Subsidence is a word that strikes fear into the minds of homeowners and homebuyers alike.
In the worst cases, it can cost tens of thousands of pounds to remedy and can result in significantly lower selling prices. It can also make a home much harder to sell.
It's not always the case though.
But what is subsidence, what causes the it, and what can be done about it?
Does subsidence make a home completely unsellable, or are there still ways of selling a home with subsidence?
In this guide we will take a detailed look at subsidence and assess your options. If you're looking to sell your property, check out our other article about selling a house with subsidence.
1. What is subsidence?
Subsidence is a structural problem caused by the foundations of a house sinking into the subsoil. This can be caused by water leaks, drought, tree roots, mining and other causes.
This can cause cracks in the walls, put doors and windows out of alignment, and ultimately compromise the structural integrity of the building.
All new buildings will settle a little in the first few years, but subsidence occurs when different parts of a property sink at different rates.
- Subsidence can usually be fixed, but can be very expensive.
- If left alone, subsidence can cause structural weakness and even the collapse of buildings.
- Subsidence occurs when the ground your property is built on sinks, causing the foundations of your property to drop (a.k.a. “subside”) into the space.
- Subsidence is at its worst when different parts of the property are dropping at different rates. This causes “shearing” forces between different parts of the structure and can significantly destabilise the property.
There's a difference between "historic" and "active" movement though.
1.1. Historic movement vs Active movement
Subsidence falls into two main categories:
- Historic movement – which has caused problems in the past but has since stopped, or been repaired
- Active movement – which is still causing problems now and will continue to do so
Historic subsidence is usually less of a problem (although it can still affect your home sale), but active subsidence will cause problems and inevitably reduce your sale price.
1.2. Settlement, heave and landslip
There are several other reasons a property could move. These are subtly different from subsidence, but can still cause similar problems with your property:
- Settlement (pressing down)
- Heave (rising up)
- Landslip (moving sideways)
We'll cover each one in a bit more detail.
What is Settlement? (pressing down)
Settlement is a natural process that occurs during the first few years of many buildings. The weight of the property presses down on the ground below, causing it to sink, or settle, a little.
Normally this is a uniform process that happens to the entire building. This means it does not tend to compromise the structure. Any cracks that do emerge are usually minor, and can be patched or plastered over once the settlement has stabilised.
However, the ground settles unevenly it can cause more serious issues.
What is Heave? (rising up)
Heave is the opposite of subsidence, where the ground beneath a building rises up rather than falling.
This can be caused by flooding or water leaks, or by trees near the property. Even removing a mature tree can cause heave as the soil expands into the space.
What is Landslip? (moving sideways)
Landslip occurs when the ground beneath a property moves sideways, usually downhill, as a result of erosion elsewhere. This is common on coastal properties and properties built on sloping land.
Natural settlement is often confused with subsidence, but will not normally cause any structural problems
2. What causes subsidence?
There are a number of common causes of subsidence. They generally split into two categories: Factors from the local environment, and factors with the building itself.
2.1. Environmental factors that can cause subsidence
- Subsoil shrinkage. Clay soils are made up of around one third water. If this dries out it will significantly reduce in volume
- Nearby trees. Mature trees can pull water from the ground and this can cause problems, particularly in clay soils. Tree roots can also destabilise the ground beneath a property.
- Water leaks. Burst pipes or faulty drains can cause water leakage which washes away smaller soil particles in fine and sandy soils
- Erosion issues. Soils or bedrock below the property can become eroded, causing caverns that ultimately collapse, leading to sink holes and subsidence issues
- Mining. urrent or historic mining can cause subsidence if tunnels collapse or weaken the subsoil above them
It’s not just local environmental factors that can cause subsidence though. Factors with the property itself can also be causes.
2.2. Property-related factors that can cause subsidence
Subsidence can happen to almost any type of property, in any location. However, certain types of property in certain areas are more prone than others. Factors that can increase the risk of subsidence include:
- Property age. Older properties may not have the same quality or depth of foundation as newer homes and so are more susceptible to subsidence.
