All residential buildings have a natural tendency to move. This movement (which can be upwards, downwards or rotational) will often result in cracks and is generally caused by problems associated with the foundation and will vary based on the soil type.
How is this relevant to a home owner? Well, it is important that homeowners identify the soil type in order to apply certain measures which can prevent costly problems. Must issues are encountered on clay soils and the amount of swell and shrinkage will vary.
The Australian Standard 2870-2011 - residential slabs and footings sets out the criteria for the classification of a site and the design and construction of a residential footing system. It is very important that even “small” structures such as screen walls, sheds, granny flats and retaining walls equal or greater to 500mm are designed and constructed in accordance with the this standard (and others which may apply).
The soil classification for a particular residence may be obtained upon enquiry to the local authority with a good degree of reliability. For all new structures a soil classification or geotechnical report should be commissioned.
How to prevent cracking in my home? Assuming that the home is well designed and constructed, one of the most common causes of cracking is due to trees or shrubs that are allowed to grow in the proximity of footings. The tree roots may effectively lift the footings thus causing movement and cracks. The roots can also absorb moisture in the foundation soil which can cause shrinkage and subsidence.
Another common problem is encountered when a service pipe such as a stormwater drainage pipe contains a water leak which subsequently causes erosion. A leaking tap near a building can have a similar effect particularly in clay sites. Poorly designed roof pluming, incorrect falls in roof guttering, corroded gutters may also direct a concentration of water directly adjacent to footings.
The CSIRO has published Building Technology File No 18 which in our view is a good source of information for all homeowners. For technical advice regarding new foundations, building inspections or to discuss existing cracks which are of concern, contact RBC. (photo courtesy of thetreecenter.com)
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