Structural Defect Report

Cracking subsidence

Have you become aware of cracking to your property?

We can carry out a defect inspection which includes a detailed analysis of the problem and will explain the cause to you plainly. Where appropriate, details of the remedial work required are included and we can recommend a suitable contractor to carry out the works.

We have considerable experience in the investigation and diagnosis of building defects. These include assessing; cracking to external walls, subsidence and the effect of trees. Our defect reports are often instructed by home owners, business owners and letting agents wanting to obtain independent advice on the defect and to ensure that it is correctly diagnosed. We have also been asked  to report on structural defects when requested by a mortgage lender.

We recommend inspection by a Chartered Surveyor before works are carried out by a builder to ensure that the defect is correctly identified and to prevent ineffective costly works.

What is Subsidence?

This can be defined as the downward movement of the soil beneath a house and involves one or more external factors. For example the action of tree roots on shrinkable soils such as clay, the tree is the external factor. The tree will draw up large amounts of water which will cause the clay to shrink and the house to subside. It is important to differentiate between settlement and subsidence because insurance policies exclude settlement

Another common cause of subsidence are broken drains which cause water to leak out into the clay which over time weakens it significantly. There are more rare instances of subsidence due to coal mining or other mining activity beneath a property however this is less common and usually highlighted as part of a legal review prior to your purchase.

Subsidence cracks are most commonly wider at the top of a property, and the cracks will generally travel diagonally in opposition to the downward movement, this can be seen in the image below.

put simply this means that more than one inspection is required to assess whether movement is continuing. In the case of subsidence it is common to employ a form of monitoring where repeated visits by a special technician show whether movement is continuing or if it has ceased and therefore repair works can be undertaken.

What is Settlement?

Settlement is the consolidation of the subsoil under load. This can also occur if you extend your property and cause additional load to be applied to the soil. In cases of longer term settlement this often involves soft clay subsoil and moisture. Poorly compacted granular materials will experience settlement but the process occurs over a much shorter period of time. Settlement is not necessarily a problem, although it is good practice to leave a vertical movement joint at a junction between a new and an existing structure to overcome settlement of the new structure. A problem occurs where there is differential settlement experienced by connected parts of the same structure which can then lead to cracking developing. Differential settlement can occur where there is variation in foundation pressure on a relatively weak subsoil for example party walls incorporating chimneys in a terrace of Victorian houses have settled more than other less heavily loaded elements of the building. Another causes of differential settlement is unevenly consolidated backfill which can affect foundations and ground bearing floors. The better consolidated areas will settle less that those which are less consolidated.

The key is whether the movement is static and not likely to progress, and if the building is adequately stable, then even substantial settlement may not be problematic.

When attempting to establish the significance of cracking the surveyor should consider the time frame to establish when a cracks have formed and developed. The surveyor will be reliant to some degree on the the recollection of the occupant. The date of internal decorations is the most helpful evidence to demonstrate whether movement has occurred shown as an internal crack. The freshness of external cracking to brickwork will also give a rough indication of the age.

Other common causes of cracking include:

  • Shrinkage of wall material (timber, concrete blockwork).
  • Expansion clay bricks
  • Cavity wall tie failure
  • Thermal movement

Thermal movement

All materials expand and contract as they heat up and cool down. Masonry is weak in tension and as it cools, there is a tendency for cracking to occur if the length of brickwork is too long. To counter this movement it requires movement joints to be incorporated so that thermal movement occurs exactly where you want it to rather than a location that could cause a problem.

Failure of lintel above window or door opening

A common cause of cracking above window and door openings is due to the failure of the lintel (beam over the opening). In this case the cracking appears as a diagonal stepped crack from the upper corner of the openings forming. This can occur because the timber lintel which supports the inner part of the wall has rotten. It can also occur where original timber windows which support the outer part of the wall are replaced with uPVC which can not carry the same load as timber. A further cause involves the dropping of a segmental arch formed in bricking where the arch is too shallow. It is usually relatively easy to remedy this type of failure by strengthening brickwork above the opening with resin bonded stainless steel rods.

If you are in any doubt about cracking to a property, feel free to contact us and one of our expert surveyors will be able to attend your property in the first instance to assess the type of cracking that has occurred.