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What is Subsidence?

Zenyx Griffiths

Written by Reviewed by Mike Ashton

29th Oct 2020 (Last updated on 30th Nov 2020) 9 minute read

What is Subsidence?

Subsidence is when the ground beneath your property compresses or sinks, creating an unbalanced foundation. As the ground becomes unstable, the foundations become misaligned, affecting the property’s structural safety and often its overall value.

Subsidence is a dreaded word for many homeowners and can be a serious issue. However, unless you’ve experienced it on a previous property, you may not be aware of its meaning or what to do if your house starts to show signs. If you suspect your property is suffering from subsidence, it would be wise to find a surveyor to conduct a property survey and asses any structural damage that might be occurring.

To help you learn more about subsidence, we’ve created this guide to discuss what the term means, how it affects your property and what to do next. Step by step, we’ll take you through the process so that you’re fully aware of what to do once you’ve determined that subsidence is the issue you're dealing with.

What is Subsidence?

In simple terms, properties that are subsiding are sinking into the ground. As the ground moves lower and becomes unstable, so do the foundations of the property as the weight can no longer be supported. It‘s especially concerning if the ground underneath is sinking at different rates, creating an unbalanced structure.

It’s important to state that subsidence is not the same as heave. Heave is where parts of the ground beneath your home shift upwards and pushes the foundation higher. Subsidence is also not the same as a landslide or landslip, where the ground under your home is washed away or moves down a slope taking the property with it.

What Causes Subsidence?

There are a variety of issues that can cause subsidence, including both natural and man-made problems. Not all homes are at equal risk of subsidence but it’s important to be aware of the factors that could encourage it:

  • Weather - during wet weather, the ground will expand from the moisture but then contract during warmer months. This process of shrinking and swelling can create an unstable ground.
  • Clay soil - clay soil can shrink, crack and even shift during hot weather. This creates an unstable ground, pulling the foundations as it shrinks from the dry, hot weather.
  • Droughts - if your area is prone to droughts, you’re more likely to experience subsidence as the soil dries out quickly.
  • Tree roots - trees and shrubs can be a major factor if they're situated close to the property’s foundations. Some species, like willows and elm trees, absorb water much more quickly, drying out the soil. Tree roots removing moisture from the soil is one of the most common reasons for subsidence. There are a variety of plants that can damage your property and potentially cause subsidence.
  • Shallow foundations - this is particularly common in older properties. However, older homes also tend to be built from bricks and lime mortar which can sometimes make them more flexible and less likely to be damaged by subsidence.
  • Previously mined areas - previous and current mining activity can be a major risk factor. Former quarry or pit sites can cause instability as the materials decompose. 
  • Leaking drains - a leaking drain can wash away or soften the soil underneath your property making it unstable and more likely to collapse.

Evidence of Subsidence in a House

If you think your house could be suffering from subsidence, then it’s important to hire a chartered surveyor to asses its foundation and conduct a property survey to determine whether or not this is the cause of any structural damage.

Although hiring a chartered surveyor will help professionally determine if subsidence is the issue, there are a few signs that can warn you in advance. Many homes have a few cracks from the property settling, but the cracks that appear from subsidence are quite distinctive making them easier to spot.

Cracks from subsidence are likely to:

  • Be wider than 3mm (or a 10p coin)
  • Appear both inside and outside the property
  • Be found around doors and windows
  • Run diagonally and look more narrow at one end

Cracks, however, aren’t the only sign of subsidence. If the doors or windows often jam or stick when you’re trying to open and close them, it could be a sign that they’re warped and out of alignment. If any wallpaper in the house is crinkling at the wall and ceiling joint, then this could also be a sign of subsidence if damp is ruled out as being the source. If there are cracks where an extension joins the property, then you could be dealing with subsidence.

It’s important to examine these signs carefully before assuming the worst, not all cracks are from subsidence. Always seek professional advice if you suspect your property is subsiding. The sooner it’s discovered and diagnosed, the easier it can be to rectify. Seek the support of a surveyor if you believe your property, or the property you’re considering buying, is suffering from subsidence.

How to Prevent the Risk of Subsidence

Now that you’re aware of the signs and causes of subsidence, you can take the appropriate steps to try to reduce the risk of it occurring. To help prevent the risk of subsidence, you can:

  • Remove any trees or shrubs that are too close to your property (ask a tree surgeon for advice on how to safely remove these)
  • Regularly prune any trees that are close to your property but within a safe distance - do not plant any trees within 10 metres of your home, 40 metres for larger trees
  • Avoid leaks by maintaining any external guttering, pipes or plumbing
  • Try to catch excess water to avoid the soil from becoming waterlogged - water butts can be used to collect rainfall

What to do if You Suspect Your House is Subsiding

If you detect signs of subsidence, you should seek expert advice and contact your insurer immediately. Subsidence is a serious issue, but there’s no need to panic as it can often be fixed, especially if it's caught early enough. The first thing you should do if you notice these signs is to check if your insurance covers subsidence. Your insurer can then help you decide on the best course of action.

