The signs most likely to point to a structural problem in a house are cracks wider than about 3 mm, especially diagonal cracks that are wider at the top and appear near doors and windows; doors and windows that start sticking for no obvious reason; floors that slope noticeably; walls that lean or bulge; and a roof line that dips. Fine hairline cracks, by contrast, are usually cosmetic and can be dealt with when you redecorate.
If you see any of the more serious signs, the next step is a professional opinion rather than a guess. For a buyer that usually means the right level of RICS home survey and, where the surveyor recommends it, a structural engineer. For an owner it means contacting your buildings insurer early if you suspect subsidence. Ground conditions matter too: clay soils shrink in dry weather and swell when wet, and the Gault Clay that runs through the Cambridge area is one of the clays the British Geological Survey (BGS) rates as highly prone to this. This guide explains what each warning sign can mean, what to do about it, and what sellers have to tell buyers.
One sign on its own is not proof of a structural fault, and several of these can have everyday causes. What matters is the pattern, the size of any movement and whether it is getting worse.
The Building Research Establishment (BRE) classifies visible damage to walls into six categories in its Digest 251, Assessment of damage in low-rise buildings, which is widely used in the industry. Crack width is the starting point:
BRE describes categories 0 to 2 as "aesthetic" issues that need only redecoration, categories 3 and 4 as "serviceability" issues, and category 5 as a "stability" issue likely to need structural work. Width is not the whole story, though. BRE notes that several factors, including whether cracks are getting wider over time, can change the classification. So a crack that keeps opening deserves attention even while it is still narrow.
The Association of British Insurers (ABI) lists the cracks most associated with subsidence as those more than 3 mm wide, running diagonally and wider at the top than the bottom. The BGS adds that subsidence cracks are typically visible from both inside and outside and often occur near doors and windows. The ABI also says that cracks appearing suddenly, rather than gradually, can be a sign of subsidence.
The BGS points out that cracks can appear for reasons other than subsidence. A building settling under its own weight can crack walls, especially in newly built homes and extensions. Cracks under 5 mm fall within BRE's aesthetic categories, but these describe the repair needed, not the cause, so a diagonal crack of 3 to 5 mm can still point to subsidence. Horizontal cracks, stepped cracks through brickwork mortar and cracks around bay windows or chimneys can have a range of causes, so ask a surveyor to interpret any pattern you are unsure about. Our guide to what cracks mean for your home covers this in more detail.
A simple habit helps whichever kind of crack you have: photograph it with a ruler alongside and note the date, then check it again over the following weeks and months. The ABI says it may be necessary to monitor movement to find the underlying cause, and an insurer's engineer may do this formally over a period of time.
BRE links slight sticking of doors and windows with category 2 damage, sticking with category 3, and distorted frames, noticeably sloping floors and walls leaning or bulging with category 4. The ABI and the Institution of Structural Engineers (IStructE) both list doors and windows sticking, or becoming harder to open or close, as a sign of subsidence.
The useful questions are whether the problem is new, whether it is getting worse, and whether it lines up with cracking nearby. A door that has always rubbed is very different from one that started jamming last summer alongside a new diagonal crack above it.
Floors that feel springy or have dropped in one area are worth flagging to your surveyor, who can look more closely at a Level 2 or Level 3 survey (see below).
Stand back from the house and look along the ridge and the roof slopes. A visible dip, or slopes that look uneven, is worth pointing out to your surveyor so the roof structure can be checked. If you can see into the loft, point out any staining or damp on the timbers too.
Ask whether the roof has been re-covered. The government's Planning Portal says that where a new roof covering is significantly heavier or lighter than the old one, the roof structure may need modifying or strengthening, and Building Regulations approval is likely to be needed. It advises checking with a structural engineer or surveyor before work starts. If a roof has been re-tiled in a heavier material, ask whether approval was obtained.
Spray foam insulation on the underside of roofs is another thing to ask about. RICS describes it as something that "should be viewed as a serious modification", and its consumer guide covers the condensation and damp risks it can create. If the loft has been sprayed, ask the seller for details of the product, the installer and any paperwork.
