Signs Your House Needs Structural Repairs: What to Look For

A structural problem is any defect that affects the load-bearing elements of a building — the foundations, walls, beams, columns, roof structure, or floor structure. These are the elements that carry the weight of the building and transfer it to the ground. When they're compromised, the building can move, crack, or in extreme cases, collapse.

Structural problems are distinct from cosmetic problems. A hairline crack in plasterwork caused by thermal movement is cosmetic — it doesn't affect the structural integrity of the building. A diagonal crack running from the corner of a window opening down to the floor, widening as it goes, is structural — it indicates differential movement in the wall below, which could be caused by subsidence, foundation failure, or overloading.

According to the Building Research Establishment (BRE), subsidence affects approximately 5% of UK properties at some point in their lifetime, with the highest incidence in areas underlain by clay soils — including much of Hertfordshire. The BRE's guidance document BRE Digest 251: Assessment of Damage in Low-Rise Buildings provides the standard framework used by structural engineers and insurers to classify crack severity.

The key distinction is between active movement (where the building is still moving) and historic movement (where movement has stopped and the building has stabilised). Active movement requires investigation and remediation. Historic movement may require repair but not necessarily structural intervention — the building has already found its new equilibrium.

Diagonal cracks running from the corners of window or door openings are the most common sign of differential settlement — where one part of the foundation has moved more than another. On clay soils, this is often caused by tree root desiccation (tree roots drawing moisture from the clay, causing it to shrink) or by seasonal moisture variation. Diagonal cracks that are wider at the top than the bottom indicate the wall is dropping on the side where the crack is widest.

Vertical cracks in the middle of a wall can indicate that the wall has been overloaded, that a lintel above an opening has failed, or that the wall has been affected by thermal movement. Vertical cracks in cavity walls at the junction between the inner and outer leaf can indicate that the wall ties have corroded and failed — a common problem in houses built between 1945 and 1980 using galvanised steel ties.

Horizontal cracks in brick or blockwork walls are the most serious type. They typically indicate that the wall is being pushed outward by the roof structure or floor structure — a condition known as wall spread. Horizontal cracks at the level of the first floor ceiling in a terraced or semi-detached house can indicate that the roof is spreading and pushing the walls outward, which is a serious structural problem requiring urgent attention.

Stair-step cracks following the mortar joints in brickwork are characteristic of differential settlement. They're less serious than diagonal cracks through the bricks themselves, because the mortar is weaker than the bricks and will crack first — but they still indicate movement that needs to be investigated.

Sticking doors and windows are one of the earliest signs of structural movement. When a building moves, the door and window frames distort, causing the door or window to stick or bind. If multiple doors or windows in the same area of the house start sticking at the same time, this is a strong indicator of localised movement.

Sloping floors in older properties are often historic and not a cause for concern — many Victorian and Edwardian houses have floors that have settled over 100+ years. However, a floor that has recently started sloping, or one where the slope is increasing, indicates active movement that needs investigation. A simple spirit level test can confirm whether a floor is sloping and by how much.

Roof sagging visible from the exterior — where the ridge line is no longer straight, or where the roof slopes appear uneven — can indicate that the roof structure is failing. This can be caused by rafter decay (particularly in older properties where the roof has not been ventilated adequately), by the removal of internal walls that were providing lateral restraint to the roof, or by overloading from heavy roof coverings.

Damp patches on walls can indicate structural problems if they're in locations that don't correspond to obvious water ingress routes (leaking pipes, failed gutters, or rising damp). Damp patches on internal walls at high level can indicate that the roof structure is moving and creating gaps in the roof covering. Damp patches at the base of walls can indicate that the damp proof course has been bridged or has failed.

Call a structural engineer when you see Category 3 or above cracks (5mm or wider), when doors or windows are sticking in multiple locations simultaneously, when you can see visible roof sagging, or when you're concerned about any crack that is actively widening. A structural engineer will assess the severity of the damage, identify the likely cause, and recommend appropriate remediation.

A structural engineer's assessment typically costs £500–£1,500 for a residential property, depending on the complexity of the problem and the extent of the investigation required. This is a small cost relative to the cost of remediation — and relative to the cost of buying or selling a property with an undiagnosed structural problem.

If you're buying a property and the survey has flagged structural concerns, always commission a specialist structural engineer's report before exchanging contracts. A standard RICS HomeBuyer Report or Building Survey will identify structural concerns but won't necessarily diagnose the cause or recommend specific remediation — a structural engineer's report will.

For properties in Hertfordshire, the most common structural problems are subsidence on clay soils (particularly in areas with mature trees), wall tie failure in cavity wall construction from the 1945–1980 period, and roof spread in Victorian and Edwardian properties where the original roof structure has not been maintained. TCM's structural engineers have extensive experience with all three.

Hertfordshire sits largely on London Clay — a geological formation that is highly susceptible to seasonal moisture variation. In dry summers, the clay shrinks, causing foundations to settle. In wet winters, the clay swells, causing foundations to heave. This cycle of shrinkage and swelling is the primary cause of subsidence in Hertfordshire, and it's significantly exacerbated by the presence of trees within 5–10 metres of the property.

The trees most commonly associated with subsidence damage in Hertfordshire are oak, willow, poplar, and elm — all of which have extensive root systems that can extract large volumes of moisture from the clay. A mature oak tree can extract up to 50,000 litres of water from the soil per year. The BRE's guidance on tree-related subsidence (BRE Digest 298) provides detailed information on the safe distances between different tree species and different foundation types.

Subsidence insurance claims in Hertfordshire are handled by the property's buildings insurer. If you suspect subsidence, notify your insurer before commissioning any repairs — carrying out repairs without insurer approval can invalidate your claim. The insurer will appoint a loss adjuster and a structural engineer to assess the damage and recommend remediation.

TCM Building & Maintenance has a team of structural engineers who assess and remediate structural problems across Hertfordshire. We work with homeowners, insurers, and loss adjusters to diagnose the cause of structural damage, design appropriate remediation, and carry out the repair work to the standard required by Building Regulations and the property's insurer.

For a client in Borehamwood whose Victorian terraced house had developed Category 3–4 diagonal cracks at the rear of the property, our structural engineer identified tree root desiccation as the cause — a mature sycamore in the rear garden was drawing moisture from the London Clay beneath the rear foundations. We designed a scheme of underpinning using mini-piles to a depth of 5 metres below the zone of clay movement, carried out the underpinning in sections to maintain the stability of the structure throughout, and repaired the cracking with lime mortar to match the original pointing. The project completed in 8 weeks and the property passed its subsequent mortgage valuation.

If you've noticed any of the warning signs described in this guide, read our Structural Repairs service page for more detail on our approach, or contact us for a free initial assessment.