A guide to underpinning

If you’re buying or selling a house and have come across the word ‘underpinning’, you may be wondering what it means and how it could affect the property. Essentially, underpinning a house is the process of reinforcing, repairing and/or increasing the depth of its foundations. This sounds serious and it certainly can be. It could affect your desire to buy a property or your ability to sell, so let’s find out more…

What does underpinning mean?

If the foundations of a property have moved either because of changes to the ground conditions e.g., subsidence, action may need to be taken to safeguard the structural integrity. Equally, if a storey is added to a property (for example, a loft conversion), the depth of the existing foundations may be insufficient to support the increased loading and work may be needed to address this.

Underpinning a house is when work is done to reinforce, repair or increase the depth of the foundations, ensuring they are adequate to support the building above. There are several different methods of underpinning appropriate for different situations:

1. Soil strengthening

Often the cheapest option, soil strengthening is when resin is injected into the ground, replacing any soil that’s eroded or moved.

2. Mass concrete

Pits are dug underneath the existing foundations and filled with concrete. This essentially creates an increased thickness of foundations.

3. Beam and base

Concrete beams are placed underneath the existing foundations, distributing the building’s weight across concrete bases.

4. Screw piles and brackets

Screw piles are drilled deep into the ground as anchors then supporting brackets are attached beneath the existing foundations.

How to identify unstable foundations

As you may imagine, when the foundations of a property are compromised, the building itself no longer has a stable base and could move. While this conjures dramatic images of houses leaning at a visible angle, the signs on unstable foundations and the need for underpinning are often more subtle, such as:

  • Inconsistent width cracks in walls and ceilings
  • Cracks/gaps around windows and door frames
  • Windows or doors that no longer fit in their frames properly
  • Sloping floors

When does a property require underpinning?

Even if you spot the signs of structural movement  listed above, it’s not yet time to panic. They can also be symptoms relating to far less serious issues which won’t require underpinning.

Underpinning for subsidence is usually only needed when ground instability is ongoing or progressive. The best course of action is to commission a survey to identify the cause of any cracks, gaps or slopes you’ve noticed.

You may also need to consider underpinning if there has been a natural event e.g. landslip, or if you are considering adding floors to a building.

Does underpinning a house require planning permission?

In many cases planning permission would not normally be required for underpinning unless the property is Listed or in a designated area.  We recommend you check with your local planning authority before contemplating this type of work.

All underpinning work would require specialist design by a Structural Engineer, and the works should be carried out under a formal Building Regulations approval process.

How much does underpinning cost?

The cost of underpinning varies depending on exactly what needs doing , relevant to the specifics of the property, local ground conditions, the extent and type of underpinning work required etc. It is therefore difficult to provide accurate cost guidance.

What should you consider when selling an underpinned property?

  1. There’s no sense in trying to conceal that the property is underpinned: the buyer’s structural surveyor will find out anyway. Be totally honest with the estate agent and any prospective buyers to save wasted time in the long run.
  2. It is a nice gesture to share the name of your house insurance provider with prospective buyers so that they a) know the house is insurable and b) know where to go for insurance.
  3. Keep in mind that, even though the house is underpinned, providing that the works has been carried out properly (following a Structural Engineer’s design and subject to a grant of Building Regulations approval), it shouldn’t affect the value of the property.
  4. If the underpinning work was carried out under an insurance claim, copies of the documentation including plans, specifications and approval documentation will be invaluable to your buyer’s surveyor when carrying out their assessment of the property.

What should you consider when buying an underpinned property?

  1. Definitely get a full building survey completed to fully understand the property and learn about any further structural problems.
  2. The works have been properly designed and supervised, and signed off under Building Regulations to ensure that getting a mortgage is not a problem (assuming there are no additional issues revealed in the building survey).
  3. You may need to get specialist insurance and this may require you to pay a higher premium.

Get in touch

Whether you’re selling or buying an underpinned property, we’re here to help. As RICS Regulated Chartered Surveyors, we are qualified and experienced in surveying all kinds of properties, including those with underpinning. We can help determine whether a house has further structural issues and put your mind at rest that it’s concealing no nasty secrets!

If you’d like to book a survey or ask any questions, please get in touch.