Damp is not just a decoration problem. Historic England, writing about timber-framed buildings, notes that decay fungi can cause structural defects, that structural timber is vulnerable to fungal and insect attack when its moisture content stays above about 27 to 28 per cent for a long period, and that problems arise when moisture is trapped and cannot escape. Kept dry, structural timber can last for centuries.
Point out to your surveyor anything that suggests timbers are staying damp, such as a musty smell, soft floorboards or skirting, fungal growth or persistent staining around roofs, gutters and windows. Leaks also affect the ground: the ABI says leaking drains and water mains can wash away or soften soil beneath foundations, and IStructE notes that tree roots can damage drains, which then leak and make subsidence worse.
The ABI defines subsidence as the ground beneath a building sinking and pulling the foundations down with it. Heave is the opposite: an upward movement of the ground supporting the building. Landslip is ground moving down a slope.
On clay, both are driven by moisture. The BGS explains that clay-rich soils swell as they take up water and shrink and crack as they dry, and that this shrink-swell behaviour is the most damaging geohazard in Britain today. Damage happens when the movement is uneven beneath the foundations. The BGS lists the main triggers as normal seasonal changes in rainfall and vegetation; planting, severe pruning or removal of trees or hedges; changes to drainage and paving; and leaks from water pipes or drains. Dry weather and high temperatures are a major factor, and the BGS expects more properties to be affected if summers become warmer and drier, as climate projections suggest.
Recent figures reflect this. The ABI reported that insurers paid £72 million on domestic subsidence claims between April and June 2026, with the average claim reaching a record £20,000, after the warmest spring on record in England and Wales.
The BGS says the rock formations most prone to shrink-swell are found mainly in the south-east of Britain. One of them is the Gault Formation, also known as the Gault Clay, which the BGS describes as forming a narrow outcrop extending southwards from Hunstanton to Cambridge and beyond. The BGS says the Gault is prone to shrink-swell because parts of it contain significant amounts of smectite clay, and that outside the south-west of England almost all of its outcrop falls in the "very high" expansive potential category.
Ground conditions still vary from street to street. The BGS also notes the Chalk escarpment near Cambridge, and across much of East Anglia the bedrock is covered by later deposits. So rather than assume, check what is mapped for the area and ask your surveyor about the ground:
IStructE says buildings on shrinkable clay with shallow foundations, such as conventional unreinforced strip or raft foundations, are the most vulnerable. The BGS adds that areas with many older houses and old-style shallow foundations can be seriously affected, which is one reason older properties on clay deserve a thorough survey.
Trees and large shrubs take water from the soil, and on clay that can dry the ground enough to cause movement. The BGS says this mostly happens in spring and summer, and that the zone of seasonal moisture change is usually the top 1.5 to 2 metres of ground but can reach 5 metres, with tree roots greatly influencing the depth.
The answer is not simply to cut trees down. The BGS lists tree removal among the triggers of clay movement, because long-dried ground that rewets can swell and cause heave. BGS advice for homeowners on shrinkable clay is:
Some trees are also protected. Under government guidance, a Tree Preservation Order prohibits cutting down, topping, lopping, uprooting or wilfully damaging the tree without the council's consent, and cutting roots also needs consent. In a conservation area you must normally give the council 6 weeks' notice before carrying out certain work on trees. Where an application to work on a protected tree is made because of alleged subsidence, the council expects evidence that the tree is a material cause of the problem. Check with the council before anyone starts work.
Not all structural problems come from the ground. IStructE says removing or altering a load-bearing wall is one of the most common structural changes in homes, and that the replacement support, often a steel beam, has to carry the loads down to the foundations.
The TA6 asks sellers about exactly these alterations, including extensions, loft and garage conversions, removal of internal walls and removal of chimney breasts, and the Law Society's notes say alterations can affect a property's use, stability or value. The notes also say buyers will often need Building Regulations approvals and completion certificates for building work, so if a house has had this kind of work, ask for them and for any structural engineer's calculations.
