Building on brownfield: costs and considerations

The environmental, social, and cost advantages of regenerating previously used land can be significant. However, there are important factors to consider when turning old sites into new prospects. AECOM’s Paul Wilcock, Lynda Brooks, Rob Mayes and Philip Mackintosh explore the factors influencing brownfield development.

Developing land which has previously been built on – brownfield sites – is arguably unavoidable in the UK. Greenfield land is limited, and protecting what remains of it curbs carbon emissions, supports natural habitats and air quality, and prevents unnecessary urban sprawl.   

In contrast, brownfield land is plentiful across every region of England, the Countryside Charity (CPRE) says. The organisation, which assesses and tracks land development, claims areas particularly ripe for redevelopment include the north west, with capacity for 167,461 new homes on brownfield sites, Yorkshire and Humber (108,790 homes) and the west Midlands (99,600 homes).  

There is a political imperative to using brownfield sites for building. The government is committed to its ‘levelling up’ agenda, boosting the economy through housebuilding and renewed industry throughout the UK. Regenerating poor quality or abandoned industrial and residential sites in under-supported regions is a clear means of achieving this.  

Despite these benefits, the CPRE says the UK lacks a truly ‘brownfield first’ approach to planning policy. Countryside is often bought and built on without brownfield land being considered.  

Given the clear environmental and socioeconomic benefits to re-deploying derelict land, why are we still building on virgin soil? A combination of reasons – not least the fact that when working with brownfield land, developers cannot start with a blank slate.  

Establishing what’s there

Typically, brownfield sites are remediated for one of two reasons. The first, a statutory obligation to clear up contamination, or secondly, to redevelop the site to unlock its commercial potential. In the latter case, for the project to be financially viable, location matters. 

Gaining insight into unidentified utilities – averting the potential for hitting one of the tens of thousands of pipes, cables and power lines snaking underneath the UK – is one of the biggest hurdles when preparing brownfield sites for redevelopment.  

If the site’s history is not initially known, detective work can provide clues. Old maps and road names often reveal the land’s previous uses and what may linger beneath the surface. 

Desk research is critical to building a basic idea of what to expect with a certain site.  

However, it can only reveal so much about what is on the site, and the extent of the challenges. Until ground is broken, it is impossible to build a complete picture. Brownfield sites often contain or interact with decades or even centuries-old existing elements, which have migrated underground over time. Upfront ground investigation work can be costly, but doing more early on can pay dividends in the long run.   

Cleaning up contamination

Contamination – and the cost and difficulty involved in remediating it – is one of the primary reasons potential regeneration projects fail to reach fruition. The UK’s industrial past means brownfield sites can contain a host of contaminants, often presenting unexpected challenges.  

When dealing with land contamination, a remediation strategy needs to be developed by a geotechnical engineer who will assess if treatment is possible, or if the contaminated matter must be removed.  

The ability to treat contamination in situ depends on the type and amount of contamination in the soil. Many contaminates are threshold-based – if the level can be reduced sufficiently, it can stay. A geotechnical engineer will assess suitability for treatment, but some materials simply cannot be removed. Asbestos, for example, cannot be treated once asbestos fibres have infiltrated the soil. 

When addressing these issues, maintaining a positive public perception is vital. Effective, timely communication is extremely important to ensure people in the vicinity understand the risks and the benefits of a project and to avoid scaremongering. 

Cost considerations

Designing in a sympathetic way to avoid some of the challenges encountered when developing brownfield sites can have a significant bearing on cost. 

The cost of remediating contaminated land is driven by the type and extent of the contamination. Contamination in isolated spots is easier and cheaper to treat than contamination affecting a whole site.  

Offsite disposal costs also depend on the contamination type. Not all landfill sites accept all types of contamination, which can mean additional transportation costs. The most dangerous contaminants also attract landfill tax.   

With regards to contamination, of the materials or chemicals in question are costly or difficult to dispose of, it can be cost effective to minimise cut and fill across the site. This may influence decisions to have basements and will influence the foundation solution. 

When dealing with existing live utilities, pragmatism and flexibility can pay dividends. If existing mains connections are discovered, adapting the design by adjusting the site layout or development configuration can be an easier and more cost-effective solution than disabling and re-routing connections.  

Conclusion

Choosing brownfield sites over greenfield land can undoubtedly add layers of complexity to project development. The challenges may be substantial, but in the race to reach net zero carbon emissions as a country by 2050, we simply cannot afford to ignore the opportunities and carbon-reducing potential of brownfield sites. 

At present, the benefits of building on brownfield rather than the UK’s shrinking green belt land are not seized upon enough by the state, local councils or by commercial developers. There is a mismatch between official statements and what happens in reality; some councils, for instance, have declared a climate emergency, and yet continue to develop housing projects on greenfield land. 

The CPRE calls for a “comprehensive brownfield first policy” amongst both government and industry. It is possible that we will look back on this period with shock that greenfield land continues to be used. As the impacts of climate change become even more stark, a near future where projects will have to be brownfield to be considered sustainable is not out of the question.