Subsidence: what a survey can (and can't) tell you

A house survey can tell you whether a property shows signs of movement, such as cracking, distortion or sloping floors, and give a professional view on whether that movement looks old and stable or recent and possibly ongoing. What it cannot do is prove whether subsidence is active right now. That usually needs a structural engineer, investigation of the ground and drains, and sometimes months of crack monitoring.

Key points

• Surveyors look for patterns of cracking and distortion, not just individual cracks.
• Historic movement that has stabilised is common in older homes and often not a problem.
• Active subsidence usually needs a structural engineer to confirm and investigate.
• Past subsidence affects insurance, so check cover before you exchange.
• Clay soils, nearby trees and leaking drains are the most common triggers in England.

What is subsidence?

Subsidence is the downward movement of the ground beneath a building's foundations, which causes part of the building to drop. In England and Wales the most common causes are:

• Shrinkable clay soils that dry out and contract in hot, dry summers, especially across London and the South East.
• Trees and large shrubs drawing moisture from clay soils near foundations.
• Leaking drains or water mains washing away or softening the ground.
• Mining and natural cavities in some areas, covered in our guide to buying in a former coal mining area.

It is different from settlement, which is the normal bedding down of a new building in its first few years, and from heave, where clay swells and lifts the building, often after trees are removed.

What does a surveyor look for?

During a Level 2 Home Survey or Level 3 Building Survey, the surveyor looks for evidence of structural movement inside and out. Typical signs include:

• Diagonal cracks, especially those that taper (wider at one end) running from the corners of windows and doors.
• Cracks that are visible on both the inside and outside of the same wall.
• Doors and windows that stick or have been planed down, and frames that are out of square.
• Gaps between walls and ceilings, skirting boards or floors.
• Sloping floors and walls that lean or bulge.
• Brickwork that has been repointed or patched in a way that suggests earlier cracking.
• Large trees within influencing distance of the house, and evidence of drainage problems.

The surveyor puts these observations together. One fine crack on its own tells them very little. A consistent pattern of tapering cracks on one corner of the house, close to a large oak on clay soil, tells them a great deal. Our guide on cracks in walls explains which cracks typically concern surveyors.

What can't a survey tell you?

A survey is a visual inspection on a single day. The surveyor will not dig trial holes, CCTV the drains, test soil samples or monitor cracks over time. That means they usually cannot say with certainty:

• Whether movement is still happening.
• What is causing it, if there are several possible causes.
• How deep or adequate the foundations are.
• Whether previous repairs, such as underpinning, were done properly.

Where the evidence suggests possible ongoing movement, a good surveyor will say so and recommend further investigation by a structural engineer. That recommendation is not the surveyor avoiding responsibility. It reflects the limits of what can be seen without invasive work.

Level 2 or Level 3 if you are worried about movement?

If you already know the house has had subsidence, has been underpinned, sits on clay near big trees, or shows obvious cracking, a Level 3 Building Survey is usually the better choice. It gives a fuller description of the structure, more discussion of likely causes and clearer advice on what to do next. For a straightforward modern house with no obvious issues, a Level 2 will normally pick up signs of movement that need following up. See Level 2 vs Level 3 if you are deciding.

What happens if movement is flagged?

1. Speak to the surveyor. Ask whether they think the movement is historic or recent, what they think the cause is and how urgent further investigation is.
2. Ask the seller questions. The seller's property information form (TA6) asks about past subsidence, structural movement and insurance claims. Ask for any claim correspondence, engineer reports, monitoring records and guarantees.
3. Instruct a structural engineer. They can assess the cracking in more detail, and may recommend drain surveys, soil tests or crack monitoring. Monitoring often takes months, which may not fit your purchase timescale.
4. Check insurance early. Get buildings insurance quotes before exchange. Some insurers decline properties with past subsidence or apply higher excesses. Staying with the seller's insurer can sometimes help.
5. Talk to your lender. If the lender's valuer has also noticed movement, the mortgage offer may be delayed until a structural engineer's report is provided.
6. Decide and negotiate. Use the findings to renegotiate or, if the risk is too great, to walk away. Our guides on renegotiating after a survey and whether to pull out may help.

Is a house with past subsidence a bad buy?

Not necessarily. Many older homes have moved at some point and stabilised decades ago. Properties where subsidence was claimed on insurance, the cause was dealt with (for example a tree removed or drains repaired) and the house was repaired with a certificate of structural adequacy can be perfectly good buys, often at a discount.

The risks to weigh up are:

• Insurance cost and availability, now and when you come to sell.
• Resale, since future buyers will ask the same questions.
• Recurrence, if the original cause has not been fully addressed.

If you have the paperwork, a clear explanation of what happened and affordable insurance, past subsidence may be something you can live with.

How much does dealing with subsidence cost?

Costs vary hugely. Removing a tree or repairing a drain might cost a few hundred to a few thousand pounds. Crack repairs and redecoration after the cause is fixed are usually moderate. Underpinning is the expensive end and can run to tens of thousands of pounds, which is why insurers often prefer to deal with the cause and monitor before underpinning.

If you want a surveyor to look closely at a property before you commit, you can get a fixed-price survey booked with a local RICS or RPSA regulated surveyor, and we will arrange access with the agent.

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