Triaging Tree-Related Subsidence: An Insurance Perspective

Local Surveyors Direct estimated that subsidence claims over the last 10 years have cost the insurance industry between £140-400 million annually. A significant proportion of these claims will be due to tree-related subsidence, where tree roots and vegetation extract moisture from shrinkable clay soils, causing movement and structural damage to buildings.

While there are several strategies for treating tree-related subsidence, the process can be complex with insurers needing buy in from surveyors, ground engineers and local authorities to evaluate the problem. Here, Freya Chapman, Residential Lead at ground engineering specialist Mainmark, explains how insurers can adequately and efficiently triage tree-related subsidence.

The current process

Subsidence claims are notoriously complex, particularly if responsibility for managing the tree lies with a neighbour, local authority or housing association. If a resident suspects they have subsidence in their home caused by vegetation managed by a local authority, the insurance claim will be delayed while evidence is gathered as to the ‘root’ of the issue. This could be anything from tree roots extracting excessive moisture (common with oaks, poplars and willows), or tree roots damaging drains, causing leaks and soil washout.

Tree Preservation Orders (TPOs), placed on trees older than 15 years, are another delaying factor, further limiting the solutions to the subsidence claims. Simply removing the tree isn’t sustainable practice and could destabilise the soil further. So, when a subsidence claim is accepted, it is the responsibility of the insurer to investigate a solution through loss adjusters and engineers.

Importance of Framework Agreements in Triaging Subsidence

As an insurer or loss adjuster, having a ‘go-to’ set of approved suppliers could really help speed things along – helping residents obtain a resolution to their subsidence efficiently, assisting in evaluating the severity of the problem and mitigating the costs of ongoing claims.

The standard process for a ground engineer is to monitor the subsidence in a home over a period of time, through a series of visual inspections, crack and level monitoring, site surveys and, in some cases, in-situ assessments to test soil samples.

While this paints an important picture of the conditions contributing to subsidence, these can change quickly when vegetation is involved, and the process of monitoring can take upwards of 12 months. Tree roots will spread deeper and wider to obtain moisture from the soil, particularly during periods of drought, resulting in more clay shrinkage and bigger insurance payouts. Equally, if settlement has contributed to clay shrinkage – the process the ground adjusting to support the weight of a new home – a homeowner might not even be covered for the structural damage under their traditional home policy.

Payouts in 2022, following the hottest UK summer on record, reached £219 million according to the Association of British Insurers, the highest annual subsidence payout since 2006. Therefore, to adequately manage losses and mitigate the damage caused by tree-related subsidence, its critical insurers have the right expertise for treating surrounding vegetation.

Treating Subsidence

Treating tree-related subsidence sustainably must also be a priority for insurers and loss adjusters. Where regional or local legislation often prevents the removal of trees, root barriers, some of which are made by pouring concrete into a PVC mesh system, are used to prevent the tree’s roots from spreading further. Generally, cementitious root barriers are costly, time consuming and bad for the environment.

Underpinning, where the soil beneath the existing foundation is dug out and further cementitious material is used to extend the foundation, can also treat tree-related subsidence in severe cases. This isn’t used as much nowadays, with piling being a slightly less-invasive solution.

These techniques are effective and can be done quickly to stabilise a home and settle a claim. However, Mainmark believes there is a less resource-intensive, greener way to treat clay shrinkage expediated by tree roots, dealing with more the structure and the tree. Adopting a combined methodology can provide a way forward for insurers and their partners.

For Mainmark, combined methodology when treating tree-related subsidence is the process of establishing harmony between the built and natural environments. In recent years, ground engineers have made progress in developing textile-based root barriers using copper, the only compound that tree roots naturally divert away from. To be installed, textile-based root barriers require a thinner access point compared to cement-based treatments and are far greener and less invasive.

While there is still research to be done on solving subsidence claims sustainably, there is more than 17 years’ worth of data to suggest that copper root barriers could provide a solution. To manage losses, mitigate further subsidence claims while protecting the surrounding vegetation, insurers should consult with ground engineering experts who can adopt a problem-solving approach using state-of-the-art technologies to meet both project and client requirements.