Underpinning: The Complete Guide [Top 11 Most Popular Questions]

If you’ve been unfortunate enough to have your property diagnosed with subsidence, underpinning may have been suggested as the solution.

So, what is underpinning?

Underpinning is a construction method used to strengthen and stabilise the foundations of a building. A house may need to be underpinned if it is affected by subsidence. Underpinning can affect how easy (and cheap) it is to get buildings insurance for your home. It can also make a property harder to sell.

Our complete guide answers the top 11 most popular questions homeowners, sellers and buyers have on underpinned houses.

If you want to find out how much underpinning devalues a property, how much it costs and how common it is, you’ve come to the right place.

Read on to find out the answers to these questions and more.

1. What is underpinning a house?

Underpinning is a construction method used to strengthen and stabilise the foundations of a building.

A house may need to be underpinned if it has been affected by subsidence.

Subsidence occurs when the ground beneath a property begins to sink downwards. When the foundations of a property are no longer supported by the ground beneath, walls and floors can shift and crack.

Subsidence puts your home at serious risk of structural problems if left untreated.

Underpinning is the most invasive, expensive, and time-consuming treatment for subsidence. It is often recommended as a “last resort”.

The underpinning process is designed to reinforce the foundations of a house. This is achieved either by:

• excavating any soil beneath the house that no longer supports the structure and replacing it with stronger materials; or
• inserting deeper footings into firmer ground beneath the property.

A variety of different methods and materials are used to underpin houses. Some are more disruptive than others. The method that is right for you will depend on several factors, including the ground conditions.

Let’s take a look at some of the different types of underpinning…

2. What are the different types of underpinning?

There are quite a few different types of underpinning methods. The three most common methods are:

• Mass concrete underpinning. This is the traditional method, where sections are excavated beneath the foundations of your home one at a time. The sections are then filled with concrete. This tends to be a long, disruptive process but can be effective for shallow foundations.
• Beam and base method. A reinforced concrete beam is constructed below, above or in replacement of the existing foundation. The beam then transfers the load of your house to mass concrete bases, which are constructed at designed strategic locations.
• Mini-pile method. “Piles” (metal or concrete shafts) are inserted into the ground through the weaker soil to a level of bedrock or firmer soil that can support the weight of your home more efficiently. This method involves no excavation, and so is the least disruptive of the three methods.

The choice of method appropriate for your case will largely depend on the ground conditions and the required foundation depth. Your structural engineer will be able to recommend and design the treatment plan that’s right for you.

3. How common is underpinning?

The Royal Institution of Chartered Surveyors (RICS) estimate that less than 10% of properties suffering from subsidence need to be underpinned. Underpinning is only ever used as a last resort in the worst-case scenarios. Most of the time, subsidence can be repaired without the need for underpinning.

There will be some areas that have a higher concentration of underpinned properties. This is because certain areas, such as the South East of England, are more prone to subsidence movement than the rest of the UK.

4. How do you know if a house needs underpinning?

There are two main reasons why a house will need to be underpinned:

1. Subsidence. If the existing foundations of your house have moved because of subsidence, then it may need to be underpinned. Underpinning is only ever recommended as a last resort. Make sure to explore the other ways to fix subsidence first.
2. You want to add another storey to your home. You may also need to underpin your property if you are looking to add extra floors to your home. Underpinning will be necessary if the depth of the existing foundations isn’t enough to support the modified property or its weight.

The following signs can indicate that your house has subsidence and may need to be underpinned:

• Large cracks in walls
• Doors and windows sticking and/or becoming misaligned
• Sinking and/or sloping floors
• Wallpaper creasing or rippling at joins with no signs of damp
• Extension cracking or moving away from main property
• Noticeable leaning of a house

The only way you’ll know for certain whether a house needs underpinning is to get a structural engineer to visit your property and carry out an inspection.

5. Do you need building regulations approval for underpinning?

Building regulations approval is required if you need to underpin all or part of the foundations of your house. Building regulation approval makes sure the work you’re doing reaches certain safety standards. If underpinning is not carried out correctly, it can result in serious structural problems, or even the collapse of your home.

You can speak with your Local Authority’s Building Control department for advice on how to apply for building regulations approval.

The Local Council Building Control Officer will come to inspect the work at various stages to ensure it meets the building regulations standards. They will issue you with a “Formal Completion Certificate” once they have signed off the works.

6. How much does it cost to underpin your house?

Underpinning can cost anywhere between £6,000 and £50,000, depending on the size of your property and the extent of the damage. The treatment method and length of time taken to complete the work will also affect the cost. Most insurers will cover the cost, leaving you with just a subsidence excess to pay of around £1,000.

Related: "Quick Overview: Is Subsidence Going To Be Expensive To Fix?"

A good home insurance policy should cover you for alternative accommodation when the remedial works are being carried out, if it means the property is uninhabitable. However, not all will, so remember to factor in these costs (if needed) as they’re often overlooked.

Related: Read my articles on "Subsidence & Insurance: FAQs, Common Exclusions & Top Tips"

7. Can you live in a house while it is being underpinned?

Whether you can live in a house while it is being underpinned will depend on how extensive and invasive the works are. A good home insurance policy should cover you for alternative accommodation when the remedial works are being carried out, if it means the property is uninhabitable.

8. Is it hard to sell a house that has been underpinned?

Selling an underpinned house can be tricky. If the underpinning has resolved any structural issues, you should (in theory) be able to sell the property like any other. However, many people are wary of buying an underpinned property. This means it can take a lot longer to find a buyer.

