Cosmetic House Cracks or Subsidence?

Why do you see cracks in your home? How can Structural Engineers help?

The most common reasons for cracks based on our experience with over 1000 building inspections and 4000 projects are:

  • cosmetic plaster cracks
  • lack of external leaf lintels
  • historic settlement
  • thermal movement
  • drainage leaks
  • moisture infiltration and poor ventilation
  • lack of movement joints
  • poor workmanship
  • local overloading
  • slope stability (foundation sliding)
  • clay soil and proximity of trees

Why do house cracks need assessment?

When cracks, uneven floors, bowing walls or other structural defects are observed by a building surveyor or mortgage valuators, they require inspection by a Chartered Structural Engineer. Very often, small thermal and minor historic settlement defects affect the valuation of properties, and many buyers pull out once they see a conservative survey report that might negatively present the condition of a building due to the cracks observed.

The assessment of cracks by a Structural Engineer might also be affected by the experience of such an engineer. Some Structural Engineers might be very conservative and report that small hairline cracks are due to subsidence, which results in difficulties in obtaining mortgages, and valuations of properties are negatively impacted by such assessments.

Generally speaking, only a small percentage of properties require significant structural repairs, and most of these issues could be repaired without incurring significant costs.

Sometimes, homeowners report minor cracks to insurance companies to obtain repair funds. In many cases, this process takes years without any payments and only increases insurance premiums. Insurance claims, even when no compensation is paid, might be a stressful experience and can impact the valuation and marketability of these properties.

Why do wall cracks need assessment?

When cracks are initially observed, it is important to assess to determine if there are structural defects or if minor maintenance repairs are only needed to prevent or minimise the reappearance.

How can these cracks or subsidence be repaired?

Proper plaster repair with skimming mesh, installation of flexible decorating sealants where required, or local re-plastering can address thermal movement and defects in workmanship. For larger cracks between 3 – 5mm, helical 6mm metal bars such as those supplied by Helifix or Twistfix bars could be used to strengthen masonry walls locally. However, it is critical to identify why the cracks appear, as installing helical metal bars in areas with active foundation movement might result in greater damage.

For buildings with active foundation movement, underpinning, piling or ground improvement might be required. Traditional mass concrete underpinning or piling is the most effective solution in areas with large trees and highly cohesive soils. In other cases, less invasive solutions, such as ground injections with geopolymers, might be better than traditional underpinning. It should be noted that, regardless of whether it is underpinning or ground improvement, in some cases, these repairs are driven by non-technical sales professionals’ targets and are unnecessary or done incorrectly with very limited technical input. Some warranties provided might be unenforceable in case of further foundation movement and not useful when re-mortgaging or selling the property.

In summary, regardless of defects and repair methods, the process requires reasonable assessment by an experienced Chartered Engineer with extensive experience with building inspections. The scope of the repairs needs to be properly considered. In many cases, simple maintenance or limited local repairs are sufficient to prevent significant issues with obtaining mortgages, re-mortgaging, and undervaluing homes when selling.

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