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Last edited 19 Nov 2020
Additionality of built developments
The concept of ‘additionality’ is used to identify the net (rather than gross) impacts resulting from an activity or project, that is, ‘...the extent to which something happens as a result of an intervention that would not have occurred in the absence of the intervention’ (ref English Partnerships Additionally Guide: A standard approach to assessing the additional impact of interventions). It is sometimes taken only to relate to positive impacts, however, this assumption would pre-judge the outcome of an assessment as most projects will have both positive and negative impacts.
Additionality is often used in the context of regeneration, regional development, local economic growth and housing interventions, adopted as an assessment tool for large-scale projects by the government. However, it can also be used to assess applications for funding, for individual programmes or projects, or for specific impacts such as greenhouse gas emissions.
Additionality can be used as a decision making tool, helping test and compare options and to assess where changes may be necessary. Assessments can be carried out throughout the development of a project, however, the greatest opportunities for change resulting from an assessment will come earlier rather than later.
Assessments may consider impacts such as:
- The quantity of outputs in an area.
- The consequences of impacts happening sooner than they would otherwise have done.
- Quality impacts.
- The benefits for target groups.
Impacts can be assessed from the top down, looking at general indicators of the impact of an overall intervention, such as local employment, or bottom up, assessing the impacts of specific actions. It may be appropriate to use both techniques to gain a clear understanding of the impacts of an intervention.
Assessments need to consider options in relation to what would have happened in the absence of the intervention (the reference case). This is not simply a matter of comparing options with the current position, as that position might change if the intervention were not to take place. For example, it may not be possible to simply do nothing, and alternative interventions may occur in the absence of the proposals. It is also necessary to consider external impacts that may be caused by the intervention but are not directly part of the project, for example, investment in an area may encourage further investment by third parties. Conversely, providing a new service may result in cost or price changes, may impact on existing services, or prevent alternative providers from offering the service.
Assessment can be used to help maximise impacts, while ensuring that the minimum resources are used to bring about those impacts. Where the impacts would not have happened at all without the project, it can be considered 'fully additional'. Where excessive resources are consumed to deliver the impacts, this is referred to as ‘deadweight’.
NB The Green Book, Central Government Guidance On Appraisal And Evaluation, Published by HM Treasury in 2018, defines additionality as: ‘…a real increase in social value that would not have occurred in the absence of the intervention being appraised.’
 Related articles on Designing Buildings Wiki
 External references
- English Partnerships, Additionally Guide: A standard approach to assessing the additional impact of interventions. 2008
- Homes and Communities Agency, Additionality guide. 2014
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