The most common first step is to hire a reliable, RICS accredited surveyor to conduct a property survey and asses your home. There are a variety of survey types available but the one most suited to detecting subsidence is the building survey as it’s the most thorough and includes the inspection of the building’s structure. Basic signs may be discovered in a homebuyers survey, but a full structural survey is recommended to receive a more definitive answer. A structural survey is especially recommended if you are buying a house in a former or current mining area.

If the damage is minor, the cause easily detected and your home has stopped moving, then repairs will most likely begin straight away. If the damage is more severe, then the surveyor may decide to monitor your home before declaring whether or not the ground is sinking. This can take up to 12 months where a long-term solution needs to be decided.  

How to Treat Subsidence

If, after monitoring the property’s structure, the cause determined is minor, then it should be easily fixed. Only an expert can provide you with the most suitable course of action, but for minor issues, this could be:

  • Removing any obstructing trees or vegetation
  • Repairing damaged drains or pipes
  • Demolishing and rebuilding garages or extensions that have caused the instability

However, if the damage is more severe or obvious, you may need more structural support through a process called underpinning. To ensure that this is the process needed to fix the subsidence, the foundations will first be investigated and soil samples will be taken.

Underpinning is a construction method used to help strengthen foundations. The soil beneath the property is excavated and replaced with the appropriate materials needed to repair the structure, usually concrete. It’s often an expensive and invasive method, but according to the Royal Institution of Chartered Surveyors (RICS), less than 10% of properties affected by subsidence need underpinning as it’s often used as a last resort.

No matter what course of action you’re recommended to take, you must always hire and consult with experienced workers to conduct the repairs. Trying to solve the issue yourself or hiring someone underqualified or inexperienced, could only make the damage worse and ultimately cost you more.

Selling a House with Subsidence

The reality is that many properties with a history of subsidence don’t usually sell quickly due to the potential risk of the issue reoccurring, and complications that can arise with obtaining building insurance. If you’re selling a property with a history of subsidence, you cannot conceal this information from any prospective buyers. Subsidence is a term that can sometimes be a deterrent, but you cannot hide the issue. To help encourage potential buyers, you’ll need to satisfy them that you’ve dealt with the problem as accurately and professionally as possible.

Treating and solving the issue is the best course of action. If the property has existing subsidence issues, then it’ll be very difficult to sell as you can only accept cash offers as most mortgage lenders will not lend on properties with existing subsidence issues.

Ensure you keep all documents concerning the repairs as proof that it has been accurately dealt with, reducing the risk of reoccurring subsidence. Present potential buyers with your survey report and don’t panic if they ask to conduct their own as it’s all part of the process. Encourage them that the work was completed by professionals and that any structural work abides by building regulations.

The best strategy for selling a house with a history of subsidence would be to be completely open and honest, answering any questions the potential buyer may have about the repairs done and the risk of it reoccurring.

Buying a House with Subsidence

When viewing properties, ask the seller and estate agent if the property has a history of suffering from subsidence. If you suspect that the house has signs of subsidence, then get a full structural survey to inform you of any possible risks. This type of survey is the most thorough and comprehensive and will require a more in-depth assessment of the property, unlike a simple valuation inspection. 

If the seller believes that the repairs for the subsidence have taken place, then your conveyancing solicitor should uncover the legal documents to verify this. You must find out if the work completed was to the standards set by the Building Research Establishment.

If you’re considering purchasing a house with a history of subsidence, you’ll want to find out who the property is currently insured by and for how much. You should compare different insurance quotes as the choices can be limited. You will have to disclose to the insurance provider that the property has or has previously had subsidence. This could result in higher costs and not all providers will cover it.

What is Subsidence Excess?

Subsidence excess is the amount you have to pay when making a claim for subsidence with your insurance provider. It’s usually a one-off payment but it can increase depending on whether there was damage caused and how significant it was. The payment required varies greatly and can rise if your property has been previously affected by the issue.

Not all insurance providers cover damage by subsidence so it’s vital to check beforehand. If you suspect your home is showing signs of potential subsidence damage, it’s important to contact your insurance provider immediately to discuss your options.

Save on Your Surveying with Compare My Move

If you suspect your property is at risk of suffering from subsidence, then hiring a reliable surveyor to conduct a full structural survey should be your next move. To save you both time and money, fill out our quick and simple form to get connected with up to 5 highly dependable property surveyors in your area.

Zenyx Griffiths

Before Compare My Move, Zenyx once wrote lifestyle and entertainment articles for the online magazine, Society19 as well as news articles for Ffotogallery.

Mike Ashton

Reviewed by Mike Ashton

Director at Cambridge Building Surveyors, Cambridge Building Surveyors

With over 20 years of experience in the property surveying industry, Mike Ashton is now the director at Cambridge Building Surveyors.

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