Subsidence – Part 1 – Not all it’s cracked up to be!

When you see cracking in a building it will not always be, in-fact is very rarely likely to be subsidence.  This can only be established through a comprehensive building survey and detailed investigations

Source: http://www.subsidenceforum.org.uk/

Whilst inspecting buildings I have learned over the years to be very cautious in the terminology I use in the presence of Clients because there are some words that just provoke panic.  Take asbestos for example, or cracking or even subsidence.  These words strike fear into many people mainly as a result of what they have seen on the news or read in the media.  It is fair to say that sometimes these fears can be realised if any of the above examples are found to be present/occurring in a building, however in the vast majority of cases, these issues can be dealt with relatively easily.   This is generally a result of a lack of real understanding, which is why it is always advisable to seek professional advice from a Building Surveyor or Structural Engineer.

When I first graduated from University I joined a Property Consultancy who’s main area of business was dealing with subsidence insurance claims as Loss Adjusters.  My role was to visit site with a more experienced Structural Engineer, who would make an initial assessment, and then I would be required to manage the claim to a conclusion.  This often involved crack monitoring to establish whether any movement was historic (had now stopped) or progressive (was still continuing).  This was a crucial part of the process as it is pointless dealing with the effect of subsidence until movement has been stopped.  On the occasions where movement was found to be progressive, it was often first necessary to undertake substantial remedial work such as underpinning to stabilise the building.  In these instances the whole process could be lengthy and disruptive for the residents and in some instances required temporarily decanting of the occupants to alternative accommodation for the duration of the works.   Most home insurance policies will cover the risk of subsidence and incorporate an excess payment in the region of £1000 (always check the wording of your policy because there can be variations).  This demonstrates that the effects of subsidence can be disruptive and even though it may be covered by home insurance it can still be expensive.

Source: http://www.geoconsult.co.nz/

The above scenario provides an example of what can happen at one end of the scale, however as already stated the vast majority of subsidence claims I managed were dealt with quickly and with minimal disruption, many proving not to be subsidence at all.  When undertaking building surveys, a Surveyor will not just identify where and why subsidence has occurred, but also look for indicators that may contribute to subsidence in the future.  Before providing you with details of what I would look for during a survey (this will be provided in part 2 of the article), I think it is important to first understand exactly what subsidence actually is.

Building design should involved careful consideration of the type/load of the building, the type of foundation used and ground bearing capacity and nature of the ground, the height of the water table and so on.  These types of investigations should help to ensure that once the building is complete and occupied that it does not sink!  Subsidence however is not the same as settlement.  Settlement usually occurs in new or relatively new buildings. As buildings are very heavy they cause the ground to compact, although this will usually stop after a short period of time.  Also, most buildings are constructed in a variety of materials, all of which need to settle and have different rates of shrinkage.  Subsidence occurs when for some reason the load bearing capacity of the ground that a building is placed upon is no longer capable of accommodating that load.  The reasons for the change is the load bearing capacity can occur for many different reasons and many years after the building was first completed.  It is quite feasible for a building to sit quite happily on a piece of ground for many years and due to some of the influences discussed it part 2 of this article, it can start to move.

Cracking in buildings occurs for many different reasons so it is fundamentally important that anyone who undertakes inspections or gives advice in respect of cracking should not make rash judgements and should gather all of the evidence before arriving at a possible cause.  In order to aid the inspector, which as stated previously, can be a Building Surveyor or Structural Engineer, it might be necessary to recommend other investigations such as geo-technical surveys to establish ground type, composition, contaminants etc., trial holes to establish foundation depths, CCTV inspection of the drainage system and possibly an arboricultural survey to give advice on any trees that may be an influencing factor.  The choice of which investigations are needed will be decided once the inspector has made an initial assessment of the cracking.  Therefore when you see cracking in a building it will not always be, in-fact is very rarely likely to be subsidence.  This can only be established through a comprehensive building survey and detailed investigations.

In part 2 of this article (next week) I will discuss subsidence in more detail and provide information in respect of the things a Building Surveyor will look at to identify when and how subsidence is occurring and indicators that may suggest that subsidence can occur in the future.

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