The definition of zero carbon for eco-towns set out in the Planning Policy Statement (2009) is that, over a year, the net carbon dioxide emissions from all energy use within the buildings on the eco-town development, as a whole, are zero or below. The initial planning application and all subsequent planning applications for the development of the eco-town should demonstrate how this will be achieved.
The definition excludes embodied carbon and emissions from transport but includes all buildings – not just houses but also commercial and public sector buildings which are built as part of the eco-town development.
From November 2018 to March 2019, UKGBC brought together an extensive range of industry stakeholders, including a task group, to build consensus on a framework definition for net zero carbon buildings in the UK.
The primary focus of the framework is to set in place a path to achieve net zero carbon buildings in both construction and operation (in-use energy consumption), whilst beginning to provide direction for addressing whole-life carbon in the industry.
The Framework definition of Net Zero Carbon Buildings consists of two definitions:
1. Net zero carbon – construction (for new buildings and major renovations). When the amount of carbon emissions associated with a building's product and construction stages up to practical completion is zero or negative, through the use of offsets or the net export of on-site renewable energy.
2. Net zero carbon – operational energy (for all buildings in operation). When the amount of carbon emissions associated with the building's operational energy on an annual basis is zero or negative. A net zero carbon building is highly energy efficient and powered from on-site and/or off-site renewable energy sources, with any remaining carbon balance offset.
A third definition, 'new zero carbon – whole-life' is also proposed at a high level, but further work is needed to develop the detail of this approach.
The framework includes five steps, shown in diagram below. Some of the steps are relevant to the definition for construction and some to the definition for operational energy. However, a building targeting net zero carbon for construction should be designed to achieve net zero carbon for operational energy.
Each step has a set of principles that have been ordered in terms of priority and should be reviewed in that order. Each principle sets out the approach that should be followed, including a rationale for the principle, associated technical requirements and, where relevant, any areas for future development.
Broadly speaking the definitions seek to:
1) ensure that a whole-life carbon assessment is undertaken,
2) prioritise reductions in energy demand and consumption over all other measures,
3) report annually on in-use energy consumption,
4) prioritise on-site renewable energy sources and require any off-site renewable energy to demonstrate additionality,
5) offset any remaining carbon using a recognised offsetting framework and publicly disclose this.
The London Energy Transformation Initiative (LETI) was established in 2017 to support the transition of London's built environment to net zero carbon, providing guidance that could be applied to the rest of the UK.
A network of over 1,000 built environment professionals have worked collaboratively to compile evidence-based recommendations for London Plan and London Environment Strategy policies. The LETI Climate Emergency Design Guide defines what good looks like in context of the climate emergency for new buildings.
The guidance focusses on delivering net zero carbon new buildings which means having regard to whole-life carbon, which in the context of the document means;
i) Operational carbon – net zero operational carbon means that buildings burn no fossil fuels, are 100% powered by renewable energy and achieve a high level of energy performance in line with national climate change targets.
ii) Embodied carbon – The carbon emissions emitted producing a building's materials, their transport and installation as well as disposal at the end of life.
A key recommendation of the guidance is that the Energy Use Intensity (EUI) of a building should replace carbon emission reductions as the primary metric used in policy, regulations and design decisions. EUI is an annual measure of the total energy consumed in a building. EUI is regarded as a good metric as it depends on how the building performs in use.
EUI includes all the energy consumed in the building including regulated energy (heating, hot water, cooling, ventilation and lighting) and unregulated energy (plug loads and equipment e.g. kitchen white goods, ICT and AV equipment). It does not however include charging of electric vehicles.
The guidance makes recommendations for operational energy which includes the fabric efficiency of building materials, window areas and energy consumption. It also makes recommendations for embodied carbon emissions.
To achieve Net Zero Operational Carbon, LETI propose ten key requirements for new buildings:
1) Total energy use of different building typologies not to exceed Energy Use Intensity (EUI) targets for energy uses in buildings including regulated and unregulated energy.
2) A fabric first approach ensuring that space heating demand for all building types is below 15kWh/m2/yr.
3) Annual energy use and renewable energy generation to reported for the first year post completion as part of a measurement and verification process.
4) Embodied carbon of construction materials should be assessed to reduce impacts of construction process.
5) Heating and hot water should not be generated from fossil fuels.Average annual carbon content of heat supplied (gCO2/kWh) should be reported.
6) On-site renewable electricity should be maximised.
7) Energy demand response and storage measures should be incorporated, and the building annual peak energy demand should be reported.
8) An annual carbon balance calculation should be undertaken to demonstrate that a building achieves a net zero carbon balance.
9) Any energy use not met on-site should be met by investment into additional renewable energy capacity off-site.
In addition to different definitions for net zero carbon development, it is also useful to consider circular economy principles and how these relate to resource consumption, waste and carbon emissions.
A circular economy keeps products, components and materials at their highest use and value. In a circular economy, every item or material is useful and valuable to another part of the economy. It provides an alternative to the current 'linear' economy – in which we make, use and dispose of products, components and materials and recover little value from them.
Significant greenhouse gas emissions arise from consumption habits in society. A circular economy seeks to shift away from a linear pattern of resource extraction, use and wastage to one in which products and materials are retained and used at their highest use value for longer through maintenance, repairs and upgrades.
As construction waste accounts for the largest proportion of waste within the Oxfordshire waste cycle, circular economy principles are relevant to the Oxfordshire Plan, particularly efforts to achieving net zero carbon emissions through the design and construction of new development.
The use of natural or recycled materials in construction, designing buildings for adaptability and changing uses over time as well as the ability to dismantle and recover materials at the end of a building's life would all help to minimise resource extraction and waste arising from construction in Oxfordshire.
This would help to minimise carbon emissions associated with construction and development over the lifetime of the Plan.
Consideration of circular economy principles through the Oxfordshire Plan has potential to deliver a wide range of benefits beyond tackling waste and reducing carbon emissions with positive social implications, new jobs, improved skills and new business opportunities.
To include in the Oxfordshire Plan a policy setting out sustainable design and construction requirements to be applied to major residential and non-residential developments within Oxfordshire.
This policy would be subject to viability and deliverability testing but with the objective to achieve net zero whole-life carbon for both residential and non-residential buildings, taking account of embodied carbon, low energy use and renewable energy supply.
Developments should be fossil fuel free and fossil fuels should not be used to provide space heating, hot water or fuel for cooking. Demand for energy should be balanced by the provision of on-site renewable energy generation.
Carbon offsetting would only be permitted where it is demonstrable that net zero carbon cannot be achieved on site.
A financial contribution based on defined calculation would be made to carbon offsetting projects including off-site renewable energy generation or carbon sequestration consistent with defined natural capital and nature recovery approaches defined in the Plan.
Buildings should be designed to be resilient to the effects of a changing climate, including overheating.
New buildings should be designed to be durable but flexible and adaptable to changing needs over time.
Residential and non-residential buildings should be designed and built to maximise the use of natural or recycled material in construction and to enable disassembly at the end of a building's life in accordance with circular economy principles.
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