The RICS Home Survey Standard sets out three levels of survey, which RICS members and regulated firms in the UK must follow:
For a period house, a much-altered house or one showing any of the warning signs above, a Level 3 survey is usually the sensible choice. RICS has said a second edition of the standard is in draft and it intends to publish it in early 2027, so the current edition still applies. Our guide on which home survey you need goes through the choice in more detail, and our viewing checklist will help you spot problems before you make an offer.
Do not rely on your lender's valuation. The TA6 itself tells buyers who are getting a mortgage not to rely on any inspection or valuation carried out for the lender, and to instruct a surveyor so they understand the property's physical and structural condition.
If the survey flags significant cracking, movement or alterations it cannot assess, a structural engineer can investigate the cause and recommend a fix. IStructE recommends its Find an Engineer directory for finding a professionally qualified structural engineer. Get the report before you exchange contracts: the RICS standard says Level 2 reports should make clear that further advice the surveyor recommends should be obtained before the buyer enters into a legal commitment.
The current TA6 (6th edition), which firms in the Law Society's Conveyancing Quality Scheme must use where they were instructed on or after 30 March 2026, does not have a single question headed "structural problems". Structural matters come up in several sections instead:
The form tells sellers to answer truthfully, completely and as accurately as they can from their own knowledge, and to say so if they do not know an answer. It warns that if you give misleading information, the buyer may be able to claim compensation after completion. A past subsidence claim (question 7.3) or an underpinning guarantee (question 6.1) must be answered accurately, and section 15 of the form lets you add further information and documents, such as an engineer's report. Our guide to how long you are liable after selling a house explains the time limits for claims if an answer turns out to be wrong or incomplete.
If you suspect movement, contact your insurer before you put the house on the market. The ABI says to do this as soon as possible and that subsidence claims can take a number of months to resolve. If the house had a problem that has been fixed, gather the engineer's reports, the insurer's correspondence and any guarantee so your solicitor can send them with the TA6 and your buyer can see what was done and why. When you book a valuation with RAH, tell us about any history so the marketing and asking price reflect it from the start. Under the Digital Markets, Competition and Consumers Act 2024, estate agents must not give buyers misleading information or leave out material information the average buyer needs to make an informed decision, where this is likely to affect that decision.
This article is general information, not structural, insurance or legal advice. Speak to a RICS surveyor or structural engineer about a specific property, your insurer about cover, and a solicitor or licensed conveyancer about what you need to disclose.
Usually, yes. BRE classes hairline cracks under 0.1 mm as negligible and cracks up to 5 mm as "aesthetic" issues that need only redecoration. Keep an eye on any crack that keeps widening, runs diagonally or appears inside and outside the same wall.
The ABI suggests investigating cracks more than 3 mm wide, particularly diagonal ones that are wider at the top. Under BRE's scale, cracks of 5 to 15 mm need repair by a mason, and cracks wider than 25 mm indicate structural damage. Whether a crack is growing matters as much as its width.
The ABI says a standard home insurance policy covers your main home and outbuildings for damage caused by subsidence, heave and landslip. Damage to drives, patios or garden walls alone is generally excluded, and the ABI says most policies have an excess of around £1,000 for a subsidence claim.
That depends on what caused it and how well it was fixed. Get a Level 3 survey, ask for the engineer's reports and any underpinning guarantee, check whether the repair was done under the insurer's direction, and confirm you can get buildings insurance before you exchange contracts.
The TA6 asks whether you have made any buildings insurance claims, whether insurance has been difficult to obtain, and about guarantees such as underpinning. There is no general legal duty to volunteer defects, but your answers must be truthful and complete, you must not hide a problem, and misleading information can lead to a compensation claim after completion.
Take advice first. Removing a mature tree on clay can cause heave, and the BGS suggests crown reduction or thinning may be better. If the tree has a Tree Preservation Order or is in a conservation area, you need the council's consent or must give notice before any work.
