Foundation maintenance: a summary of the CSIRO guide
A guide for homeowners. Why houses move, what to look for, and how to look after the ground around your home.
The CSIRO publishes a short homeowner’s guide called Foundation Maintenance and Footing Performance. It explains why houses move with the soil beneath them and what owners can do to limit cracking. Engineers and builders across Australia hand it to clients, and many people know it by its earlier name, BTF 18. This page summarises the main points. The full four page guide can be downloaded below.
Why houses move
Most movement starts in the soil. Clay soils swell as they take in water and shrink as they dry, and this happens unevenly around a house, so one part of the footing moves more than another. The guide describes the main causes:
- Settlement after construction, usually in the first months.
- Erosion, where water washes soil away from beside or beneath footings.
- Saturation, where clay becomes so wet it loses its strength.
- Seasonal swelling and shrinkage of clay through wet and dry periods.
- Tree roots, which dry out the soil and can also push up on footings.
What you may notice
- Cracks in walls, most often near doors and windows.
- Doors and windows that start to stick.
- Cracks at cornices and floors that dish or dome slightly.
The guide notes that most cracking in masonry walls is cosmetic. It includes a table from the Australian Standard that grades damage from hairline cracks through to severe, which helps you judge when a crack needs attention. Cracks should be monitored, and cracks that keep growing should be looked at by an engineer.
How to look after your foundations
- Fix leaks. A small leak from a pipe, drain or tap near the house can be enough to affect clay soil.
- Maintain gutters and downpipes. Keep them clear, and make sure downpipes are connected to the stormwater system.
- Drain surface water away. Check where water flows during heavy rain and direct it away from the house.
- Protect the perimeter. The guide recommends paving around the house that falls away from the walls.
- Plan the garden. Keep plants that need little water closest to the house, and place thirstier plants, shrubs and trees further out. Avoid overwatering.
- Take care with trees. Get advice before planting large trees near the house or removing established ones.
- Ventilate the subfloor in houses with timber floors on stumps or piers.
- Do not dig beside footings without engineering advice.
Download the full guide
Foundation Maintenance and Footing Performance (PDF, 4 pages)
Foundation Maintenance and Footing Performance © Commonwealth Scientific and Industrial Research Organisation (CSIRO) 2024, licensed under CC BY-NC-ND 4.0. The guide is reproduced here unchanged and is also available from the CSIRO Building Technology Resources page. The summary above is ENGPRO’s own and is general information only. Seek advice for your particular site.
Related: What is a waffle slab?
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