Signs of Subsidence and When to Get a Subsidence Survey

The most common signs of subsidence are new or expanding cracks in your plasterwork or outside brickwork, doors or windows sticking, ripping wallpaper and solid ground floors that slope or dip. Spotting new cracks in your home can be alarming, but the Royal Institution of Chartered Surveyors advises that there is rarely any cause for real concern unless the cracks appear suddenly and are more than 3mm wide. If you do spot these signs, get professional advice on the cause before any repairs or redecorating are done.

What subsidence is and what it is not

Subsidence is the downward movement of the foundations of a building due to changes in the supporting strata. This means the ground beneath your home is sinking or washing away, taking your foundations and walls down with it. It is a structural issue that requires professional investigation to stop the movement and repair the resulting damage.

You will often hear the term settlement used alongside subsidence, but they are entirely different things. Settlement can happen as a new building settles into the ground under its own weight after construction. The Federation of Master Builders explains that settlement can cause hairline cracks up to 2mm wide. Subsidence usually means something has actively changed in the ground beneath the property long after it was built.

Another related term is heave. While subsidence is the downward movement of a building, heave is upward ground movement. This happens when the soil beneath a property expands and swells with moisture, pushing the foundations up. Both issues can cause significant structural damage and present very similar signs inside and outside the property.

What causes subsidence

The ground beneath a house can change for several reasons, and the type of soil your property sits on plays a major role. Shrinkable clay soils are highly susceptible to changes in moisture. During dry periods, these clay soils can dry out and shrink, pulling away from the foundations and causing the building to drop.

Trees and large bushes planted too close to a house are the most common trigger for this ground movement. About 70 per cent of subsidence cases are due to tree roots drawing moisture out of shrinkable soil, according to an estimate quoted by the Royal Institution of Chartered Surveyors. As the roots pull water from the earth, the clay shrinks and fails to support the weight of the house.

Water leaks are another major cause of downward ground movement. Water from a broken drain or a leaking water main can saturate the ground beneath your home. Over time, this constant flow of water softens the soil or physically washes it away from the foundations, leaving them unsupported.

Historic mining can also cause considerable ground movement. If your home was built in a former coal mining area, old tunnels and shafts left deep underground can eventually collapse and cause the ground on the surface to sink. You can check whether a property is in a former coal mining area and order a specific mining report to understand the risks before you buy.

Signs of subsidence to look out for

Not every crack means your house is moving. However, certain types of damage should prompt you to seek professional advice rather than attempting to diagnose the problem yourself. The following signs indicate that the ground beneath your property may be shifting.

Look out for these specific signs inside and outside your home:

• Cracks that appear suddenly and are wider than 3mm.
• Cracks that run in a diagonal direction, especially around doors and windows.
• Cracks that are noticeably wider at the top than they are at the bottom.
• Cracks that are visible on both the inside plasterwork and the outside brickwork.
• Cracks found exactly where an extension joins the main part of the house.
• Cracks that are actively getting longer or wider over time.
• Doors and windows that suddenly start sticking or rubbing against their frames.
• Solid ground floors that begin sloping or dipping in certain areas.
• Wallpaper that is ripping or rippling with no sign of damp behind it.

If you notice these signs, resist the urge to simply paint over them. Filling or painting over cracks will not stop any movement and can hide the symptoms a professional needs to see.

Cracks that are usually nothing to worry about

It is perfectly normal for houses to move slightly as materials expand and contract. Hairline cracks are common in most homes and are rarely a sign of a structural defect. These tiny cracks are usually less than 2mm wide and can appear for several harmless reasons.

Fresh plaster drying out will often develop fine hairline cracks as it loses moisture. Seasonal movement and natural temperature changes throughout the year also cause building materials to expand and shrink slightly, leading to minor cosmetic cracking. Normal settlement in newly built homes or recent extensions will also cause small cracks to form.

If you are unsure about a crack, or one starts to open up or run diagonally across a wall, or nearby doors start to jam, note when you first saw it and get professional advice before you fill or paint over it.

What to do first if you suspect subsidence

If the damage to your property looks serious, active or structural, your buildings insurer may be the first call you need to make. Subsidence is often covered by standard buildings insurance, but policies vary widely. You should check your specific policy documents to see what is included for investigation and repair.

Once you suspect the ground is moving, do not spend any money on cosmetic repairs. Filling cracks or replacing torn wallpaper can hide the symptoms, making it much harder for a professional to diagnose the cause. You must wait until the cause has been thoroughly investigated and resolved before you decorate.

