Net Zero Carbon Supplementary Planning Document
4. Policy NZC2(A) – Making Buildings Energy Efficient
Policy NZC2(A): Making buildings energy efficient
New development of one or more new dwellings (C3 or C4 use) are expected to demonstrate a 10% improvement on the Part L 2021 Target for Fabric Energy Efficiency.
New developments of 1,000sqm or more of new non-residential floorspace, hotels, (C1 use class) or residential institutions (C2 use class) are expected to demonstrate that they achieve a 19% reduction in carbon emissions compared to Part L 2013 through energy efficiency measures (fabric efficiency, efficient services and efficient energy supply; steps 1 and 2 of the energy hierarchy).
Where full compliance is not feasible or viable having regard to the type of development involved and its design, proposals must demonstrate through the energy statement that carbon reductions to the greatest extent feasible through energy efficiency measures have been considered and incorporated.
All energy statements must also lay out the U-values and airtightness of the proposed building in comparison to the notional values in the Future Homes Standard or Future Building Standard (indicative specification, or final, as available at time of application).
4.1 Policy NZC2(A) represents the first step in the energy hierarchy: energy efficiency. This refers to the design of buildings to minimise the demand for energy, regardless of the source of that energy.
4.2 This is a vital step towards the DPD's expressed objective to ensure new buildings are planned and constructed to be net zero regulated carbon in operation. High fabric efficiency in new buildings ensures that new buildings do not add to the significant number of existing buildings in the District that will need costly and disruptive retrofit in order to play their necessary role in meeting the locally committed or nationally legislated net zero carbon transition. It has been shown that to retrofit a home to a net zero carbon performance standard costs three to five times more than it does to build to that standard in a new build15.
4.3 The energy efficiency targets set by Policy NZC2(A) for new buildings is summarised in Table 3.
4.4 The key ways in which energy demand can be minimised are:
- Orientation and solar gain: Designing the building's layout and glazing so that the building gains the optimal benefit of light and heat from the sun, to minimise the need for artificial heat and lighting while avoiding the risk of overheating from sunlight. See Figure 3 for an illustration.
- Building form: Having a more compact, simple building shape rather than an extensive, complicated building shape reduces the ratio of external surface compared to the area of internal space, and reduces the number of joins between different parts of the wall or roof. Together, this reduces the points where heat is likely to be lost to the outside. See also Figure 4 illustration of what different residential form factors could look like.
- Fabric: Improving the insulation value of walls, windows, floors and roofs, improving the air-tightness of the whole building, and reducing 'thermal bridges' (points where a more heat-conductive element of the building forms a bridge from inside to outside allowing heat to be lost).
- Efficient energy supply: Using types and sources of energy that minimise losses in the generation and distribution process, and/or which use waste heat (see Section 5).
- Efficient services and appliances: Ensuring that the heating system, ventilation, lighting, appliances and other energy-using devices installed within the home are able to deliver the maximum function for the minimum amount of energy input.
Table 3: Summary of Policy NZC2(A) requirements by building type, and rationale.
|
Use type |
Baseline measure |
Baseline edition of Building Regs |
Required improvement on baseline |
|
New development of one or more dwellings (C3 or C4 use class) |
Part L Target Fabric Energy Efficiency (TFEE) |
Part L 2021 |
-10% |
|
New development of 1,000sqm or more of new non-residential floorspace, hotels (C1 use class) or residential institutions (C2 use class). |
Part L Target Emission Rate |
Part L 2013 |
-19% |
|
Where it is not feasible to meet the applicable target noted above, proposals must demonstrate that carbon reductions to the greatest extent feasible have been pursued. This should be identified in the Energy Statement. |
|||
Chart showing how a well-insulated building’s
space heat demand increases as the main
window turns further away from the south.
Please note: The yellow bar denotes heat
demand, not sun coverage, as the north-facing
window has no direct sun. Credit: LETI.
