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What Is Underpinning a House: 2022’s Fundamental Guide

Written by, Marija Petkova

Updated October, 19, 2022

Did you know that there is more than just the foundation under a house?

In fact, several structural elements work together to create a stable base for your home.

If you wonder what is underpinning a house, when is it necessary, and how much it costs, keep reading to find out!

What Is Underpinning a House in the UK?

Underpinning is the process of strengthening and stabilising the foundation of an existing building to prevent it from collapsing in the future.

Typically, owners underpin their house or other properties when the original foundations are no longer strong enough to support the weight of the building or when the ground around the base has changed either through subsidence (land sinking) or water table shifting.

Vendors are required by law to reveal if a property has previously been underpinned, especially if they are flipping houses. Even if they do not, a structural survey should reveal that fact.

How Does Underpinning a House Work?

Underpinning a house is time-consuming, expensive, and challenging work that results in an extended underpinned property longer by several metres and skewered into the ground.

Depending on the extent of the subsidence and structural problems, the process to underpin a house may include one or more of the following approaches:

  • Soil strengthening—the least costly method of underpinning a home is injecting a special resin to replace the soil that has eroded around the property foundation;
  • Mass concrete—pits are dug and filled with concrete below the property’s existing foundation to create another support layer;
  • Beam and base—similar to mass concrete underpinning, but utilises beams to distribute the weight of the foundation by connecting it to a concrete base;
  • Screw piles and brackets—this modern approach uses large screw piles that serve as anchors, which are paired with support brackets to level off the foundation.

Note: The most effective and expensive method is not always necessary, and your construction specialist will be able to advise you on the best course of action for your particular needs.

When Is House Underpinning Necessary?

Underpinning a house is necessary when the existing foundation is in poor condition or the soil becomes unstable and begins sinking (subsidence) due to factors such as:

  • Drought—when the ground becomes too dry, it can’t support the weight of the building;
  • Tree roots—as trees grow and their roots expand, they can put pressure on the foundation and cause it to crack;
  • Leaking pipes—if there is water seeping into the ground around your house, it can make the soil too soft to support the weight of the building;
  • Floods—flooding can damage the foundation and destabilise the ground around your property;
  • Earthquake—an earthquake can shift the ground and damage the base in the process.

Other reasons for needing underpinning include:

  • The addition of new floors or extensions—if you are planning on adding an extension or another floor to your house, you will need to underpin the foundation to support the additional weight;
  • Changes in the water table—if there has been a change in the water table (e.g., due to heavy rains), it can affect the stability of the ground around your house and cause subsidence;
  • The original foundation has greatly deteriorated—older buildings that do not follow modern safety standards must be retrofitted with new construction technologies to ensure they last for a long time.

Underpinning is not always necessary. If the soil sinkage is minor and has been caused by factors like drought, you may be able to correct the problem by watering the ground.

Also, if the cost of underpinning is greater than what it takes to repair or replace the existing foundation, you shouldn’t waste money on underpinning procedures.

How Much Does Underpinning Cost in the UK?

To underpin your house, you would have to pay anywhere between £1,000 to £20,000 as the prices vary depending on the property’s size and condition, as well as the type of underpinning required. 

Moreover, there may be additional and unsuspected costs for services like replacing bricks and timbers damaged by subsidence, as well as interior decoration expenses to repair wall, windows, doors, and floor damage.

Note: If you have recently purchased an underpinned house with hidden flaws, or it has been damaged due to the lack of underpinning, your seller may be liable for the damages you may have incurred.

Can You Get an Underpinned House Insurance?

In most cases, house underpinning is not covered by standard home insurance policies, as it is considered to be a preventative measure rather than a repair.

However, you can obtain a specialist home underpinning insurance in the UK that covers the costs to underpin your house and mend any damages it has sustained.

Note: If you plan on extending your property or want to make some structural modifications unrelated to underpinning, then this kind of work won’t be covered by your insurance.

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While costly, underpinning your property is crucial to repairing existing damage to your house and its foundation or preventing future destruction caused by anything from subsidence to house extensions. That way, you’ll keep your home safe and sound for years to come.

Frequently Asked Questions And Their Answers

Does underpinning devalue a property?

Depending on the degree of the subsidence and the damages it has caused, a property that has been underpinned might be worth 20% to 25% less.

How much does underpinning cost?

The cost to underpin your house varies between £1,000 and £20,000 depending on factors such as the size of your property and the type of underpinning you require.

Should I buy an underpinned house?

If you’re buying an underpinned house, there shouldn’t be any problems with your mortgage or your insurance as long as the property’s structure shows no further issues.

What is underpinning a house?

House underpinning is a construction technique used to strengthen the foundation of a house or add another foundation layer below the existing one.

My name is Marija, and I'm a financial writer at DontDisappointMe. Although finance might not be everyone's cup of tea, my 10+ years of working in one of the biggest banks in my country, and my interest in extensive research on everything finance/investment-related, have made me somewhat of an expert in the field (if I do say so myself). No longer having the passion to work in a corporate setting, I decided that I couldn't let all of this knowledge go to waste so I started writing. And, here I am! Today I try to share my knowledge with my audience in the hopes of making this topic as simple and interesting as possible. In my leisure time, I like spending time with my family and travelling to new locations.