If you suspect a large tree is causing the problem, do not cut it down immediately. The Federation of Master Builders warns that trees should not be removed without proper advice. Removing a tree in the wrong situation can sometimes make ground movement worse rather than better.

How subsidence is investigated and monitored

When you report suspected ground movement to your insurer, they will usually send a professional to inspect the damage. The insurer may send a loss adjuster, a surveyor or a structural engineer to look at the cracks, check the drains and assess any nearby trees. Their job is to find out exactly what is causing the movement and whether it is an ongoing problem.

The professionals will need to determine whether the movement is active or historic. Active subsidence means the property is still moving and requires a formal investigation and a repair plan. Historic movement means the ground has completely stopped shifting. If the movement is historic, you may only need to gather evidence, keep monitoring records or carry out cosmetic repairs.

Investigating active movement is not a fast process. Cracks may need monitoring for as long as 12 months, or even longer in extreme cases, to see how they change across different seasons. The Royal Institution of Chartered Surveyors notes that solving subsidence can take up to two years to investigate fully and put right. If you are unsure whether to use a surveyor or an engineer for a private assessment, our guide explains when to consult a structural engineer.

How it is repaired and what it costs

Most cases of ground movement are fixed by dealing directly with the root cause, followed by standard crack repairs. If a broken drain is washing soil away, repairing the leaking pipework is often enough to stabilise the property without any need for major structural work. If tree roots are the issue, managing or removing the trees under professional guidance can solve the problem.

In more severe cases, contractors may use resin injection to stabilise the ground beneath the foundations. The most drastic repair is underpinning, which involves digging beneath the current foundations and filling the space with concrete to strengthen them. The Royal Institution of Chartered Surveyors points out that fewer than 5 per cent of properties with subsidence actually need underpinning. The Institution of Structural Engineers recommends underpinning only as a last resort.

The table below shows typical published figures for private structural inspections and underpinning. These figures give you an idea of the costs if you are paying privately rather than claiming through insurance.

The underpinning range combines two published ranges. Local quotes will differ based on the size of your property, the complexity of the damage and your location.

Buying or selling a home with a subsidence history

Ignoring signs of ground movement is a costly mistake. Leaving the problem unresolved can lead to wider structural damage and much higher repair costs down the line. It can also make it harder to get buildings insurance or a mortgage in the future.

If your home has had confirmed subsidence, you will usually need to disclose it when selling the property. Buyers and their mortgage lenders will want to see comprehensive documents proving that the problem was handled correctly. You must be prepared to provide structural reports, insurance records, repair records and long term monitoring evidence to show that the movement has stopped.

If you are buying a home and your survey mentions movement or past subsidence, ask the seller for these documents and pass them to your conveyancer and your surveyor for review. If the movement may be active, ask your surveyor what further investigation is needed before you commit, then decide with your conveyancer whether to proceed, walk away or renegotiate the house price.

Common questions

Does house insurance cover subsidence?

Subsidence is often covered by standard buildings insurance, but policies vary between providers. You must check your specific terms to see what investigation and repair work is included. Subsidence claims usually have a higher excess than standard claims, and the Royal Institution of Chartered Surveyors notes that this excess is commonly £1,000.

Can subsidence be fixed without underpinning?

Yes, the vast majority of cases are fixed without underpinning. Fewer than 5 per cent of properties with subsidence require underpinning to stabilise them. In most cases, repairing leaking pipework or safely managing nearby trees is enough to stop the ground moving so that normal crack repairs can be carried out.

What is the difference between subsidence and settlement?

Subsidence is the downward movement of the ground beneath a building due to changes in the soil, such as moisture loss or leaking drains. Settlement happens as a newly built property or extension naturally settles into the ground under its own weight. Settlement can cause hairline cracks up to 2mm wide, while subsidence cracks tend to be wider than around 3mm or keep getting longer or wider.

What to do next

If you have found worrying cracks or suspect your property is moving, you should take a methodical approach to protect your home and your finances. Follow these steps to ensure you get the right advice.

• Note when you first noticed each crack, sticking door or other sign, so you can tell the professional.
• Do not fill the cracks or redecorate until the root cause has been found.
• Check your buildings insurance policy to confirm your cover and your excess amount.
• Contact your insurer if the damage looks serious, active or structural.
• Do not remove any large trees near the property without professional advice.
• Gather any previous structural reports or insurance records if you are selling the home.

Getting professional advice early is the best way to find the cause and limit further damage. Whether you are dealing with a property you already own or one you are hoping to buy, you should always rely on expert advice. To get started, you can find a surveyor near you to discuss an inspection and put your mind at rest.