Section 6 Energy 2021 – New Homes

29 November 2021 Kingspan Insulation UK
Kingspan-section-6-energy-2021 existing-homes-en-gb-01

At the end of July, Scotland joined England and Wales in launching a consultation looking at updating its energy performance targets for all new and existing buildings. In Scotland, these are contained within Section 6 (Energy) to the Building Standards. The changes are due to come into force in 2022 and will lay the path towards a new low carbon heating standard expected in 2024, which will require virtually all new buildings to be heated through low carbon technologies.

New carbon emissions targets

The Scottish consultation for new homes asks responders to choose between a 32% or 57% reduction over current carbon emissions targets.

Unlike the English and Welsh documents, the Scottish consultation doesn’t select a preferred option, so it will be interesting to see what feedback they receive. In Wales, around half of responders backed the lower (37% reduction) target whilst 30% were in favour of the more ambitious target (56% reduction). The current Scottish standards are already tighter than their equivalents in England and Wales, so the proposals are truly a significant, but achievable, step towards net zero buildings (and not that dissimilar to Passivhaus levels of performance).

Primary Energy or Delivered Energy

As with the English and Welsh consultations, the Scottish document considers the introduction of Primary Energy as the new principal metric, with carbon emissions retained as a secondary metric. Primary Energy looks to estimate the total energy used by a property, including all of the energy needed for steps such as extracting, refining and transporting the fuel.

Learn more about Primary Energy

The consultation notes, however, that the use of this metric may cause some issues for the transition to low carbon heating. Whilst the updated carbon emissions factors for electricity are much lower than for gas (due to grid decarbonisation) it still has a higher Primary Energy Factor in SAP 10.2 (1.501 for grid electricity vs 1.130 for gas). As a result, it may be simpler to reach compliance with the Primary Energy metric for properties with a conventional gas boiler (although additional requirements have been added where gas is used instead of a heat pump).

As an alternative, the consultation asks if the industry would prefer to use a Direct Energy metric instead. This would solely look at the total energy supplied to a property (minus any offsetting for renewables) and would ignore energy used in upstream activities. As such, whilst this may help to prevent homes with heat pumps being penalised, it may come at the cost of a deeper understanding of the energy demand of buildings.

Limiting benefits from on-site generation

The consultation also notes that analysis of Energy Performance Certificate (EPC) data from homes built to the current (2015) standard which often showed only marginal improvements in fabric performance over homes built to the previous standard. Instead, project teams chose to install renewable generation such as photovoltaic (PV) panels. 

To encourage developers to adopt a fabric first approach for homes built to the new standard, the consultation proposes more detailed assessments of onsite renewable generation to ensure that only the generated energy that is used by the building is considered in the Primary Energy and carbon emissions calculations. Any energy which is exported to the grid will not be considered for these metrics. 

Tighter maximum U-values

To further support a fabric led approach, the consultation also sets stricter maximum U-value targets for both emissions options. In fact, the values proposed for Option 2 would actually be tougher than those proposed for the Notional Dwelling in the Part L 2021 consultations in England and Wales. At the same time, Scotland will continue to allow localised areas of the fabric to be relaxed, provided this is compensated for elsewhere in the envelope. The absolute limits for individual elements' U-values are set at 0.70 W/m2K for walls and floors and 0.35 W/m2K for roofs. 

Element type Current (2015) new build limiting U-values Option 1- Improved maximum U-value Option 2- Advanced maximum U-value
All roof types (W/m2K) 0.15 0.12 0.11
Walls (W/m2K) 0.22 0.17 0.16
Floors (W/m2K) 0.18 0.15 0.13
Party Walls (W/m2K) 0.20 0.00 0.00
Windows and doors (W/m2K) 1.60 1.40 1.20


Two notional buildings

The consultation also proposes streamlining the multiple notional dwellings in the existing version, which include simplifying approach packages for LPG, Oil and Biomass, to just two fuel types. The first new notional package uses an air source heat pump and can be used when designing a property using either air or ground source heat pumps, whilst the other package features a gas boiler and will set the compliance targets for all other fuel types, requiring any poorer performing fuel to do more to compensate.

Consideration was given to providing only one notional dwelling, however this proved difficult, as if the notional dwelling used a gas boiler, then properties with a heat pump could reach compliance with a much laxer specification in other areas. Conversely, one set based on the use of a heat pump would be extremely difficult to meet for other fuel types.

The two notional dwelling options show notably improved fabric performance over the existing requirements. Interestingly, Option 2 also incorporates the use of a mechanical ventilation with heat recovery (MVHR) unit and much lower air-leakage rates – reflecting a more Passivhaus type approach. Dwellings using a heating type represented by the gas boiler also require the use of wastewater heat recovery (WWHR) and photovoltaic panels (PV) for setting compliance targets.

Developers remain free to deviate from the notional dwelling providing they meet the Primary Energy, carbon emissions and maximum U-value metrics.

Element Type Current (2015) notional building (gas) Current (2015) notional building (ellectric)  Option 1- improved notional building Option 2- advanced notional building
All roof types (W/m2K) 0.11 0.11 0.09 0.09
Walls (W/m2K) 0.17 0.17 0.15 0.13
Floors (W/m2K) 0.15 0.15 0.12 0.10
Party walls (W/m2K) 0.00 0.00 0.00 0.00
Windows (W/m2K) 1.40 1.40 1.20 0.80
Doors (W/m2K) 1.40 1.40 1.20 1.00
Air Permeability (m3/m2/Hr@50Pa) 7.00 7.00 5.00 3.00
Ventilation Natural with extract fans Natural with extract fans Natural with extract fans MVHR
Heating emitters Regular radiators Regular radiators Design flow temperature = 55oc Design flow temperature = 55oc
Heat appliance  89.5% gas boiler 175.10% electric (heat pump) Air source heat pumps 250% 89.5% gas boiler Air source heat pumps 250% 89.5% gas boiler
WWHR Yes Yes No Yes No Yes
Photovoltaics Yes (0.01m2 x TFA) No No 40% ground area No 40% ground area

ACDs removed

In line with the changes in England and Wales, Scotland also expects to withdraw its own Approved Construction Details (ACDs) when the new version of Section 6 is published. These are pre-created details that designers can use when looking to address thermal bridges at junctions. They will, however, retain the introductory advisory guidance.

Additionally, the default PSI-values for junctions and global Y-value will be worsened in SAP 10.2. This means it will be more difficult to achieve compliance unless you are using calculated values for key junctions. This change forms part of efforts to close the performance gap between the expected and actual energy performance of buildings as thermal bridges have become an increasingly key source of heat losses as the fabric insulation performance has improved.

Learn more about the change to detailing in Section 6

Preparing for Heat Pumps

As part of the expected transition to low carbon heating, the heating system in all new homes will need to operate at a flow rate temperature of 55 °C. This supports heat pumps which operate more effectively at this temperature. Additionally, where a building is fitted with a gas boiler or other ‘non-zero direct emissions technology’, the developer will also be required to detail the process for how this can be retrofitted with a zero carbon alternative with minimal disruption. 

The tighter building fabric backstops provided in the new guidance should also help to reduce the likelihood of direct electric heating being needed to ‘top-up’ supply during periods of high demand when a heat pump is installed.


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