Structural issues in a house survey: causes, severity and what buyers need to know

Structural issues in a house cover a range of problems, from cosmetic fractures that need nothing more than filler to serious structural instability that requires an engineer's assessment and may affect your ability to get a mortgage. Understanding the difference is one of the key things a house survey helps buyers do.

Some of the most obvious signs are the fractures found in walls, ceilings and around door and window frames. While these can cause significant alarm, many are entirely benign. Others will require investigation and remedial work. The key is knowing which is which. For an overview of all issues a survey can flag, see our common survey problems guide.

Here, Surveyor Local looks at the types of structural damage and how it forms, how severity is assessed, when to involve a structural engineer, what repairs are likely to cost and how structural issues might affect a mortgage.

• Not all wall damage is structural. Hairline fractures under 1mm are generally cosmetic. Those wider than 3mm, particularly diagonal or horizontal ones, warrant closer investigation.
• Surveys use the Building Research Establishment (BRE) six-category system to assess severity, from Category 0 (negligible) to Category 5 (very severe).
• Common causes include settlement, subsidence, heave, wall tie failure and failed or incorrect lintels.
• A Level 2 survey will identify and describe damage and flag whether monitoring or further investigation is needed. A Level 3 survey provides more detailed measurements and likely causes.
• Where damage is serious, the survey will recommend a specialist structural engineer's report.
• Active structural instability will deter most mortgage lenders. Historic, remedied issues are generally mortgageable with the right documentation.

There are five distinct types of structural damage you might notice when viewing a property. Recognising the type helps you understand the likely severity before the survey has even taken place.

Where possible, it is worth monitoring any fracture over time to see whether it worsens, as this can indicate something more fundamental is happening.

Hairline fractures

Any fracture less than 1mm wide is generally considered cosmetic. These are common in plaster and render and are usually the result of normal drying and movement in building materials.

Stepped fractures

Stepped fractures, sometimes called staircase cracks, follow the mortar joints between bricks in a diagonal stair-step pattern through the brickwork. They can indicate differential movement in the structure and are worth having assessed, particularly if they are widening.

Diagonal fractures

A diagonal fracture, especially where it is wider than 3mm and wider at the top than at the bottom, may indicate subsidence. These commonly track toward the corners of windows or door frames, which are the natural points of weakness in a wall. Checking whether the same fracture is visible on both the interior and exterior wall, and whether the relevant door or window still opens freely, helps build the picture.

Horizontal fractures

Like diagonal fractures, a horizontal fracture is a possible indicator of serious foundation issues, particularly where it is wider than 3mm. It is typically accompanied by the wall bowing outward and can indicate heave or wall tie failure, which may also cause visible damage to the brickwork.

Displacement cracks

Displacement occurs when diagonal or horizontal fractures deteriorate to the point where one side is pushed out or set further back than the other. This indicates active movement and should be treated as a priority concern.

There are several causes of structural damage in a building. Some are benign, others require immediate attention.

Settlement - new-build houses, extensions and other construction projects will naturally settle over time. This often results in hairline fractures and is an expected part of the process, usually remedied with filler and redecoration.

Subsidence - the most familiar cause of serious structural damage. Diagonal fractures typically appear near the corners of window and door frames, indicating significant downward movement of the building. This is usually caused by clay earth drying out and creating a void beneath the foundations, or by root systems from nearby trees drawing moisture from the ground. Poorly maintained drainage can also create the conditions for subsidence.

Heave - related to subsidence but with the opposite effect. Ground under hydrostatic pressure expands and pushes upward on the foundations, causing walls above to bow and fracture horizontally. It is particularly associated with properties where nearby trees have been removed, allowing the earth to rehydrate and swell.

Wall tie failure - in cavity wall construction, metal ties connect the inner and outer leaves of brickwork. If these corrode and fail, the outer leaf can pull away from the structure and begin to bow outward. The remedy is to install new ties, but left unaddressed the structural damage is significant.

