temperatures.
Learn more about the benefits of a fabric first approach to compliance.
How bespoke details can strengthen specification
Along with improving the overall energy performance of a property, bespoke or pre-calculated product details can also help to ensure the original specification is carried through to the final build. This is because factors such as the insulation product’s thermal conductivity and emissivity will be incorporated into the Psi-value calculation. As a result, the value is non-transferable to a different material – helping to prevent last-minute changes.
This will again be supported by the requirement for project teams to document the actual measures installed on a property. This represents an important step in developing and protecting the Golden Thread of information about the construction of a property, supporting its long-term maintenance.