- Poor groundworks. If the groundworks (i.e. the foundations) are not done correctly before building, this can lead to subsidence problems. For example, if the wrong fill material is used or the fill is not properly compacted before building starts.
- Local climate. Areas that are prone to drought or to flooding are more at risk as this can cause excessive drying or soaking of the soil.
- Local soil type. Predominantly clay soils are more prone to subsidence issues. There are distinct areas in the South and East of England where subsidence is more common.
- Local history. Areas with a history of mining can be prone to subsidence, even if the mines are now closed.
3. What are the signs of subsidence?
The main signs of subsidence are cracks appearing in your walls, especially around doors and windows, or where extensions meet existing buildings. Other signs include ill-fitting doors and windows, and rippling wallpaper.
Cracks are common in walls for all kinds of reasons (see below), but cracks specifically due to subsidence have a number of telling characteristics:
- Width. Subsidence cracks are normally wider than 3mm (the width of a 10p coin) and wider at the top than at the base.
- Angle. Subsidence cracks are usually diagonal.
- Penetration. Subsidence cracks often go right through the walls. This means they can be seen from both inside and outside the property.
- Location. Subsidence cracks usually appear close to doorways and windows.
Cracks aren't the only sign that your property may be suffering from subsidence though.
3.2. Ill-fitting doors and windows
Subsidence can change the shape of frames, causing doors and windows to stick or not to close as cleanly as they used to. In severe cases, door and window frames may be noticeably off from their true lines.
3.3. Rippling wallpaper
As walls move during subsidence, wallpaper may start to show ripples or even tears. The same can happen with tiled walls, with cracks appearing in grout or gaps appearing or narrowing between tiles.
3.4. Do all cracks mean subsidence?
Fortunately, not all cracks mean subsidence. Cracks can emerge quite innocently from far less serious causes. For example:
- Settling. As discussed above, some degree of settling is natural after a home is built.
- Heat and cold. The materials that make up your home will expand in warm weather and contract when it gets cold. This can cause cracking but is not structurally serious.
- Lintel failure. Supporting lintels over doors and windows can fail causing diagonal cracks similar to subsidence
- Poor joining. If an extension or conservatory is not properly connected to the main building, cracking can occur between the two
4. How to fix subsidence
Subsidence must never be ignored and should be fixed as soon as possible. Unfortunately the longer you leave it, the more the repairs will eventually cost.
That said, subsidence repairs are not always as expensive as you may expect.
According to data from the Association of British Insurers, the average insurance claim for subsidence is around £6,250.
However, if you ignore it the costs can rise significantly. If your property ends up requiring underpinning, it can end up costing more than £10,000-£50,000 to fix (or even more in some cases)
We've written more about the cost of subsidence here:
Related: Is subsidence expensive to fix?
Never ignore subsidence as the problem will only get worse and become more expensive to fix. To resolve an issue with subsidence there's a relatively simple set of steps to follow. (Unfortunately, it can just take a long time to fix subsidence).
Step 1. Expert assessment
The first step in fixing subsidence is to get an expert assessment of the problem. A structural engineer will visit your property to view the symptoms first-hand.
Unfortunately this can be a long, drawn out process, as they may need to monitor cracks and other signs over months or even a year or more. Monitoring the cracks over time helps them identify the nature and magnitude of the problem.
They will then recommend the most cost-effective solution.
Step 2. Fix the cause
The next step in fixing a subsidence issue is to address the problem that is causing it in the first place.
This may not always be possible, such as mining subsidence or soil types, but in many cases it is. Removing the cause stops the problem getting worse and may be all that is needed.
For example, subsidence often can be solved by:
- Managing trees – removing or trimming trees can make a big difference. However, you need to consult a qualified tree surgeon or you could make matters worse.