Buyers can be put off for several reasons including the associated stigma, increased insurance premiums and future saleability of the property.

The condition of the property, the market conditions, and the level of competition will also affect how hard it is to sell.

It’s important to note that while these factors can make it harder to sell an underpinned property, they do not necessarily mean that it’s impossible. A well-presented, well-maintained property with no signs of further ground movement can still be attractive to potential buyers.

Related: We cover the best ways to sell an underpinned house based on your priorities in our article, "Can I Sell an Underpinned House? [2 Best Ways to Sell & My Top Tips]".

If you're struggling to sell a house that's been underpinned or has a history of subsidence, try out the free online quiz I've created for you:

9. Does underpinning devalue a house?

In theory, an underpinned house should be worth its original, pre-subsidence value because the problem has been fixed. But in reality, lots of buyers are scared to purchase an underpinned property and it will affect price you’ll get. In my experience, underpinning devalues a house by around 5%.

If a house has been underpinned to a high standard, it will restore its value in the eyes of lenders and insurers. The property is structurally sound and therefore mortgageable and insurable (albeit with higher premiums).

However, buyers are more likely to focus on the stigma and perceived risks associated with underpinned properties. This means you may struggle to achieve the property’s original, pre-subsidence value when you go to sell.

9.1 How much does underpinning devalue a property?

I think it’s important to dispel the myth that underpinning devalues a house by 20-25% on average. To do this, we need to recognise the distinction between ongoing and historic subsidence.

In my experience, a property with ongoing subsidence can be devalued by around 20-25%.

BUT, if the property has been underpinned and the work has been carried out to a high standard, approved, and certified, the house is now:

• Structurally sound
• Mortgageable
• Insurable (albeit with higher premiums)

In my experience, underpinning devalues a property by 5% on average. The actual figure will depend a lot on the demand, location, and desirability of the property.

Another factor that might affect the value of an underpinned house is time. If the underpinning was carried out more recently, this might influence the price buyers are willing to offer.

Buyers might be more hesitant to offer the full asking price if the property is still being monitored post-repairs. The perceived risk of subsidence reoccurring might be higher as there is no track record to prove the underpinning has fixed the issue (even if there are certificates to show otherwise).

Insurance premiums and the subsidence excess (if subsidence cover is offered) are also likely to be higher if the underpinning has been carried out recently. Buyers therefore might try to negotiate on price a little to factor in the additional insurance expenses.

10. Is it ok to buy a house that has been underpinned?

You do not need to walk away from your dream home if you discover it has been underpinned. After all, a house that has been underpinned can be more structurally sound than one that hasn’t! However, there are some things you should consider before you sign on the dotted line.

Here are some of my tips that will help you gather all the information you need to make an informed decision:

1. Get a structural engineer to carry out a full structural survey. It’s important to find out if the house is structurally sound, especially when it’s had a history of subsidence. The structural engineer will be able to tell you if there have been any signs of recent ground movement.
2. Ask the seller for the relevant certificates. Make sure to ask the seller for the Certificate of Structural Adequacy and the Formal Completion Certificate. Each certificate confirms that the underpinning has been inspected and approved by a structural engineer and building control officer respectively.
3. Look in detail at home insurance policies. Your choice of insurers will be limited (especially if the underpinning was recent). Not all insurance companies are happy to provide quotes for homes that have been underpinned. If the underpinning was recent, you can expect to pay higher insurance premiums and subsidence excess.
4. Consult with your mortgage lender. Make sure that your mortgage lender is aware the property has been underpinned because it suffered from historic subsidence. They may want you to provide in-depth information about the repairs, timelines and any supporting documents provided by the seller.
5. Consider how hard it is going to be to sell in the future. You should consider how easy it will be to sell an underpinned house in the future. It can be much harder and take a lot longer than selling a “problem-free” property.

Top tip: Be sure to check your insurance policy wording. Some insurers will exclude future subsidence claims from the policy if the property has been underpinned. Others may increase the subsidence excess amount.

I spoke with a reader who owned a property with a history of subsidence and had a £10,000 subsidence excess if they claimed on their insurance!

If you are considering buying a previously underpinned property (PUP), make sure you have considered the above points. The most important thing to establish will be that the house is structurally sound, and the underpinning was carried out under building regulation approved standards.

11. How to tell if a house has been underpinned?

It can be difficult to tell if a property has been underpinned just by looking at it. Any underpinning work will be concealed below ground and so won’t be picked up during a typical survey inspection. The best way to tell if a house has been underpinned is to get a structural engineer to carry out an invasive inspection.

Before you start searching “structural engineers near me”, there are other (less expensive) ways that might uncover if your house, or a house you’re considering buying, has been underpinned:

1. Speak to the seller. Sellers should disclose if a house has been underpinned if they are asked about it. If you suspect the property may have been underpinned, ask your solicitor to raise this as an enquiry with the seller. They should be able to provide you with a Certificate of Structural Adequacy and Formal Completion Certificate. These certificates confirm the property is now structurally sound and remedial works have been signed off.
2. Contact your Local Authority. Your Local Authority’s Building Control Department should have records of any underpinning work done at the property. This is because building regulations approval is required for underpinning.
3. Contact your insurance provider. If the underpinning was carried out under an insurance claim, they may have records of this on their claims database.

If you are still none the wiser, it’s worth getting a structural engineer over to carry out an invasive inspection.

It is important to know 1. if your house has been underpinned and 2. that the works have been signed off by the necessary parties. If not, it can have a knock-on effect when you come to sell your property in the future.

Related: "Help! 6 Reasons Why It Is Hard to Sell a House That Has Been Underpinned".