One thing that is almost certain in all buildings around Perth is that there is some form of cracking that has occurred to its building elements. However, not all cracks are an indication of a structural problem. Your home is surrounded by many variables & as such a small amount of movement should be anticipated.
What types of cracks are common to most properties?
All types of cracks should be monitored, however, the following cracks are generally typical to most homes:
Shrinkage Cracks: As building elements dry, shrinkage occurs, creating minor cracking to building elements. These cracks are particularly associated with concrete slabs. These types of cracks should be monitored as they may allow moisture egress & contribute towards spalling of concrete (concrete cancer).
Settlement cracks: Settlement is the downward movement of a building to a point below its original position, which is usually the result of the shifting or compaction of the underlying foundations. Most settlement cracks are the result of short-term settlement. Ongoing movement is unlikely & uncommon, although cracking should still be monitored to ensure this is not the case.
Minor cracking in mortar: Cracking within mortar joints can be the result of shrinkage cracking or differential movement of building elements. For example, minor rusting of lintels or even the expansion or contraction of some building materials in varying weather conditions may all result in minor cracking in mortar. In the instance that cracking in mortar is identified the origin of the cracking should always be identified to ascertain whether the cracking is deemed a structural issue.
What types of cracks are deemed structural?
The majority of structural cracking can usually be attributed to foundation movement or damage. Cracks may be identified in the following forms:
Vertical Cracks: Differential settlement, poor or uneven compaction or soil erosion under foundations are just some of the causes in which vertical cracking may occur.
Angled Cracks: When up and down loads are applied so that the forces are offset from one another, cracks are likely to occur at an angle. This form of cracking is generally associated in areas with reactive soils.
Horizontal Cracks: This form of cracking is generally found along the mortar joints of brickwork, in areas where the brickwork is visibly out of plumb. Deflection of the footings may have occurred or the brickwork may not be able to support the load placed upon it.
Diagonal Cracks: As opposed to a step crack that follows the mortar, these cracks ‘tear’ through the building element. This form of cracking is almost always associated with structural foundation movement.
How is structural cracking assessed?
Cracking will be assessed as part of a building inspection, however if a category 3 crack or greater is identified a structural engineer should be immediately consulted. Cracking is categorised into the following 5 categories with a description of typical damage and required repairs:
- 0 – Hairline cracking, under 0.1mm,
- 1 – Fine cracks that do not need repair, less than 1.0mm,
- 2 – Noticable cracks, yet easily filled 1.0mm -5.0mm,
- 3 – Cracks that can be repaired and possibly some of the wall sections will need to be replaced. Note weather tightness can be impaired, 5.0mm – 15.0mm,
- 4 – Extensive repair works required involving breaking out and replacing these sections. Walls can become out of plumb and fall and causes reduced bearing capacity, 15.0mm -25.0mm.
What causes structural cracking?
Common causes of structural cracking to building elements may include:
Trees in close proximity to foundations: Root systems may damage footings directly or attribute towards moisture variation of soils, & in both cases structural cracking may occur.
Soil Moisture Content: Inadequate drainage to a property increases the likelihood of structural cracking; see here for further information on diverting surface & storm water away from your property.
Uneven foundation settlement: Varying soil properties on the same site or inadequately compacted fill are just two examples of uneven foundation settlement. Where possible compaction certificates should be obtained if you are building a home.
What can I do to reduce the likelihood of structural cracking?
Ongoing consideration should be given to your home & efforts should be made to control the moisture content of the soil in close proximity to your homes foundations. Care should be taken when landscaping to choose suitable vegetation & reticulation systems should not be used directly against a property.
Can I take action against my builder if I identify structural cracking?
For residential home owners considering negligence action against their engineer, classifier or builder they should be aware of the performance criteria in the AS2870 which acknowledges the risk of significant cracking to a small number of houses. If the engineer, classifier and builder have all acted in good faith, they are well protected by the code.
It is always best to seek independent advice from a suitably qualified person prior to consideration of legal action.