- Fixing drains and leaks – stopping water from reaching your foundations will prevent further erosion of the subsoil
In some cases, this will be all that's needing. Removing the root cause sometimes makes everything ok. The structural engineer will monitor your subsidence symptoms over the coming months to make sure the problem's stabilised and is no longer getting worse
In other cases, the damage will already have been done, and you'll need to reenforce the foundations before putting the chapter behind you.
Step 3. Re-secure the building
Resolving the root cause won't always be the final step. For example, imagine a burst drain which caused soil to erode and wash away, and this caused subsidence. Even after that burst pipe is fixed, you've still got a void that needs filling.
Re-securing the building can be expensive, and will sometimes mean that underpinning is required.
What is Underpinning?
In severe cases of subsidence, the solution is usually underpinning a house. This involves the removal of the subsoil beneath each wall and replacing it with a more stable foundation material.
This may mean pouring new concrete, or it may mean inserting steel “pins” into the foundations.
Unfortunately, underpinning is a disruptive and expensive process.
Can subsidence be fixed without underpinning?
The good news is that underpinning is only used as a last resort in the worst-case scenarios. Most of the time, subsidence can be repaired without underpinning.
In fact, in their consumer guide, the Royal Institute of Chartered Surveyors estimated that “less than 10% of properties suffering from subsidence need underpinning”.
The Institution of Structural Engineers agrees, recommending underpinning only as a last resort.
In most cases, the root cause can be remedied and the cosmetic repairs carried out, and no expensive ground works will be required.
However, even if ground works are necessary, there are new alternatives to underpinning coming to market.
In recent years, new technologies from the likes of Geobear have emerged that replace the need for underpinning. This process involves injecting resin into the ground around the building, which then hardens like concrete in as little as 15 minutes.
The process is faster and less disruptive than underpinning, and does not need to be declared to insurers, mortgage companies or future buyers.
Your structural engineer and insurer will be able to help guide you on which solution will be right for your property.
Step 4. Repair the cosmetic damage
Finally, once the environmental factors have been resolved and the foundations have been secured, any cosmetic damage can be repaired.
This will involve plastering over cracked areas, replacing wallpaper, re-setting doors and windows, and so on.
5. Is subsidence covered by home insurance?
Most buildings insurance policies will cover for subsidence as long as you have undertaken due diligence when purchasing the property in the first place. (This is because your insurer wants to make sure that the problem does not pre-date the start of the policy).
You may find that insurance claims for subsidence carry a larger excess than other types of claims. According to the Association of British Insurers, “Most policies will have an excess of around £1,000 for a subsidence claim”. (This means you’ll have to pay the first £1,000 of any claim, and the insurer will pay the rest).
5.1. What to do if you suspect you may have subsidence
If you suspect subsidence, you should contact your insurer as soon as possible.
They will send out a surveyor to assess the problem and propose solutions.
How much does a subsidence survey cost?
You should expect to pay around £700-£1,000 for a professional structural survey. The cost will be covered by your insurance, but in reality your excess for a subsidence claim is likely to be about the same amount. This means that, in most cases, you should expect to pay for it.
Once the final report has been filed, most insurers will then arrange the repairs with their approved contractors – and ultimately cover the cost of them.
What if you find subsidence while selling your home?
If subsidence is found during the process of selling your home, you can still claim on your insurance.
In fact, some insurers will allow you to transfer the cover to the new owners. This allows you to continue with the sale at (or near to) the original price, while covering the cost for the new owners.
If the discovery of subsidence lowers the sale price, you may be able to claim the loss from your insurers. This varies widely by insurer though, so you should check your policy details carefully to ensure this is the case before proceeding.
Selling a property with subsidence is unfortunately a treacherous and pretty tricky thing to pull off.
Thankfully, we’ve covered it in more detail in our dedicated article on how to sell a home with subsidence. We can even give you personal advice and help you determine the way to sell, and whether or not you should carry out the repairs before selling.
By Matthew Cooper, Founder of Home Selling Expert