Cracking In Buildings

Cracking is a relatively common feature in all buildings, regardless of age or form of construction. Types and severity of cracking vary widely from cracking in non-structural finishes due to drying and shrinkage of material up to more severe forms which have a destabilising effect on the building structure. This article focuses on cracking which may be experienced in masonry buildings typically found in residential construction or other low-rise buildings.

Building owners and operators commonly engage the services of a structural engineer to carry out building condition surveys where there is some reason to get a professional view on the condition of that building. On inspection of a building, an engineer will look to first get an overview of the form of construction and identify key load-paths. In the case of a masonry frame building, vertical load from the roof will be transferred to load bearing walls and into the ground at foundation level, with roof, wall and floor elements tied together to provide overall stability. The engineer will then review load bearing elements where possible to assess any damage or potential issues with the original load-paths. In the case of masonry buildings, cracking may be evident in walls both internally and externally and the nature of these cracks will be recorded for future review at this time.

Aesthetic

• Hairline cracking to internal plaster
• Cracked floor finish
• Damage categories of 0, 1, 2 (crack widths typically 0 – 5mm)

Serviceability

• Rainwater ingress
• Doors sticking
• Damage categories of 3, 4 (crack widths typically 5 – 25mm)

Stability

• Loss of bearing at lintel
• Progressive foundation subsidence
• Damage category 5 (crack widths in excess of 25mm)

Aesthetic damage is caused for example when cracking is experienced in finishes such as paint or tiling and which will not have any material impact on the building. Serviceability damage is slightly more significant in that movement in the building may lead to doors sticking or water penetrating walls.   While they will not impact on the structural stability of the building, they will either have a negative impact on building users or will lead to long term deterioration which will eventually be significant, if not addressed. Finally, stability damage can occur for example where cracking results in loss of buttressing to external walls or loss of bearing at a window lintel. These are issues which require short term intervention due to an unacceptable risk to the safety of those in or around the building

‘Severe’ damage cracking of width circa 15mm, with pattern suggesting differential movement of walls and resulting loss in stability

As crack width is a strong indicator of damage and risk, this is something that is often used by an experienced engineer to determine underlaying causes and prepare strategies for remedial works. Taking each of the types of cracking identified, it is possible to further differentiate cracking in terms of damage on a scale of 0 (‘hairline’ cracking to 0.1mm in width) to 5 (‘very severe’ cracking in excess of 25mm). Another very useful indicator is cracking pattern, which can assist in understanding the underlying causes. An image is provided here, taken from BRE Digest 251, which shows some typical patterns resulting from movement in the foundations of a building.

Crack patterns resulting from Foundation Movement

Taking the crack width, pattern and other factors such as location and age, it is possible for an experienced engineer to form a view as to the likely cause of the cracking and to form a strategy for any remedial works required.

Depending on the severity of cracking, a number of remedial measures are available to building owners. In terms of serviceability level damage, particularly in the case of external cracking, it is advisable to ensure that water ingress to the building walls is avoided. In these cases, a suitable approach may include locally removing the render before injecting the crack with a low viscosity epoxy resin and re-applying render reinforced with an expanded aluminium mesh. For cracks which are severe, and which have a destabilising effect, repair can take the form of crack-stitching. This typically consists of chasing mortar joints into the wall each side of the crack at specified spacings and depths in order to insert stainless steel helical stitching rods before making good the mortar. An image is included for reference. In most cases, damage can be limited by early identification and intervention, preventing ongoing degradation and saving cost to the building owner.

Depending on the severity of cracking, a number of remedial measures are available to building owners. In terms of serviceability level damage, particularly in the case of external cracking, it is advisable to ensure that water ingress to the building walls is avoided. In these cases, a suitable approach may include locally removing the render before injecting the crack with a low viscosity epoxy resin and re-applying render reinforced with an expanded aluminium mesh. For cracks which are severe, and which have a destabilising effect, repair can take the form of crack-stitching. This typically consists of chasing mortar joints into the wall each side of the crack at specified spacings and depths in order to insert stainless steel helical stitching rods before making good the mortar. An image is included for reference. In most cases, damage can be limited by early identification and intervention, preventing ongoing degradation and saving cost to the building owner.

Proprietary helical bars chased and resin fixed into mortar bedding

The ORS Civil and Structural Team regularly undertakes structural condition surveys for a large range of clients. Our experience and track record of delivering comprehensive surveys and reports in a quick turnaround time, guarantees client satisfaction and regularly results in repeat business.

If you have a requirement for a structural condition survey due to prominent cracking or other defect please get in touch with Mark Heslin (Civil and Structural Team Leader) or Alan Kenna (Senior Chartered Structural Engineer) who will be happy to discuss your requirements.