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Westminster environment guidance - Section B

Find information on carbon and pollution reduction, as well as urban greening.

Section B - Carbon Emission Factors

The current UK regulatory framework within Approved Document L of the Building Regulations uses carbon emissions as the basis to determine compliance under the Standard Assessment Procedure (SAP). The carbon produced by new buildings is estimated using Carbon Emission Factors, which are periodically updated to reflect the changing carbon intensities of fuel supply.

The GLA encourages the use of SAP 10 in new buildings where the development is not going to be connected to a planned or existing heat network. Developments in Westminster that are seeking to connect to an existing or proposed network should continue to use SAP 12 so that the benefits of a heat network are appropriately reflected in energy calculations. For further guidance, please refer to the GLA’s Draft Energy Assessment Guidance 2020.

Alternative metrics

There are a number of unintended consequences in using the existing Part L methodology to determine the performance of a development, most notably that the carbon intensities of energy supply can incentivise the use of mechanical systems over the improvement of on-site efficiency measures, contrary to the aims of the energy hierarchy.

We therefore encourage developers to provide alternative metrics and targets, as advocated by the London Energy Transformation Initiative, that better reflect operational energy demands of the development and support the fabric first principle. This includes:

  • energy use intensity (kilowatt hours/m2/year)
  • space heating demand (kWh/m2/year)

Building Management Systems

Building Management Systems (BMS) can be an important tool in monitoring and regulating energy use in developments.  BMS are available for developments of various scales and as the operation of the building accounts for the vast majority of emissions, they are now an important component of climate resilient buildings.  Operator error can be significant, so it is essential that building managers receive appropriate training to maximise efficiency.  Small systems for residential units are increasingly popular and can be an effective option for homeowners to manage financial outlay and carbon emissions.

Carbon Offset Fund

In planning terms, a site is deemed to be financially viable if the value generated by developing it is greater than the cost of developing it. The cost of the land, landowner premium and other factors are taken into consideration when a financial viability assessment is carried out. National guidance on planning also states that financial viability should not compromise sustainable development. The impact of a development is mitigated through planning obligations. This is a binding and enforceable legal agreement that is deemed to be necessary to make a planning application acceptable in planning terms. Carbon Offset is the planning obligation associated with mitigating the impact of carbon emissions generated in a proposed development which is expected to be delivered through on-site interventions. 

Carbon offsetting is a planning obligation collected under Section 106 Planning Obligation process that allow new developments to comply with local planning policy where it is not feasible or practical to achieve all necessary carbon emissions savings at the development site. This is collected as a financial contribution and ring-fenced to fund carbon saving projects elsewhere in the local authority area, helping to ‘offset’ the carbon footprint of the new development.

Carbon offset payments are collected as a last resort when residual carbon emission performance in a proposed development cannot be achieved on site through the Be Lean, Be Clean and Be Green stages shown in the energy hierarchy. It is set at a level that reflects the cost of addressing the residual emissions.

Carbon gap (residual tonnes of carbon) x price per tonne of carbon (£) x 30 years (lifespan of the building services)  =

Carbon Offset Contribution

As part of the energy statement submitted to support the planning application, the tonnes of carbon that are not mitigated have a carbon price attributed to them in accordance with the GLA’s methodology. The council’s forthcoming Affordable Housing and Planning Obligations SPD will provide detailed information of the breadth of planning obligations that may be applied to a planning application.  The council will regularly review and update the local cost of carbon and will be viability tested.

Westminster’s carbon offset funds are managed in accordance with the existing processes for allocating planning obligations and funding bids determined by the council’s Cabinet CIL Committee.

Carbon offset fund guidance
Carbon offset fund guidance PDF, 695.02 KB, 14 pages

It sets out the how the offset price is calculated, the current cost of carbon and how the carbon offset fund will be spent in the borough. The council will actively promote projects supported through carbon offset contributions to ensure confidence and transparency in the offset process.


Last updated: 16 April 2021