Incorrect or failed lintels - a lintel spans the top of a door or window opening, carrying the load of the wall and the roof structure above. If the lintel is under-specified for the load it must carry, is incorrectly installed or fails over time, the weight bears down and causes structural damage. Load-bearing walls typically use concrete or steel lintels; internal walls may use timber.

The survey covers all fractures around the structure to assess severity and advise on next steps. Assessment covers four areas:

Width, depth and length - 3mm is the general threshold. Any fracture wider than this is a potential indicator of something structural that warrants further consideration.

Location - vertical and hairline fractures are generally cosmetic and can usually be traced back to drying building materials. Diagonal and horizontal fractures are more likely to indicate an underlying structural issue.

Monitoring movement - specialist tools may be used to establish whether a fracture is active (still moving) or inactive (stable). This is important for determining the urgency of any remedial action.

Context - structural damage on its own may not tell the whole story. The survey will look for secondary evidence such as damp, sloping floors, gaps beneath skirting boards, sticking doors and windows or disrupted hard standing outside the property.

The BRE crack severity categories

The Building Research Establishment (BRE) six-category system is used to classify severity:

A Level 2 survey will identify and describe cracks, note whether monitoring or further investigation is recommended, and flag any that are cause for concern. A Level 3 survey provides more detail, including measurements and likely causes, so that remedial action can be taken quickly. For any crack the surveyor considers serious, a structural engineer's report will be recommended.

Not sure which survey is right for your property?  Compare RICS surveys.

The survey will guide you on when a structural engineer is needed, but as a general rule you should consider one if:

• Fractures are more than 3mm to 5mm wide
• The fracture is wider at the top than at the bottom
• Diagonal or horizontal fractures are present, particularly if they appear to be widening

The structural engineer will carry out a detailed investigation, prepare a report of their findings and set out the recommended remedial action. Their role is to assess the safety and stability of the building and establish what steps are needed to bring it to a satisfactory condition.

Costs depend on the severity of the problem, how much of the building is affected and the ease of access. Location plays a role too, with London and the South East typically attracting higher labour costs.

Structural engineer's report - typically £300 to £1,000, though this can be higher for larger or more complex properties.

Underpinning (subsidence or heave) - concrete underpinning typically costs £1,500 at the lower end and can exceed £50,000 for a major problem across a large property. Resin injection, a faster and less invasive alternative, is typically £3,000 to £16,000.

Crack stitching and structural movement repairs - minor repairs typically cost £500 to £1,200. Crack stitching, which binds the sides of a crack using iron rods, costs around £1,200 to £3,000 per wall.

Lintel replacement - typically £1,000 to £4,000 or more depending on location, severity and materials.

Wall tie replacement - broadly similar to lintel replacement, depending on the extent of the failure and accessibility.

Concrete repairs - from around £1,500 for a simple patch, rising considerably depending on the scope of the problem.

Always obtain at least three quotes from reputable specialists before committing to any remedial works.

If fractures are minor or cosmetic, they will not affect a mortgage application.

Where damage is more serious and indicates structural instability, lenders become increasingly reluctant to lend. The key distinction is between historic and active issues.

Historic issues - where structural problems have been previously identified and professionally resolved, most lenders will consider a mortgage application. They will typically require a structural engineer's report, a certificate of structural adequacy and evidence of current buildings insurance.

Active issues - where movement is ongoing and unremedied, most lenders will not offer a mortgage until the problem is resolved. These properties occasionally come to market at auction.

For buildings insurance, active and unremedied structural damage makes cover difficult to obtain. Even properties with a history of movement can attract higher premiums or restricted cover. A specialist insurance broker is worth consulting if you have any concerns about the insurability of a property you are considering. Damp resulting from unresolved structural damage can also complicate cover further.

A RICS Level 2 or Level 3 survey is the right first step for any property purchase. Get a free quote or call our friendly team on .