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    What is Underpinning? An Essential Guide

    By The reallymoving Team Updated 24th May, 2024

    Reviewed by Em Smith

    What is underpinning and what should you do if you suspect a property has been underpinned? Our guide will help you find out.

    What is Underpinning? An Essential Guide

    What is underpinning a house?

    Underpinning is a technique used to strengthen the foundation of an unsecure building. It’s usually used when a house is suffering from current or previous subsidence, often due to soil conditions.

    When is underpinning needed?

    Normally, underpinning is required when the structure of a property moves (subsidence), and the foundations need to be repaired.

    The soil beneath the existing foundation is excavated and replaced with new materials to repair the structure of the property.

    Does my house need underpinning?

    Subsidence occurs when the supporting soil within the foundation moves away from the structure, taking away its support. This causes the structure to move, and although there are many reasons for why this happens, many are a result of either physical problems with the property itself or issues with the ground and the foundations.

    Why do foundations fail?

    Some of the reasons the foundations of a house might fail include:
    • Erosion

    • Problems with the building materials

    • Foundation design issues

    • Poor soil

    • Drainage issues

    Signs your house might need underpinning

    You won’t always notice a huge hole appear in the ground before realising your house needs to be underpinned. You may, however, notice smaller signs such as cracks in the walls and more severe cracks around windows and doorframes.

    In extreme cases, you’ll notice the property leaning to one side. In all cases you’ll need to have a Building Survey (also known as a Structural Survey) carried out to discover the extent of the damage and to reveal any other issues with the property.

    If you’re worried your property might be suffering from subsidence, find out more information in our guide: what to do if you think your property has subsidence.

    What to do if you think your property has been, or needs to be, underpinned

    The first and most important step is to speak to your Chartered Surveyor and have your property inspected by a Structural Engineer.

    The report will be able to identify any structural issues which will then determine if your property needs to be underpinned or has previously been underpinned.

    For properties that are structurally unsafe and in need of underpinning, the best way forward is to seek professional advice and expertise.

    Methods of underpinning

    There are a few common methods to underpinning a property, but if it's not carried out properly, it can lead to serious damage or even the collapse of the existing structure.

    Mass concrete underpinning

    Also known as the pit method, mass concrete underpinning is the most traditional method of underpinning. This involves excavating the ground below the existing foundation in controlled segments to the depth of stable soil of suitable bearing capacity.

    Beam and base underpinning

    Beam and base underpinning is a more advanced adaptation of mass concrete underpinning. It uses a reinforced concrete beam above, below, or to replace the foundation footing. The beams transfer the load of the building to reinforced concrete bases.  

    Mini-piled underpinning

    This method screws hollow steel piles down below existing foundations. The space within the steel frame is then filled with either concrete or grout. The soil is given support from these external steel casing and can be useful in situations with poor quality soil.

    This method is also good for areas with limited access as the equipment can be smaller in comparison to other methods. However, this is a more precise method and therefore can be more expensive than other methods.

    Hire an expert with experience in subsidence and look for companies that specialise in it, that way they can tell you which type of underpinning is most appropriate.

    How much does underpinning a house cost?

    Once you know the extent of the damage, you’ll be able to get a quote from underpinning companies.

    All costs depend on how much work needs to be done, and the type of underpinning you will need. There are many other variables to take into account too, such as the location of your property.

    If it’s hard to get to or access to the site is restricted, then the construction work will take a lot longer and it will be a more difficult job, which can make the work cost more.

    Although underpinning is often an unwanted expense, if left unresolved the cost could be much higher, putting your entire property at risk.

    For the sake of making your property structurally secure and safe to live in, the cost of underpinning is often worth it in the long run.

    Can you insure a house that has been underpinned?

    You can usually insure a house that has been underpinned. But you may struggle to get standard home insurance, and it will probably be more expensive.

    Insuring a house that has been underpinned can be more difficult as it means that the property is at risk of subsidence.

    Will underpinning provide a permanent solution?

    While underpinning a house will fix the problem in the short term, the risk of subsidence won’t go away completely.

    This means that even if your house was underpinned years ago, you could still have difficulty getting standard home insurance, especially if the house is still on clay soil.

    However, many specialist insurance providers can provide a competitive quote based on the property’s history and circumstance. So, while it might be more expensive, you should be able to protect your home with suitable cover.

    Should I buy a house that has been underpinned?

    You should think carefully before buying a house that has been underpinned as there are risks involved. However, that doesn’t necessarily mean that you shouldn’t buy a house that has been underpinned.

    If you’re considering buying a house that has been underpinned, you should find out whether there are any ongoing problems affecting the property. You can find this out by getting a full structural survey.

    Even if the property is in good condition, you should keep in mind that some people will be put off buying a house that has been underpinned.

    This isn’t to say that it’s impossible – after all, you’re thinking about buying an underpinned house. But you should factor into your decision the possibility that it could be more difficult to sell in the future.

    Underpinning is a complicated process, and one that costs a lot of time and money. Before you try to fix the problem, be sure to seek professional guidance every step of the way to be certain you’re in good hands.
    For more information on subsidence and safely securing your home, read more on how surveyors spot underpinning.

    Underpinning FAQs

    What is the difference between underpinning and foundation?

    Underpinning is used to reinforce or repair existing foundations in the case of subsidence.

    Foundations are the original lower structures used to distribute the weight of a building.

    Can you live in a house that needs underpinning?

    It will depend on the extent of the work needed if you will be able to live in the house during the underpinning process. However, if the property needs underpinning but this process has not begun it is not safe to live in a property with subsidence and these properties will likely be ‘unmortgageable’.

    Do cracks always mean subsidence? 

    Not all cracks in walls mean subsidence. Smaller, superficial cracks can often be fixed with painting and redecorating. However, larger cracks can point towards issues with the foundations of the house and should be investigated by professionals.

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