The role of a pre-purchase building inspector is to identify defects in the property and make recommendations that will enable the purchaser to make informed decisions about whether to buy this particular property or not. When the building inspector finds significant cracks in the brickwork or rendered surfaces, or other cracks that may appear to the building inspector to be significant, then the purchaser needs to be informed of how significant the cracks appear to be.
Any prolonged drought in Australia causes a significant increase in the incidence of cracked buildings, particularly housing, due to the drying out of foundation soil. Cyclical periods of wet and dry will exacerbate soil movements over the years.
Some typical issues related to cracking in brickwork is discussed in this article.
Brickwork cracking due to trees
Cracking affecting lintels
Cracking in brickwork related to reactive soils
The movement of the footings and foundations is rarely even over the whole of the building site. Therefore, differential movement under different parts of the footings creates stresses in the walls resulting in cracks. Foundations are usually classified as either reactive or nonreactive to changes in their moisture content. Reactive soils are typically soils that have a high clay content.
These types of soils are referred to as plastic soils, expanding and contracting over time as their moisture content increases or decreases. For example, reactive clays may swell and retain moisture when saturated. This can cause severe cracking in brickwork, particularly in older houses with brick footings.
Cracking in brickwork related to trees
Contrary to popular belief, it is rarely the growth or uplift of the tap roots of big trees which damage the footings and foundations. The damage is more often caused by the tree roots extracting considerable quantities of moisture from the soil. This can cause footings and foundations to subside and cracks in the masonry to appear. This phenomenon is known as tree drying settlement.
A commonly accepted formula is that a tree's root system will extend for a horizontal distance equal to its height. A large healthy tree can extract up to 300 litres of moisture from the per day.
Cracking in brickwork related to poor site drainage
The provision of an adequate storm water drainage system to carry all roof water away from the footings and foundations is essential to avoid subsidence, rising damp, cracking and the eventual failure of the structure. Downpipes should be connected to a storm water drainage system or water conservation tank to avoid failure of footing and foundations.
Cracking in brickwork related to lintels
Cracking in brickwork can often be associated with settlement, subsidence, poor drainage, inadequate footings, reactive soils and brick growth. Cracking can also be a result of other forms of destructive processes, such as corroding steel lintels or arch bars.
The expansion of the steel can be destructive to brickwork. We recommend that corroding steel lintels be replaced with galvanised steel to avoid further destruction of the brickwork.
Cracking resulting from brick growth
Fired clay products expand exponentially over time, and it is an inherent phenomenon of all natural clay products fired at relatively high temperatures. This includes most clay bricks, pavers and ceramic (clay) tiles. Much of the growth takes place in the first few months and may become evident as long vertical cracking.
Essential advice to assist in reducing further cracking in brickwork
- Ensure that all downpipes are placed into a storm water drain or water retention tank.
- Keep ground levels at least 3 bricks below the damp course.
- Keep tree roots at least 5 metres from the footings and foundations.
- Replace corroding lintels with galvanised steel.
- Keep mortar joints in good repair