Subsidence – What to Do if You Notice Cracks in Your Walls

example of subsidence

Cracks in walls, ceilings, flooring or around doors and windows may occur for several reasons. Many cracks are cosmetic and are not serious. However, some cracks may be the result of serious structural problems.

If the ground under a building shifts, shrinks or swells, this movement may cause cracks to appear.

Subsidence can occur because of changes in moisture or temperature. It can also occur because of the ground compressing under the load of the building.

Most homes settle a bit after they are built. However, too much settling may be the result of a poor footing system. The building may settle unevenly or sink too much. Although it may be possible to construct a building with a footing system that does not allow subsidence, to do so can be extremely costly.

Most building codes allow a certain level of subsidence. The Building Code of Australia has defined tolerance levels that apply to how a slab and footing must be designed and constructed.

How to Know if Cracks Are Serious

The BCA provides guidelines to determine when cracks may indicate serious problems. Hairline cracks in walls, cracks that are less than 5 mm wide or those that can be easily filled and are less than 5 mm wide are within the normal range.

Bulging walls or cracks wider than 5 mm that cannot be repaired without replacing the wall do not fall within the tolerance level.

Doors and windows may stick for many reasons. Usually, a homeowner is responsible for routine maintenance. However, if doors and windows are difficult to open and close, have gaps around the frames or look uneven, there may be a problem with subsidence.

Hairline cracks in concrete floors that are less than 2 mm wide are not usually a cause for concern. Sometimes a slab will settle and cause a change in level. There are accepted norms for this change.

You can test whether settlement of your slab exceeds this norm. Centre a 3-metre straightedge over the crack. If there is a deviation in level of more than 15 mm, then the deviation does not meet BCA standards.

Changes in slope that exceed 1/100 do not meet standards. If you notice that floors, ceilings or joins sag or slope, chances are there is too much deviation in slope.

How to Rectify Cracks That Do Not Meet BCA Standards

Cracks that fall within the normal range are the responsibility of the homeowner to repair. If you have cracks that do not meet standards, there are several ways to proceed.

If your home is less than 6 ½ years old, your home may still be under warranty. Your building contractor may be responsible for rectifying these problems. First, contact the builder and describe the problem.

If the builder does not accept responsibility, you can contact the Queensland Building and Construction Commission. QBCC will request a site inspection to investigate your complaint.

Elements of a Site Inspection

The site inspector will examine the building and external areas of the property to determine whether the building contractor has complied with BCA construction standards. The builder and the homeowner will be invited to be present during the inspection.

The inspector will look at expansion joints throughout the property, including in masonry, internal walls, plumbing and external drainage systems.

The inspector will look at how well the home has been maintained. Leaking taps, blocked downspouts and clogged guttering will be noted. In addition, any changes made after the home was occupied will also be noted. The inspector will also examine site drainage patterns, evidence of standing water, tree roots that affect drainage and broken pipes.

Finally, the inspector will record the extent of damage from movement, including doors and windows that stick, cracks in walls or floors or other visible evidence of subsidence. A floor plan will show floor levels to evaluate changes in slope.

Post-Inspection Assessment

The inspector will determine whether the subsidence and movement are within the normal range as set out in BCA standards. The inspector may also request a plumbing check to look for broken pipes or hidden leaks.

If the problems are the result of defective construction, the builder may be asked to correct them. If the problems are due to poor maintenance or alterations made by the owner, the owner will be responsible for rectification.

If the inspection cannot determine the cause of the problem, a specialist will be called by QBCC to investigate. The specialist will continue the investigation to identify the source of the problem and provide a solution.