Please also note that the higher solar gain from southfacing windows is also a risk factor for overheating in highly insulated and airtight buildings; therefore it is important to ensure that designs are balanced so as to maximise the benefit reduced heating demand while also avoiding triggering the need for active cooling, whose energy consumption could negate the energy savings of the reduced heat demand. Overhead shading of south- and west-facing glazing, using deep insets or brise-soleil, can help avoid this problem by blocking summer sun (which comes at a high angle) while still allowing the building to receive winter sun (which comes at a low angle).
4.5 All of the above measures are encouraged and applicants should provide narrative on these within the Energy Statement and a general indication of the energy efficiency benefits they impart to the design.
4.6 To comply with Policy NZC(A) and demonstrate an improvement on the Part L baseline, improved fabric, efficient energy supply, and efficient hot water, fixed lighting, heating and cooling services will be required (please see the full Part L document and SAP for full list of regulated services within Part L).
4.7 Please note: the addition of renewable energy technologies (like solar panels, etc) does not count towards 'energy efficiency' requirement in most cases. Instead, these would contribute towards ‘energy efficiency’ requirement in most cases. Instead, these would contribute towards the separate requirements of Policy NZC2(B) Zero or Low Carbon Energy Sources and Zero Carbon Ready Technology. However, in non-domestic development only, there is some overlap between
an ‘energy efficiency’ measure and a ‘low carbon energy supply’ measure. This overlap and how to handle it is detailed under ‘meeting the requirements in proposals of 1,000 sqm or more of non-domestic development’, below on page 27.
Diagram illustrating what different form factor numbers look like in practice, and their relative impact on space heat demand. Credit: NHBC, 2016.
Meeting the requirements in proposals for 1 or more new dwellings
4.8 Policy NZC2(A)'s new dwelling requirement for a 10% improvement on the Part L 2021 TFEE (Target Fabric Energy Efficiency) is based on the expected fabric specification for the Future Homes Standard (Part L 2025). Thus it is anticipated that most new dwellings follow the FHS notional building fabric specification. This FHS notional building specification is replicated below as it was laid out in the Government's FHS Consultation Response.
4.9 The 'U-value' of each element represents how heat-transmissive that element is. A lower U-value means less energy loss and greater energy efficiency.
4.10 A lower 'air permeability' number means less energy loss via air moving in and out of the building. Thus, a lower 'air permeability' score represents greater energy efficiency.
Table 4: Dwelling fabric specification baseline and recommended improvement.
|
Building fabric element |
Part L 2021 notional dwelling16 (BASELINE) |
Future Homes Standard Part L 2025 notional dwelling17 (RECOMMENDED TO MEET POLICY NZC2(A)) |
|
External walls (including semi-exposed walls) |
U value 0.18 W/(m2.K) |
U value 0.15 W/(m2.K) |
|
Floors |
U value 0.13 W/(m2.K) |
U value 0.11 W/(m2.K) |
|
Roofs |
U value 0.11 W/(m2.K) |
U value 0.11 W/(m2.K) [no change] |
|
Doors* |
U value 1.0 W/(m2.K) |
U value 1.0 W/(m2.K) [no change] |
|
Windows and glazed doors |
U value 1.2 W/(m2.K) |
U value 0.8 W/(m2.K) |
|
Roof windows** |
U value 1.2 W/(m2.K) |
[Not separately specified in the FHS consultation response; presume same as other windows as above, i.e. 0.8 W/(m2.K) if vertical] |
|
Rooflights*** |
U value 1.7 W/(m2.K) |
[Not separately specified in the FHS consultation response] |
|
Air permeability (airtightness) |
5 m³/(h·m²) at 50 |
5 m³/(h·m²) at 50 Pa [no change] |
Please note: For all elements shown here, a lower number means a lower amount of energy lost via this element. Therefore, lower numbers equal greater energy efficiency.
4.11 Applicants are required to lay out their proposed building fabric specification alongside that of Part L 2021 and FHS 2025, in their Energy Statement and Energy Pro Forma.
