If you’re considering getting your house underpinned, it’s probably because you’ve seen large cracks in external walls or you’ve been told that your property is subsiding. It’s never the news that anyone wants to hear, but underpinning your home is often the answer.

If you deal with the problem as soon as you notice it, it’ll likely cost less. But how much? Let’s go through the costs of underpinning and the things to consider in this guide.

How much does underpinning cost?

How much underpinning costs depends on a variety of factors, including the type of underpinning you have, how large the area is and what kind of access is needed, but the average cost of underpinning a single wall of a semi-detached house is £17,000.

It’s not cheap, but it’s often necessary to ensure that your home is stable and won’t suffer any further damage.

How much does underpinning cost per square metre?

The average cost of underpinning per square metre is around £1,800, with the cheapest type of underpinning averaging at £1,500 per m² and the most expensive £2,600.

What is underpinning?

Underpinning is the process of adding extra support to the foundations of a building to prevent it from sinking into the ground (subsiding). Often, the first sign of a property needing underpinning is cracks in walls, particularly external ones, that travel up a wall in a ‘staircase’ pattern. You may be told that your home needs underpinning by a property surveyor or structural engineer.

You may also need to underpin your home if you’re planning on adding an extension to give your property extra support, or if the neighbours you’re attached to are dealing with subsidence.

What are the 3 types of underpinning?

There are 3 types of underpinning and a structural engineer will generally be able to recommend which one is best for your property:

1. Mass concrete

Mass concrete underpinning involves digging out your property’s foundations and replacing them with concrete. It’s the most common form of underpinning and can be used for both heavy and lighter foundation loads, and for if you need to support your property for a new extension or basement conversion.

A builder will excavate your property’s foundations in sections. They will drive reinforcement bars into the sides of the excavated area, then fill it with concrete and allow it to cure. They’ll then add packing mortar in between the new and old foundation to keep them stable.

2. Beam and base

Beam and base underpinning involves adding a reinforced concrete beam below, above or in replacement of your existing foundations. A builder will excavate the area, fill it with concrete and add the beam where appropriate, to transfer the load of your property to the concrete bases.

3. Mini-piling

Mini-piling involves using high-strength yet small steel casings or threaded bars to stabilise or strengthen your property. A builder will use special rigs to drive steel into the soil or create holes to add the steel reinforcements into. There are 3 types of mini-piling: sectional flight auger (SFA), augered piling and mini bottom-driven piling. A structural engineer or builder will advise you on which type is best.

Mini-piling is the best underpinning method for when you need, or have, deeper foundations. It doesn’t require excavation or concrete, so it often takes less time than mass concrete underpinning.

Underpinning alternative: resin injection

Resin injection is technically an alternative to underpinning. It’s excavation-free, which is why it’s often the cheapest option. Instead of having to dig down to the foundations of your property, a builder will drill precise holes along affected parts of your property, then inject an environmentally-friendly resin into the holes to stabilise your property and prevent further movement.

Resin injection can also be used to fill cracks that your property may have experienced due to subsidence. You should always check with an expert before you have subsidence-related cracks filled.

How long does it take to underpin a house?

How long it takes to underpin a house will depend on the type of underpinning method used, how much of your property needs to be underpinned and whether any issues are discovered once works start. But on average, it’ll take 4-6 weeks to underpin a house.

How long does underpinning last?

It’s impossible to guarantee that underpinning will last forever as foundations could always potentially suffer from soil movement in the future, but when done correctly underpinning should last for hundreds of years.

As long as the project is successful and carried out by a qualified builder, you shouldn’t have to worry about having to underpin your property again in your lifetime – and potentially the next few owners’ lifetimes!

Some people seem to think that you may need to carry out underpinning every 40 years, but there’s no evidence to suggest that this is necessary in a property that has been properly underpinned and is not suffering from ongoing movement.

Can subsidence be fixed without underpinning?

