Signs of subsidence
- Diagonal cracks, often wider at the top, running from the corners of windows and doors.
- Cracks that are visible both inside and outside the same wall.
- Doors and windows that have started to stick, especially in late summer.
- Gaps opening between walls and ceilings, skirting boards or the floor.
- An extension or bay pulling away from the main house.
Some of these have other explanations too. That is why a proper investigation looks for the cause, not just the cracks.
Why London homes are prone to it
Much of London is built on clay that shrinks as it dries and swells when it is wet. Victorian and Edwardian houses often have shallow foundations, so they respond to that movement. Trees and large shrubs draw water from the clay, which is why subsidence claims rise after hot, dry summers. Leaking drains are the other common cause: escaping water can soften or wash away the soil under a foundation.
How we investigate
On a General Structural Inspection the engineer records and measures the cracking and looks at its pattern to see which part of the building is moving and in which direction. Trees and shrubs near the house are assessed against NHBC guidance on foundations near trees, and the soil is checked against British Geological Survey records.
Your report sets out the likely cause, whether the movement appears historic or ongoing, and what should happen next. Where the evidence from a single visit is not enough, we say exactly what would settle it:
- A CCTV survey of nearby drains.
- Trial holes to expose the foundations and sample the soil.
- Crack monitoring over several months.
- Advice from an arboriculturist on the trees involved.
Subsidence and your insurer
If you think your home is subsiding now, tell your buildings insurer early. Most policies cover subsidence, and the insurer will usually appoint its own investigators. An independent report from us is useful when you are buying or selling, when you want a second opinion, or when you need to show a new insurer that past movement has stopped. See insurance structural reports.
Case studies
- Conservatory separating from a house in Uxbridge. A rear conservatory in Uxbridge, UB8, with a history of movement and an 8 to 20 mm gap at the house wall. What we found and why removal was the sensible option.
Common questions
Does subsidence always mean underpinning?
No. Most subsidence is dealt with by removing the cause, such as managing a tree or repairing a drain, letting the ground stabilise and then repairing the cracks. Underpinning is only needed in a minority of cases, usually where the cause cannot be removed or the foundations are inadequate.
What is heave?
Heave is the opposite of subsidence: clay swelling and pushing foundations upwards, often after a large tree has been removed. Cracks from heave tend to be wider at the bottom. It is one reason why trees should not be felled without advice.
Will a house with past subsidence sell?
Usually, yes, provided the movement has stopped and the repairs are documented. Buyers and lenders want to see evidence, which is where a current engineer's report helps.
How quickly will I get the report?
Usually within 5 working days of the inspection. This is our normal turnaround, not a guarantee: at busy times, or when we are waiting for information, it can take longer, and we will tell you if it will. If you are working to a deadline, fast track brings it to within 48 hours of the inspection, from £120*.
