A Beginner’s Guide to Spotting Subsidence

20 Feb 2018

by Helen Thring

Subsidence is the movement of your home’s structural fabric. Most houses have their load bearing walls built on strips of concrete foundations. Known as strip foundations, they are poured into trenches and are laid on undisturbed subsoil. Once set, the walls and any external brick skin are laid onto the strip foundation and the trench is then backfilled. Sometimes, when ground conditions demand, reinforced concrete slabs or ‘rafts’ are laid and the house effectively ‘floats’ on this raft.

Subsidence occurs when the house and its foundations are somehow undermined. In some cases, older properties were built onto the subsoil, without any concrete foundation. Over time, ground conditions might vary, causing subsidence or ground heave to present itself. The most likely causes of subsidence include;

• Historic mining works in the immediate area

• Heavy construction work very close by or under the property

• Leaking drains or watercourses that wash away subsoils and undermine the foundations

• Tree roots or vegetation (e.g. Japanese knotweed)

• Overloading of foundations during repair or extension / renovation

Cracks from subsidence can appear and spread rapidly compared to regular cracks. They usually Present both inside and outside the property and may look narrower at one end. They usually run diagonally across the wall and can be found around doors and windows.

If you suspect a home might be suffering from subsidence, consider commissioning a building survey. If your building insurance covers subsidence, consider making a claim through your insurer. However, once a property has been the subject of a claim, it’s worth noting that future insurance premiums are likely to be affected.

Subsidence and the causes of it can usually be rectified fairly easily, with underpinning being the most usual remedy. This involves laying a more substantial foundation of concrete under the affected area. This can be expensive, but in many cases your house building insurance will cover it, perhaps subject to an excess payment of say £1,000.

Where a property has previously suffered from subsidence its marketability and value may be adversely affected. Furthermore, hiding the fact from potential purchasers if they ask will almost certainly be a serious matter resulting in contractual penalties.