4.12 Applicants are not required to build precisely to the Future Homes specification described above; considering that a lower performance in one building element (e.g., windows) may be able to be balanced out by better-than-notional performance in another (e.g. airtightness).
4.13 If the applicant has applied all of the above measures and these do not deliver the required 10% improvement on the TFEE, the applicant is recommended to pursue air tightness improvements as there is no pre-existing improvement in in air tightness between the 2021 and 2025 fabric spec and airtightness can contribute a great deal to energy saving. Please note that a greater airtightness may, beyond a certain level, trigger a need for mechanical ventilation and heat recovery (MVHR).
4.14 Please note: TFEE includes any demand for active cooling as well as heating. Therefore it is important to ensure that dwelling designs are carefully balanced so as to avoid the need for active cooling as far as possible, by ensuring that the building is not subject to excessive heat gains (for example, designs should carefully optimise the amount of solar heat gain from sunlight entering via glazing, so that the optimal winter gains are achieved to reduce heating demand while avoiding excessive gains in summer). Where it is unavoidable to use some active cooling, it is recommended to provide this with heat recovery for hot water uses, and to provide any active cooling through a reversible heat pump system (as the home is likely to need a heat pump anyway, to meet the overarching carbon reduction required by Policy NZC1).
Meeting the requirements in proposals of 1000sqm or more of non-domestic development
4.15 The requirement for non-domestic buildings is a 19% improvement on the Part L 2013 Target carbon Emission Rate (TER) delivered by energy efficiency measures.
4.16 The selected Part L 2013 baseline should reflect the same type of building as the proposal.
4.17 For the purposes of this policy, ‘energy efficiency measures’ in non-domestic proposals shall be defined as:
- Fabric efficiency measures, i.e., improvements to insulating value of external building element insulating properties (U-values) and air-tightness.
- Efficient regulated energy-using fittings and services, such as cooling, ventilation, lighting, fans and pumps.
- Waste heat recycling systems such as wastewater heat recycling or heat sharing loops that capture heat rejected to active cooling systems and reuse this in other forms.
- Selection of proposed heat system with a greater efficiency than that specified for that respective heating type in the Part L notional building specification.
- Other efficient energy supply and distribution systems that are not proposed to be counted under the separate required contribution from ‘renewable energy’ measures (see guidance for Policy NZC2(B)).
4.18 In the case of non-domestic development, some guidance may be needed regarding whether certain heat system measures should be classed as ‘energy efficiency’ measures or ‘renewable and low carbon energy’ measures. It is recognised that some heat delivery technologies can include elements of both efficiency and low carbon/renewable energy supply. To allow flexibility, this SPD will allow that any of the following hybrid ‘efficiency/energy supply’ measures in non-domestic development may be classed as ‘efficiency measures’ contributing towards the initial 19% TER improvement:
- Heat pumps: These provide an excellent ‘efficiency’ to the user in terms of the amount of metered electricity they draw from the grid, as they deliver approximate three kWh of heat for every kWh of electricity they use (although this is achieved because the heat they deliver is partially ‘renewable’ in that it is borrowed from outdoor ambient heat in the air, water or ground, this shows up as an ‘efficiency’ saving to the user).
- Heat networks that, by economies of scale, have an improved ratio of fuel input to heat delivered in the home, compared to a gas boiler. However, in general, gas-fired Combined Heat and Power (CHP) should still be avoided as this is still a fossil fuel use even if sometimes more efficient than individual gas boilers – for more detail, see guidance relating to Policy NZC2(B). Heat network (or ‘district heat’) CO2 factors per kWh are laid out in the National Calculation Methodology Guidance (see 2013 or 2021 version as applicable to your baseline); improvements on these notional factors can be counted as energy efficiency measures contributing to Policy NZC2(A).