According to some estimates, less than 10% of properties suffering from subsidence need underpinning, and subsidence can be fixed without it. While the most expensive and invasive option, underpinning does give you peace of mind that your foundations have been stabilised. However, other methods can be used to fix subsidence depending on the cause and severity:

• Tree removal: If tree roots have caused your property to subside, removing the tree or adding root barriers to prevent the roots from damaging your foundations can fix it.

• Repairing burst pipes: If you have a water main running under your property and it bursts, it can cause subsidence as the leak washes the soil away underneath your home’s foundations. Repairing or replacing your water supply pipe could stop your property from subsiding further, and stop you from needing to have your home underpinned.

Once you know the cause of subsidence, make sure you speak with a surveyor or structural engineer to confirm whether underpinning should be carried out.

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

Whether you can live in a house while it’s being underpinned depends on how invasive the works are. Most of the time, you’ll be able to live in your home while it’s being underpinned, but always check with the contractor so you have time to arrange alternative accommodation if you need to.

If you’re covered by a good home insurance policy, most insurers will pay for you to live in a hotel or rental property until the work is finished.

Is underpinning covered by insurance?

Providing that you have been truthful when buying your buildings insurance policy and have not suffered from subsidence before (and been told future claims will not be covered), underpinning should be covered by your insurance if you’re having it due to subsidence.

Most home insurance policies will have an excess you need to pay towards any claim, ranging from £100-£1,000. Check your policy to understand how much you’ll have to pay.

If you want to underpin your home to make it more stable for an extension or basement conversion, you’ll have to pay the full cost yourself.

Does underpinning devalue a property?

Underpinning can devalue a property. Some estimates suggest you may lose between 20-25% in value compared to other similar properties in you area. Although underpinning fixes subsidence and in most cases will prevent it from happening again, it can still put some buyers off – and you may find it hard to sell.

The best thing to do is to make sure your home looks fantastic when you come to sell. Make improvements that add value, like building an extension or adding a new kitchen, to make the property look its best.

Remember, as time passes and your property continues to be stable, it will be seen as less of a risk to potential buyers. So if you’re planning on staying in your home for a number of years, you may find that you don’t lose as much value.

Can you insure a house that has been underpinned?

Yes, you can insure a house that has been underpinned, but you may need specialist building insurance. As underpinning suggests that the property has suffered from subsidence, insurers see it as more at risk of suffering from it again.

Many of the most common insurers will not cover a house that has been underpinned, but there are still plenty of providers that will. Be prepared to pay more in premiums, and check the terms of your policy carefully to ensure you’ve got enough cover for your circumstances.

Can I insure a house with subsidence?

It’s almost impossible to insure a house with active subsidence. Before you can insure it you will need to fix the problem causing the subsidence with underpinning, removing or maintaining trees or fixing burst pipes.

Once the subsidence problem has been fixed, you should be able to insure your property with a specialist insurer. Make sure you are completely truthful about the subsidence when you apply for your policy to prevent it from being cancelled or having future claims rejected. You will need to prove that your property is stable and is not suffering from further movement – usually by providing a report from a surveyor or structural engineer.

Is it worth buying a house that needs underpinning?

You should weigh up the pros and cons before buying a house that needs underpinning. As we’ve already mentioned, underpinning can devalue a property, but you may not consider this an issue if you’re planning to live in the house for a long time.

An advantage to buying a property that needs underpinning is that you can probably negotiate a sale at a below-market price. Underpinning can cost a lot of money, and since you won’t be able to insure the property, you will have to pay the full cost yourself. This should be reflected in the price you pay for the house.

Before buying a house that needs underpinning, make sure you get a full structural survey carried out to ensure that there are no other issues with the property.

Underpinning can be difficult to get your head around, so it’s important to speak to a range of specialist builders who can advise and give you a quote. Post your job on HaMuch now and we’ll send it to builders in your area.

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