BUILDING CONSTRUCTION
Rigid insulation solutions such as phenolic boards typically achieve lower thermal conductivities than alternatives such as mineral fibre.
for new buildings, and the values set are notably tougher than the existing or previous requirements in all three countries, with Scotland setting slightly more ambitious targets. These values are area weighted, so it
is possible to have a worse U-value in certain areas of a construction, providing that this is compensated for with better values elsewhere. In all cases the U-value of individual elements should be no worse than the threshold values shown in Table 1. It is also worth reiterating that these are just worst-case values, and that if all elements in a building are constructed to these levels, it will be extremely difficult to reach compliance.
Notional Building To calculate the targets for the first two of these metrics, assessors carry out modelling on a proposed building in the SBEM modelling software. This analysis compares the proposed development with a ‘notional building’ of the same dimensions using a set specification, the fabric elements of which are shown in Table 2.
Specifiers are free to vary from these Element type
England, Scotland, and Wales, are all updating the energy performance targets within their Building Regulations and Standards in 2022.
specifications, providing they meet the carbon emission and primary/delivered energy targets and worst-case U-values. It is worth noting that all new buildings will also need to be completed with heating systems designed to operate at temperatures of 55 °C or below. This is to allow a simpler future transition to low carbon heating technologies, such as heat pumps, which operate most efficiently at lower flow temperatures.
Thermal bridges It’s also important to be aware that changes are being introduced to how heat losses from thermal bridges are considered. Thermal bridges are areas where materials which are more conductive to heat than the insulation layer are allowed to form a path between the inside of the property and the outside. These commonly occur in areas such as around windows and doors, and at junctions between building elements. These paths can form a fast-track for heat to escape, and have been shown to account for as much as 30% of total losses. To improve practice in this area, the
Accredited/Approved Construction Details ADL2 2021 England area K)
- Pitched roof (sloping) - Pitched roof (horizontal) - Flat roof Walls Floors
Windows
(similar to residential) Other windows Rooflights
Pedestrian doors Vehicle access
and large doors
Table 1: Worst-case U-values in ADL2 2021 in England, (ADL2 2022 in Wales has not yet been published), and under TH6 2022 in Scotland.
82 Health Estate Journal October 2022
0.16 0.16 0.18 0.26 0.18
1.60 or Window Energy Rating B
1.60 2.20 1.40 1.30
TH6 2022
weighted worst-case weighted worst-case all regions U-values (W/m2
(Scotland) area U-values (W/m2 0.16
0.16 0.16 0.21 0.18 1.60
1.60 2.20 2.20 1.50
K)
0.35 0.35 0.35 0.70 0.70
Threshold U-values –
(ACDs) have been removed, as it was felt they had become outdated. The default heat loss values given where no detail is supplied (either for the junction or globally for the building) have also been worsened. This makes it much more difficult to reach compliance without either having bespoke details calculated, or making use of details from manufacturers or industry libraries.
Impact on Building Specification While we’re still waiting for the final version of the SBEM modelling software in all three regions to look at how these updates may specifically impact buildings, there are some key points to note. Firstly, the Primary and Delivered Energy metrics allow any energy generated by onsite renewables, such as photovoltaic (PV) roof panels, to be subtracted from a building’s overall demand. This means that use of these technologies is especially beneficial for compliance with this metric. Use of low carbon heating technologies, such as heat pumps, will aid compliance with the carbon emissions metric. However, as the PEF for electricity is currently higher than for natural gas, it is initially expected to be a little harder to achieve compliance with the Primary Energy metric in England and Wales. It’s also worth noting that as electricity is considerably more expensive than gas, the cost of operating these systems is expected to be higher in the near term, so if you choose to go down this route it is especially important to ensure a good level of fabric performance. Fundamentally, ensuring that the building is well insulated will aid compliance with all three metrics, and – by focusing on this area now – specifiers can minimise long-term operational costs for facilities, and ensure that buildings can be easily transitioned to full Net Zero status through more minor changes to the heating and hot water appliances. It will also help to futureproof buildings against requirements to upgrade the fabric performance of existing buildings at a later date.
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