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Why Is Underpinning Needed and Does It Last?

Why Is Underpinning Needed and Does It Last?

You may have been advised, perhaps by a surveyor or a structural engineer, that your home needs underpinning. This might seem a major step, leaving you wondering if it’s really necessary — and whether, having had it done, you’ll be able to forget about it for the foreseeable future.

Why Is Underpinning Needed?

Essentially, underpinning means using one of various techniques to strengthen or repair the existing foundations of a building, usually   remedy or avoid subsidence. This may be because of:

  • Poor soil quality. If this has a temporary cause, such as faulty drains or tree roots, fixing the cause may be enough. However, if the soil is persistently wet, cracked or liable to shift, it may need underpinning.
  • Excavations below the building. Most common in mining areas, although also found elsewhere, this can cause the soil below the building to collapse.
  • Increase in load. If you’re extending the building, for instance by adding another storey, the foundations may not be adequate for the extra load.
  • Inadequate foundations. Especially in older buildings, the foundations may simply not have been up to the job in the first place, and this could be starting to show.

How Does Underpinning Deal with These Problems?

The most common signs that your home is suffering from subsidence are cracks appearing in the walls, or door and window frames pulling away from the masonry. These are issues that need to be addressed in their own right, but they can also be warning signs that the whole structure is in danger of collapse.

Of the various types of underpinning, there are two main ones. The traditional type, mass concrete underpinning, simply adds in more layers of concrete below the existing foundations. This provides extra support for the weight of the structure.

The alternative, which is becoming more popular, particularly in case of weak soil, is mini piling. Piles of concrete or grout are inserted into the ground below the foundations, through the weak soil and down to a stronger layer. The building’s load is then distributed evenly down through the piles to the stronger soil.

How Long Does Underpinning Last?

U&M provides a ten-year guarantee of its underpinning solutions for defects, but is that as long as you can expect the underpinning to last? And can it fail sooner?

The two main reasons for underpinning to fail are poor installation and new issues arising. The first can be avoided by hiring an expert contractor who guarantees their work, but the second is harder to foresee. For example, if new excavations are made under a building that’s previously been underpinned for weak soil, extra work may be necessary.

In the absence of new issues, however, underpinning is likely to last for the building’s natural life — as long as it’s been expertly installed in the first place. Give us a call to find out more about underpinning your house.