Viability assessments were introduced in the UK to encourage more homes to be built in an uncertain financial landscape. In local government, viability assessments can see councils lose out on affordable homes at the expense of developer profits, a common challenge faced by Southwark Council.

We started this project to find a better way of evaluating viability assessments that would level the playing field between councils and developers. The council aimed to meet targets that would see up to 35% of affordable homes generated through new developments.


From the discovery phase, we identified why viability assessments aren’t working and what we can do about it. Through stakeholder interviews, we found evidence of a power imbalance between councils and property developers. Viability assessments are often used as a negotiation tool, resulting in high costs and delays to the planning application process. There’s also no standardised assessment format, rather, they’re manually compiled from the ground up each time and are not regulated to professional standards.

Working in a multidisciplinary team, including experts in service design and data science, we conducted qualitative and quantitative research and analysis to explore the data and data sources involved in compiling viability assessments and the current tools and systems used. This allowed us to develop a comprehensive map of the as-is process, including pain points, data flows and timescales.

From understanding the as-is process, we mapped what the ideal future state of viability assessments in planning might look like to meet needs and deliver more affordable homes.

Southwark Council viability assessments end to end study illustration

With this evidence base, councils would be prepared to confidently negotiate more affordable homes. Alongside this future vision we created a series of prototypes to visualise points in this journey, such as when:

  • developers sense check early viability figures against the council’s expectations
  • developers submit viability information to the council
  • council officers review submitted information against comparable developments

We developed a working data prototype to prove what’s possible in terms of triangulating data from third-party sources to give a view of sales values for developments of a given size within a given area. This data prototype brings together two live datasets to suggest if property prices are within the expected range.

Southwark Council viability assessment property checker early working data prototype

We created two further design concepts that illustrated how the viability assessment process could be improved to negotiate more affordable homes.

The viability assessment checker is a tool to support developers when they’re building their planning application. The applicant can input figures and the tool identifies whether the application might be rejected or take longer to process. This tool will not only establish expectations for developers about their application and discourage applications with disproportionate costs and values but also standardise the collection of this viability data for future use both within this process and elsewhere.

The review and comparison tool enables council officers to investigate applications in more detail, choose sites to compare a submission to and export scenarios to support negotiations.

A Southwark Council tool that would enable council officers to look at viability assessments in context with comparable sites

These tools capture viability information in a standardised format and present it back in context. This results in quality targeted negotiations with developers to increase affordable housing on new developments.


Following the discovery phase, we came together with London Borough of Southwark, and three new partners, Connected Places Catapult, The London Borough of Tower Hamlets and The Greater London Authority, to test insights and assumptions with case officers, viability officers, consultants and developers. The question we were looking to answer was, ‘how might we embed new tools and approaches to harness the value of data?’ And:

  • make viability more accessible
  • put councils on an equal playing field with developers
  • maximise the delivery of affordable homes
  • enable further innovation in the planning sector

Testing has led to prioritising the comparison tool, called the Viability Comparison Tool. This tool enables council officers to:

  • search and filter to identify comparable sites using key information
  • view detailed information of selected sites side by side for comparison
  • sense check submitted figures and proposed levels of affordable housing

With this data, council officers are equipped with the insight and support to negotiate higher levels of affordable housing.

Southwark Council alpha prototype tool of the viability comparison tool
Southwark Council example of the comparison list extract

Because no viability data standards currently exist, throughout alpha we tested whether we could create an initial data standard that would help us to:

  • build and test our prototypes
  • allow us to investigate the wider value of consistent viability data
  • engage with the wider planning data standards community
  • accelerate work in a future beta phase

We worked with viability and planning experts to prioritise and select the most important variables for initial inclusion. This resulted in the creation of a data schema for viability - a shared, standardised way of capturing, storing and presenting data. Making things machine-readable allows for much easier transfer and analysis of data and easier comparison of applications to other developments. An open, standardised database also allows the PlanTech sector to develop new innovative, interoperable tools.

We also learned about the skills and capabilities of the in-house viability and planning teams to analyse and interpret data and tools. Through testing sessions, we understood the level of knowledge and expertise required to take on viability assessment tasks and reduce reliance on viability consultants from pre-application, through to the assessment and review process.

Together with the partner organisations, we built an overview website of the viability alpha with a further overview of the project and its outputs.


The discovery phase created a shared understanding of opportunities by visualising the end-to-end process of viability assessments in one place for the first time. With Southwark Council, we identified the need for a number of products and services, supercharged by quality data to negotiate more affordable homes for neighbourhoods.

Concepts were designed to meet the needs of both the council and developers, despite differing objectives. Indicative cost and efficiency savings were identified through streamlining internal systems and processes.

I’m really impressed with how you’ve taken this from a vague idea into a fully formed concept and engaged so many people in the process.


Southwark Council

Through the Alpha phase, we created an initial database of existing developments complete with viability data, to support development and testing of the comparison tool prototype. As well as enabling use of the comparison tool, it’s the first time this data has been brought together in one place for local authorities, and the Old Kent Road team in Southwark are already using the data to assess incoming applications in that area. Further, there is a strong desire from the extended PlanTech community to have access to this standardised data for purposes wider than finding comparators.

Development data is the true underpinning enabler of innovation in this space, enabling products such as the comparison tool. We’ve also designed a data capture form in line with our viability data schema, allowing crucial figures about incoming applications to be stored, helping to build the database. An open, standardised database allows the PlanTech sector to develop new innovative, interoperable tools.

I’m really pleased with how this phase has worked. This sort of collaborative effort across multiple agencies isn’t easy.

Planning Officer

Southwark Council

The potential impact of this work for local authorities, the wider PlanTech community and the public is significant. Connected Places Catapult commissioned research shows that every five years when making the Local Plan, local authorities spend on average £237,000 collecting viability evidence. The majority of this cost is from buying viability datasets. When the database is operational, this cost could be reduced by 75%, saving authorities £178,000 every 5 years.

Through better data capture, surfacing information through the comparison tool and allowing officers to sense check and interact with viability, this could reduce current negotiation time considerably. If negotiation could be reduced by 30-40% this could save 265-353 officer hours per year to be repurposed to value-adding activities.

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