02 Subsidence


The effective management of structural defects, and particularly subsidence of low rise buildings, requires experience, a clear strategy and an effective decision making process. With 85% of all subsidence damage within South East England related to clay shrinkage exacerbated by the action of tree roots our process is designed around this scenario but can be easily adapted for alternative causes. 


The process can be divided into five distinct stages, each of which needs to be completed, or abandoned, before moving forwards to the next. Whilst the simple cases may be resolved within 6 months of notification a moderately complex case can last 18 – 24 months to final resolution. For this reason it is important that there is continuity within the team, avoiding the costs of duplication which are inevitable when the key personnel change. At Richard F Gill & Associates LLP we aim to make decisions about mitigation within 2 -3 months, achieve mitigation at the earliest opportunity and finalise monitoring within 12 months. These time scales are dependent on mitigation.


Stage 1                        Initial inspection and report, identify construction, record damage.

At stages 1 & 2 The Richard F Gill & Associates LLP can offer the experience of Chartered Surveyors and Chartered Structural Engineers with vast experience of structural defects in domestic properties stretching back over the past 25 years.


Stage 2                        Identify the cause, site investigations and vegetation survey.

At Stage 2 the experience of many thousands of similar cases can reduce investigation costs, sometime eliminating the need for expensive trial pits and boreholes and allowing a fast track solution on the simplest of cases.    


Stage 3                        Mitigate cause.

It is at Stage 3 where Richard F Gill & Associates LLP can offer added value to the process with a modern, cost effective, sustainable and above all pro-active approach to case management. In so many cases that we are asked to offer a second opinion it is the mitigation process that delays the rectification of the problem, making the monitoring process one of watching the damage progress rather than stabilise. In many cases expensive and disruptive underpinning can be avoided simply by removing offending vegetation at minimal cost.


The management of vegetation as a means of controlling subsidence events is a proven approach that reduces case duration, reduces case spend and increases customer and stakeholder satisfaction.


When allied to a sustainable tree planting and replacement tree strategy vegetation management compares extremely favourably in regard to sustainable use of resources as against intrusive repair and underpinning options and can be made effectively carbon neutral.


Working closely with a leading team of Arboricultural specialists we have more than 25 years experience in the delivery of integrated mitigation and management strategies for trees in relation to subsidence of low rise buildings. With a thorough knowledge of the case law involving trees we are often able to persuade third party tree owners of the merits of early tree removal and in the case of a knowledgeable tree owner, usually local authority, Network Rail etc, we can build the evidence necessary when seeking the recovery of costs associated with damage caused by the third party vegetation.  


Our approach to statutory controls, Tree Preservation Orders and Conservation Areas, is firm but by necessity flexible. There are some circumstances where tree removal is either too risky in terms of heave damage or simply an unacceptable loss of visual amenity although these cases are rare.


Stage 4                        Monitor building through to stability.

Using a combination of Crack Width monitoring and Precise Level monitoring, now essential where a TPO tree is involved following the advice of The Department For Communities and Local Government, we are able to accurately assess the residual movements within a property with level readings taken to an accuracy of 0.1 mm.


We attempt not to use monitoring as a diagnostic tool, although invariably where a third party or Local Authority are involved this is often the case. In a perfect scenario monitoring would be installed following the initial visit, mitigation would occur soon after and the monitoring would indicate a period of recovery followed by stability, allowing early repairs to be undertaken.


Monitoring should never be used as an excuse to delay the decision making process and is of no use in its own right unless a clear strategy for the building has been devised and implemented.


Stage 5                        Make good damage.  

At Stage 5 our Chartered Structural Engineers have many years experience of repairs and maintenance to residential housing, both occupied and unoccupied, and are able to manage the expectations of the tenants and the contractors to bring the entire process to successful conclusion. Either by the use of agreed schedules of rates, or by competitive tender, our Engineers will ensure value for money and a clear audit trail to demonstrate how this has been achieved.