A crack in a wall is one of the things buyers worry about most. The good news is that most cracks we see are not subsidence. Some are, though, and it pays to know the difference before you commit to buy. Here’s what causes subsidence, the signs we look for, and how it’s investigated and repaired.
What is subsidence?
Subsidence is when the ground under a house moves downwards and takes part of the foundations with it. It rarely affects the whole house evenly, so one part drops more than another and the walls crack.
It isn’t the same as settlement, which is a newer home bedding in during its first few years and is usually harmless. Nor is it the same as heave, where the ground swells and pushes upwards, often after a large tree has been removed from clay soil.
Common causes
Clay soils drying out. Shrinkable clay contracts in long, dry summers and swells again in winter. Much of Oxfordshire, Berkshire and parts of Hampshire sits on clay.
Trees and large shrubs. Roots draw water out of the soil, especially when they are close to the house. Oak, willow and poplar are particularly thirsty.
Leaking drains. Escaping water can soften or wash away the soil under the foundations.
Shallow foundations. Many older homes have shallow footings, which are more sensitive to changes in the ground.
Old mine workings, quarries or made-up ground. Less common, but a factor in some areas.
The signs to look for
Diagonal cracks that are wider at the top than the bottom, often running from the corners of windows and doors.
Cracks wider than about 3mm, or cracks that show in the same place inside and out.
Doors and windows that stick or have gone out of square.
Cracks that have been filled and reappeared, or that open and close with the seasons.
Gaps opening up between skirting boards and floors, or where an extension meets the main house.
Fine hairline cracks in plaster, or a crack along the line where new plaster meets old, are usually cosmetic.
How we assess it in a survey
We look at the pattern, width and direction of the cracking, the age of any past repairs, nearby trees, ground levels and drainage, and whether doors and frames are out of square. We use a 9-metre pole camera to look closely at chimneys and high walls we can’t reach safely.
No surveyor can tell from one visit whether movement is still active. So where the cracking points to possible subsidence, we say so clearly, rate it Condition Rating 3 (needs investigating now) and recommend a structural engineer looks at it before you commit to buy. We also suggest asking the seller about any past insurance claims, monitoring or repairs, and whether a certificate of structural adequacy was issued.
How subsidence is investigated
A structural engineer, often appointed by the insurer, will usually:
Measure and record the cracks.
Monitor them over several months, often through a full year, to see whether they are still moving.
Dig trial pits to look at the foundations and the soil beneath them.
Survey the drains with a CCTV camera to check for leaks.
Assess nearby trees, sometimes with root and soil tests.
How it’s repaired
The aim is to stop the cause first, then repair the damage.
Deal with the cause. Repair leaking drains, or remove or reduce problem trees. Always get advice before felling a large tree near a house on clay, as removing it can cause heave.
Monitor until the ground has settled down.
Repair the cracks. This usually means stitching the brickwork or stonework with stainless steel bars, repointing, replastering and redecorating.
Underpin only when needed. Deepening or strengthening the foundations is far less common than many people think. It’s used when dealing with the cause isn’t enough.
Buying a house that has had subsidence
Past subsidence isn’t automatically a reason to walk away. If it was properly investigated, the cause was dealt with and the repairs were signed off, the house may be perfectly sound. Ask your solicitor to get all the paperwork, and speak to insurers and your lender before you exchange, as some will want more detail or charge more.
Questions we’re often asked
Is every crack subsidence?
No. Most cracks we see come from settlement, plaster or timber drying out, or seasonal expansion and contraction. They are cosmetic and simple to repair.
Will a Level 2 survey pick up subsidence?
A Level 2 will flag visible cracking and movement. For older or altered homes, or where there is a history of movement, a Level 3 Building Survey explains likely causes and what to do next in more detail.
Can I get a mortgage on a house that has had subsidence?
Often, yes, particularly where repairs are complete and signed off. Lenders and insurers vary, so raise it early.
How we help
We only book one survey a day, so we have time to look properly at every crack. We explain in plain English what’s normal and what isn’t, and we call you after the inspection to talk it through. With your report, our helpful guides explain your next steps: what to get quoted, what to ask your solicitor and what to raise with the seller.
Worried about cracks in a home you’re buying? Use the Get My Quote button above, or call us on 01451 828107 (Cotswolds) or 01256 578063 (Hampshire).
Max Daniel AssocRICS, Director, MJD Residential Surveying