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What is subsidence?

Subsidence is the downward movement of the ground supporting a building. If this movement varies from one part of a building to another, cracks may occur.

Subsidence causes

Causes of subsidence include:

  • soil compressing under the weight of the house
  • soil swelling and contracting due to changes in the moisture content.

Subsidence and footing design

In Queensland, engineers design footings to the Australian Standard AS2870 – 2011 Residential slabs and footings. Footing design and construction involves a number of steps:

  • site classification
  • selecting the footing system
  • structural design
  • building in accordance with the required design details and methods
  • proper maintenance.

Choosing appropriate site falls and floor levels should be part of the planning and setting out process during the construction of a new home or renovation. Where abnormal sites or environmental conditions exist, get advice from a qualified Registered Professional Engineer about the installation of an appropriate footing system.

Preventing subsidence

  • Maintain site drainage
  • Avoid:
    • altering the site drainage provided by the builder. Any drainage changes should direct water away from your house and adjoining properties
    • placing gardens, garden edging or gravel pavements next to your house. These can cause water retention or may change the moisture conditions, particularly on reactive clay sites
    • installing a sprinkler system next to your house if it is on a highly and extremely reactive site
    • over watering
  • Plant trees around your house at a distance greater than the fully-grown height of the tree
  • Regularly check and maintain plumbing, drainage and stormwater systems. Immediately repair leaks as well as minor damage and cracking in walls and ceilings.

More Information

A Simple 'How To' Guide to Preventing Structural Damage to Your Home

Homeowners Guide to Subsidence

Licence
Creative Commons Attribution 3.0 Australia (CC BY 3.0)
Last updated
11/10/2013 1:40 PM

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