Engineering Grey Belt Viability

While brownfield development remains a major focus in response to the housing crisis, the emergence of grey belt is something that should fill developers, local authorities and construction professionals alike with a sense of opportunity and untapped potential. Despite the definition of grey belt still being debated, and sites likely to be assessed on a case-by-case basis, it’s clear that the target is poor-quality land within the green belt that could be put to better use – and in that sense it shares similar characteristics to brownfield land. This means many of the lessons learned from successful brownfield regeneration can be applied, with grey belt sites potentially offering multiple advantages due to their inherent connectivity and prospect of coalescing with established communities.

The government identified a disused petrol station as an example of a green belt site that previously wouldn’t have been considered a viable redevelopment opportunity for housing because of its designation. Under new plans, the government is expected to lift restrictions on redevelopment of these types of sites, but just because there is a greater prospect of gaining planning permission doesn’t mean they are viable.

Some of the main challenges to viability of grey belt sites can be hidden underground, where potential contaminants mean a remediation strategy will be the first priority in making them suitable for human habitation. The prospect of demolition and subsequent remediation of an abandoned petrol station will be daunting for many, but with the right engineering advice, development potential can be unlocked and assumed complexities can be overcome.

Even if an abandoned petrol station was outside of the green belt, it would be unlikely to attract many suitors willing to take on the challenge of enabling works given the size of these sites means a modest yield from the limited number of houses they can accommodate. Instead, we look towards landfill sites and quarries as more attractive propositions.

As an example of a more valuable proposition, one of the UK’s largest landfills sits just outside of Birmingham, spread over almost 200 hectares within the green belt but no longer serving its original purpose after closing in 2015. The most recently filled areas of the site are likely to need time to stabilise, but the original landfill areas should be stable enough that with a robust engineering strategy they can be made fit for a new purpose. If developed for housing, there is an economy of scale that should more than compensate for the exertions of the necessary enabling works. Being able to build a large number of homes on one site means that the sequence of development can be streamlined and new homes can be brought to market more efficiently.

A robust foundation solution and capping-off of contaminants are some are the main considerations from an engineering perspective when working on a landfill site, but successful landfill regeneration projects completed on land categorised as brownfield prove it can be done with the right expertise, investment and innovation.

Landfill sites surrendered since the late 1990s will have had at least 25 years to reach a sufficient level of stability, for both ground and gas, making the complexity of building on them well worth evaluating, but that’s not to say they will all pass the test. Many of the types of sites we expect to see categorised as grey belt will be viewed as constrained in one way or another, but just because it has a sullied past doesn’t make it unviable. Engineering solutions are available and perceived challenges can be overcome with the right techniques and approach. It all starts with a thorough ground investigation, followed by insightful collaboration between developers, contractors and engineers.

On top of the government’s overarching housing target, each development will need to consider wider priorities, from biodiversity net gain to community impact through social value initiatives. While it all sounds like a big, complicated challenge, we want to reassure developers and local authorities that quality engineering consultancy can increase grey belt viability – helping to establish the foundations for successfully meeting the UK housing demand.