4.19 Please note that this flexibility in classification of these heating measures as energy efficiency measures applies only to non- domestic development. If your scheme includes any dwellings, those dwellings should still meet the required 10% improvement in building Fabric Energy Efficiency regardless of whether your scheme also uses some of the 'energy efficient supply' measures above.
4.20 If your proposal is a mixed-use scheme that includes dwellings and non-domestic buildings which share any parts of their energy system – for example a heat network – the above measures would count towards the overarching requirements set by Policy NZC1 for minimum total regulated carbon emissions reduction in each respective use type.
4.21 In general, it should be feasible to achieve the required 19% improvement on 2013 TER primarily through a combination of fabric measures, other building services efficiencies, and use of modern heat systems with greater efficiencies. Much commercial development is likely to pursue a heat pump system, especially as reversible heat pumps can also meet the need for summer cooling. Modest improvements to fabric and services would further assist, especially in cases where it is not feasible or viable to use a heat pump system.
4.22 In fulfilling the energy efficiency improvements requirement of Policy NZC2(A) in non-domestic developments, applicants are required in their Energy Proforma to lay out their proposed building specification for all elements that are proposed as ‘energy efficiency measures’, alongside the respective equivalent elements of the notional building of Part L 2013, 2021, and 2025 (where available); see Annex.
4.23 Justification should also be provided in the Energy Statement on the reasons for the selected measures in respect to their suitability and effectiveness for the type of development proposed and (where relevant) the site characteristics.
4.24 Overleaf (Table 5) provides general guidance on the range of energy efficiency measures that are likely to be suitable and effective in key prevalent types of non-domestic development.
Table 5: Recommended energy efficiency measures in non-domestic development
|
Measure |
Contributes to Part L TER improvement? |
Description and rationale |
|
Orientation |
No, (but see 'glazing ratio' below) – but commentary on this topic is strongly encouraged and will be considered in assessing your energy statement |
Non-domestic buildings tend to have a higher occupancy of people and electrical equipment. This can bring a higher risk of overheating which can be worsened by excessive solar gain in summer. This is especially the case where the glazing is south-facing, east- or west-facing. To avoid this problem, you could:
The design process should explore what is the optimal level of solar gain for your building's anticipated occupancy so that there is a balance between minimising the need for mains heating in winter while avoiding overheating in summer so as to avoid or minimise the need for active cooling, which consumes energy. See also 'glazing ratio and G-value'. |
|
Improve glazing ratio and G- value |
Yes Indirectly, by avoiding the need for active cooling systems (if reducing solar gain) or heating (if increasing solar gain) |
These measures can help address the risk of overheating due to solar gain (the importance of which in non-residential is described above). • Changing the ratio of glazing from the notional glazing ratio set by SBEM: The SBEM notional 'reference building' has a set amount of glazed windows ('opening areas') as a percentage of walls and roofs. Increasing or decreasing glazing will respectively increase or decrease the amount of solar gain, thus either reducing the need for heating systems (if the glazing is also sufficiently insulated) or reducing the need for active cooling systems. The appropriate ratio will depend on the building's occupancy, uses and orientation. • Reduce the G-value of the glazing(amount of sunlight energy that is transmitted through the glass): This can help to mitigate overheating and thus reduce the need for cooling. |
|
Building form factor |
No, because of how Part L works – but commentary on this topic is encouraged and will be considered in assessing your energy statement |
Simpler building shapes lose less of their space heating to surface area and draughts. Recommended form factors for non-domestic are here noted, replicated from LETI Climate Emergency Design Guide:
|
|
Fabric: U value improvements and air- tightness. |
Yes |
Reduces the amount of heating energy needed by:
