Signs of subsidence in a house: what to look for

What is subsidence?

Subsidence is the gradual sinking or downward settling of a building's foundations, usually caused by changes in the ground beneath it. As the foundations move, the structure above is put under stress, which can show as anything from fine cracks to serious structural instability.

It is a common issue across the UK, particularly in areas with clay soil. It can happen anywhere, and any type of property can be affected, from Victorian terraces to modern new-builds. Left unchecked, it can cause severe structural damage, and repairs could run into thousands of pounds (figures given when this guide was first written).

What are the signs of subsidence?

The clearest warning sign is cracking that follows a particular pattern. Subsidence cracks are typically diagonal, wider at the top than the bottom, thicker than a 10p coin, and often appear where the structure is weakest.

• New or widening cracks, often diagonal and wider at the top.
• Cracks around doors and windows, and where an extension joins the main house.
• Doors or windows that suddenly stick or no longer close properly, which can mean the frame has shifted.
• Sloping or uneven floors.
• Wallpaper that ripples, crinkles or tears at the joints with no sign of damp.

Individually, each of these can have an innocent explanation. Together, and combined with new cracking, they point towards movement.

Seen cracks at a home you are buying? Get a survey price for the home you are buying.

Which cracks are not subsidence?

Hairline cracks are usually not subsidence. They are extremely common and are typically caused by normal settlement, temperature changes or drying plaster.

Subsidence signs are not always obvious to the untrained eye, and even a property that looks perfect from outside may be showing subtle symptoms.

What causes subsidence?

Subsidence is usually caused by changes in the ground beneath a building, and environmental factors play a significant part.

• Clay soil: properties on clay are particularly vulnerable, because clay shrinks and swells as its moisture content changes.
• Trees: trees near a property are a common cause of ground movement.
• Dry weather: dry spells can dehydrate the soil, causing ground movement that leads to subsidence.

Is the subsidence active or historic?

Active subsidence is still happening; historic subsidence occurred in the past and has since stabilised. Telling the two apart usually needs monitoring or a professional assessment.

What to look for when viewing

• Diagonal cracks around doors and windows, and where an extension meets the main house.
• Cracks wider at the top than the bottom, or thicker than a 10p coin.
• Cracks that look new, or older cracks that have been filled.
• Doors and windows that stick or do not close cleanly.
• Floors that feel uneven or sloping.
• Wallpaper rippling or tearing at the joints where there is no damp.
• Trees close to the house, particularly on clay soil.

What to do if you suspect subsidence

The first step for a buyer who spots these signs is a thorough building survey by a qualified surveyor, who will assess whether subsidence is a genuine concern and, if so, whether it is active or historic.

1. Commission a building survey before committing to the purchase.
2. Where active subsidence is found, identify the cause, which can involve a soil investigation or a drainage survey.
3. Agree the treatment. This ranges from simple fixes, such as removing nearby vegetation or trees or repairing leaking drains, to underpinning (strengthening the foundations) in more serious cases.
4. Work with a skilled surveyor and a reliable construction team on any repair.

A property with subsidence need not be written off. Many subsidence problems can be fixed, or at least managed, with professional help; the issue has to be understood before committing.

What a survey can — and cannot — tell you

A building survey provides an informed assessment of the visible condition of a property. Inspections are non-intrusive and limited to areas that are accessible at the time of inspection.

A building survey can identify signs of subsidence and indicate whether movement appears active, historic or of no concern, before a buyer commits.

• The width, pattern and location of cracks.
• Cracking around openings and at the junction with any extension.
• Doors and windows that stick, and floors that slope.
• Older, filled cracks that may indicate past movement.
• Trees and vegetation near the building.

However, there are limitations to what a survey can determine without intrusive investigation.

• Telling active from historic movement can need monitoring over time.
• Identifying the cause can need a soil investigation or a drainage survey.
• Foundations and the ground beneath them are not visible during the inspection.

Where higher-risk indicators are identified, further specialist or intrusive investigation may be recommended.