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Commercial Building Subsidence

Is the crack in the masonry a sign of subsidence? And what should you do if it is?

It’s not surprising that subsidence is something that commercial property owners, landlords and tenants fear above most other structural problems.

Not only can subsidence lead to costly damage, but in severe cases, it can also render the building structure unsafe. Therefore, it is crucial that signs of subsidence are promptly investigated by an appropriately qualified building professional, such as an RICS building surveyor or an IStructE structural engineer.

What is Subsidence?

Subsidence is the sinking of an area of ground. If this is below a building, it can lead to structural movement. This movement can manifest in cracking, distortion and even foundation damage and collapse.

Whether your property is a warehouse, school, shop, office or airport, cracking and subsidence is something that should be taken seriously, given the potential for structural instability and harm to occupants and passers by.

Fortunately, in most cases of suspected subsidence, we find no significant movement. And, when subsidence is present, there are usually remedial works that can be done to secure the building, returning it to full functionality.

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Signs of subsidence in commercial buildings

Cracking is the classic sign of subsidence. Progressive cracking, cracks that are wider at the top than the bottom, and cracks that are diagonal in direction, are most likely to indicate subsidence.

Reassuringly, most cracking we find on inspections is not down to subsidence; instead, it’s often a result of thermal expansion and shrinkage. Likewise, we often come across historic movement – this is where the ground has previously settled or moved, but that movement is no longer ongoing and no further damage is anticipated.

Other signs of potential subsidence include:

  • Leaning of walls and other structures
  • Gaps around door- and window-frames
  • Sloping floors
  • Jammed shutters, roller blinds, doors and windows

Causes of subsidence

It is worth being aware of the main causes of subsidence. If these are present, it makes the chances that a crack is down to structural movement more likely.

One of the main origins of ground movement that we come across is faulty or insufficient drainage. Water accumulation softens and erodes the ground below the property, leading to the foundations moving.

A clay-based soil substrate is another common risk factor. Clay soils are prone to drying out during summers and shrinking; this reduction in volume can lead to movement of any structures being supported by the soil. For this reason, we tend to see subsidence more commonly in the South-East of England (where clay soils predominate) than in other areas of the country. Milton Keynes and London are typical areas where structures are at high risk of subsidence.

Trees growing close to buildings can be another cause of subsidence, particularly in clay-soil areas. Large trees can remove substantial amounts of moisture from the soil, again causing shrinkage and posing a subsidence risk. Some species, such as willow and ash, are more problematic than others, because of how thirsty they are.

What to do if you are concerned about subsidence

The first step is normally to instruct an inspection by a chartered surveyor or structural engineer. This could be a specific structural inspection, if subsidence is the only concern, or a full structural survey, if there are other issues you would like investigated.

The surveyor or engineer will carry out a visual inspection of the property, assessing the signs of subsidence and potential causes. This will be a thorough assessment, reporting on all relevant cracks and the risk level associated with them.

Depending on their assessment, several courses of action may be recommended.

In many cases, the cracking is found to be normal movement of a property due to temperature changes and the settling of masonry.

We also often see historic movement, particularly in buildings built in the early 20th century and before. In such cases, some subsidence may have occurred in the past, perhaps due to a clear cause such as a nearby tree or broken drain. If the cause has been fixed, movement has stopped, and the building is still safe and functional, no further action is required, aside from what might be desired for cosmetic reasons.

If subsidence is suspected, but it is not clear and the damage is not severe, a ‘watch and wait’ solution can be proposed. Monitoring the length and width of cracks may be necessary to be certain as to whether there is any ongoing movement.

If ongoing subsidence is identified, whether during an inspection or following monitoring, further intrusive investigations are likely to be recommended. These could include CCTV inspection of the drainage system, trial hole excavations to inspect the foundations, or soil analysis to determine the level of dessication.

Remedial works for subsidence

If the subsidence is severe, the first step will be to make the building safe. Temporary shoring can be used in the short term to stabilise the structure.

Removing the cause of the subsidence is of critical importance. Fixing the cause might include removing nearby trees, replacing rainwater goods and repairing leaking drains.

If the subsidence is relatively minor, sometimes, once the ground has been given chance to return to its natural moisture content, the building can return back to its natural equilibrium, and no further works are needed other than cosmetic fixes.

In other cases, underpinning might be required.

Traditional underpinning uses concrete; more modern methods such as resin injection can also be used to reinstate the structural integrity of the building.

Once all the structural works are complete, cosmetic fixes can begin. This can range from filling small cracks and re-painting internal walls, to repointing, replacing masonry, doors and windows, to partial replacement of wall sections. In rare cases, partial or complete rebuilding may be required.

Subsidence reinstatement

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