An improvement on the notional building U-values laid out in the National Calculation Methodology (NCM) Modelling Guide18 would help to deliver the required improvement. As the current NCM Modelling Guide is for the 2021 Building Regulations, the values laid out in that NCM Guide are already an improvement on the Part L 2013 regulations against which the DPD policy requirement is set. Therefore, following the 2021 notional specification will already deliver some improvement on the 2013 TER, but an even greater improvement to these fabric and airtightness values is encouraged. Part L 2021's limiting value for air permeability is ≤8 m³/(h·m²). This is not very high airtightness. Instead, the Council's recommended air permeability for non-domestic development is <5 m³/ (h·m²), and its preferred value is <3 m³/(h·m²). These reflect notional building airtightness values of Part L 2021 depending on the type of activity undertaken in the building. |
|
Lighting |
Yes |
Low-energy lighting is an investment that tends to pay itself back very swiftly through operational energy savings. LED lighting is far more durable than Compact Fluorescent Lamp (CFL) or incandescent bulbs, allowing savings in cost and embodied carbon during their lifetime through delaying the need to replace them. Low-energy LED lighting throughout all non- domestic buildings is recommended. |
|
Ventilation and cooling |
Yes |
Where the building's use allows, natural ventilation (with opening windows located to enable cross- ventilation) or mixed-mode ventilation with an element of natural ventilation is preferable. When combined with appropriate shading, this can avoid the need for active cooling. Where it is unavoidable to use some active cooling, it is recommended to provide this with heat recovery (most likely for hot water uses), and to provide any active cooling through a reversible heat pump system so that the building also benefits from the most efficient available heating option. |
|
Heat recovery and heat recycling |
Yes |
Where there is active ventilation and/or active cooling, there is potential to recover heat from the outgoing air and to reuse this to heat either incoming fresh air or hot water, thus reducing the need for mains energy for these. The typical method is MVHR (mechanical ventilation with heat recovery). Wastewater heat recovery (WWHR) systems can also have great potential in non-domestic buildings that have a significant hot water load, such as from showers, laundries, frequent hand washing, etc. These are likely to include hotels, gyms, healthcare, schools, and offices/places of work if these have showers. Mixed-use schemes may bring opportunities to recycle heat rejected by active cooling (e.g., in offices/server rooms) as domestic hot water elsewhere in the development. |
|
Heating (for space heat and hot water) |
Yes |
The efficiency assumption for a gas boiler in Part L 2021 for non-domestic is circa 86% to 93%. Air-source heat pumps can achieve efficiencies of >300% and ground-source heat pumps can achieve 300- 400%. This is achieved by taking heat from natural ambient outdoor sources, using a smaller amount of electricity to transfer this into the home. The efficiency is termed the 'SCoP' (Seasonal Coefficient of Performance) or SPF (Seasonal Performance Factor). This refers to the average efficiency across the year, as heat pumps run more efficiently when the 'source' is warmer (typically summer). Heat pumps can be reversible, allowing the development to have cooling in summer as well as benefitting from the excellent heating efficiencies in winter. |
15 Currie & Brown on behalf of Committee on Climate Change (2019), The costs and benefits of tighter standards for new buildings. www.theccc.org.uk/wp- content/uploads/2019/07/The-costs-and-benefits-of- tighter-standards-for-new-buildings-Currie-Brown-and- AECOM.pdf
16 HM Government Department for Levelling Up, Housing and Communities and Ministry of Housing, Communities & Local Government (2023) Building Regulations Part L ("Conservation of Fuel and Power Approved Document L) 2021 edition incorporating 2023 amendments. https://assets. publishing.service.gov.uk/government/uploads/ system/uploads/attachment_data/file/1133079/ Approved_Document_LConservation_of_fuel_ and_powerVolume_1_Dwellings2021_edition_ incorporating_2023_amendments.pdf
17 HM Government Ministry of Housing, Communities and Local Government (2021), Future Homes Standard consultation response. ("Summary of consultation responses and Government response"). https://assets. publishing.service.gov.uk/government/uploads/system/ uploads/attachment_data/file/956094/Government_ response_to_Future_Homes_Standard_consultation.pdf
18 BRE (2022), England NCM Modelling Guide 2021 edition (Sep 2022). Available from UK National Calculation Methodologies website. www.uk-ncm.org.uk/download.jsp?id=35