Purpose The Environment Agency estimates that one in six homes in England (approximately 5.2m properties) are at risk from flooding and 185,000 commercial properties are located in flood-prone areas. Further, an estimate of 10,000 new homes are built on flood plains yearly. The UK has witnessed a significant increase in flood events over the past 10 years. During this period, there has been growing research attention into measures to mitigate the effects of flooding, including the benefits of deploying sustainable urban drainage systems (SuDs) in new developments or as a retrofit. The purpose of this paper is to present the development of a cost-benefit analysis model for the retrofit of SuDs focusing on the potential for improved flood risk mitigation in the context of commercial properties. Design/methodology/approach A synthesis of flood risk management and SuDs literature is used to inform the development of a conceptual cost-benefit analysis model for the retrofit of SuDs and focusing on the potential for improved flood risk mitigation in the context of commercial properties. Findings SuDs have been applied successfully in different parts of the world; however, the uptake of SuDs, in particular, the retrofit of SuDs, has been restricted by a number of issues including a lack of experience and trust in their performance and a lack of understanding in their true benefits. In particular, there is the limited experience of retrofitting SuDs and there are no well-established procedures for evaluating the feasibility, value or cost effectiveness of doing this. Social implications This offers the potential to support the UK government’s flood risk management policy by helping to increase the resilience of properties, whilst offering other benefits to communities such as improvements in air quality and biodiversity and also presenting a clearer understanding of the monetary and non-monetary implication to owners of commercial properties for a more informed and acceptable uptake of SuDs retrofit. Originality/value The proposed model will allow a more comprehensive understanding of the costs and associated benefits associated with SuDs retrofit, highlighting the flood risk mitigation benefits that might accrue over a period of time for commercial property.

The retrofit of Sustainable Drainage Systems (SuDS) has been applied successfully to properties to help mitigate future flooding and to deliver other benefits to properties, such as improvements in air and water quality, economic benefits and improved business reputation. However, the uptake of SuDS retrofit has been low due to a lack of understanding of the true costs and benefits and concerns about long-term maintenance. This study presents a cost-benefit analysis (CBA) of the monetary and non-monetary values of SuDS retrofit in the context of an individual property, in this case, a leisure centre. A qualitative study was carried out comprising a series of interviews with stakeholders to the property, an analysis of documentary evidence and observations on the site. The findings demonstrate the importance of teamwork amongst the stakeholders during the decision-making process in helping to overcome many of the known challenges. The willingness to pay process is used to value the tangible and intangible benefits arising from the scheme. The installation would provide a net value to the client of well over £100,000 over a 10-year period versus the installation costs of £39,000 and the return on investment would be achieved in just 3 years. The findings highlight many of the apparent barriers that need to be overcome when installing retrofit schemes and clearly demonstrate the importance of the intangible benefits derived. It is recommended that these are given full consideration at the decision-making stage and in supporting the uptake of the retrofit of SuDS.

Sustainable Urban Drainage Systems (SuDS) are known to help mitigate flooding whilst simultaneously delivering other positive outcomes, such as the provision of environmental, economic, educational, and business benefits. Despite this, there has been a relatively low uptake of SuDS in new developments and even less of an uptake in the opportunities for retrofitting SuDS in existing buildings. A major barrier to uptake has been a lack of understanding regarding the value of the benefits provided by SuDS. This study presents an appraisal of the costs and benefits derived from the retrofitting of SuDS in existing buildings and reveals some of the key decision-making considerations during the design and installation of such schemes. A qualitative research approach that included a number of case studies of successfully retrofitted SuDS schemes within public buildings was conducted. A novel feature of the research was the use of the Willingness to Pay (WTP) approach to value the tangible and intangible benefits provided by the various schemes from the perspectives of the property owners. The findings revealed that the retrofit provided a net value to the client of over £100,000 over 10 years, a mean CBA ratio of 5.3/10, and a return on investment (ROI) that would be achieved in less than 3 years. The importance of stakeholder engagement during the decision-making process was highlighted in helping to overcome many of the design, installation, and maintenance challenges. The findings demonstrate a significant ROI for these SuDs retrofit schemes and highlight useful approaches to overcoming the barriers in valuing the importance of the intangible benefits. In supporting the uptake of the retrofitting of SuDS, it is recommended that these benefits are given full consideration by property owners, urban planners, and architects during the design of retrofit schemes and throughout the decision-making stage.