The Request for Help (Booking an Inspection)
The appraisal and diagnosis of slab heave starts at this early stage and continues until enough information has been collated to discard the theory of slab heave. The other causes of slab movement are:
- Consolidation of loose soils (including uncontrolled fill).
- Subsidence due to adjacent excavations.
- Bearing failure of soft soils (extremely rare).
By the time home-owners call to arrange an assessment of cracks in a building by a structural engineer, they have worried and watched cracks appear in their house for some time. In some cases, where the house has moved and cracks appeared within the builder’s warranty period, the damage may have already been inspected or even repaired by the builder.
Often times, a request for an engineer’s inspection of cracks in a house is therefore preceded by many weeks or perhaps months of the home-owner watch their single largest investment slowly try to destroy itself.
The more technical minded home-owners may have read on forums about slab heave and it’s incidence around the country.
The information available to them at this stage is a dismal picture of house movement leading to possible bankruptcy. They are facing the possibility that their house will become unliveable and have to be demolished and rebuilt at their own cost.
When it comes to movement and damage – perception is everything. If a homeowner can see damage in a house then it is a very real threat. Living with this damage day-by-day, watching cracks grow across a wall or ceiling is very disturbing and can cause friction in a household.
It is your task then, even at this stage, to reassure them. The media does an excellent job of raising awareness of slab heave issues, and there are law firms that are able to manipulate perception and build themselves a workload in the interim, however the process for assessing and diagnosing slab heave must run its course – and house demolition and bankruptcy are rarely, if ever, the solution.
Slab heave is the domain of structural engineers, not lawyers.
When a client rings to arrange an inspection of cracks in their house, do this:
- Reassure the home-owner. Cracks happen in houses. They don’t mean the house is about to collapse. By working with the home-owner you CAN fix the problem.
- Get information.
- How old is the house?
- What style house is it?
- Is it single or double storey?
- Is it on stumps or a concrete slab?
- Where is the house?
- When was the damage first noticed?
- Why is the home-owner concerned?
- Does the home-owner have the original architectural and structural plans for the house?
- Make an appointment. By the time a homeowner speaks to a structural engineer about house damage, they are ready to have the damage inspected. You can not EVER diagnose slab heave over the phone – even if the house is in the middle of a a known slab heave area. You need to inspect the damage and single most helpful thing you can do for a home-owner is reassure them. Houses do not collapse simply because of cracks in walls.
Remind the home-owner that slab heave assessment, diagnosis and repair is a slow process. it is important not to raise the home-owner’s hopes for a quick solution.
If the homeowner is selling, has sold or needs a simple assurance that the house is not ‘falling down’, that inspection and report process will be somewhat truncated and not nearly as detailed or expensive.
Dial Before You Dig
This free service is designed to help identify and protect Australia’s underground infrastructure. It is an awesome, value-adding tool thad I use in just about every slab heave investigation. Identifying the location of major public under ground infrastructure and ruling out its effect on the house is a critical step in identifying the cause of damage to a house. Houses built adjacent to underground infrastructure need to be supported below the zone of influence to protect them from subsidence of unconsolidated trench backfill.
If underground public infrastructure is identified close to the building, consider whether the building is suffering from consolidation of the trench backfill. Look for sideways movement of verandah slabs, depressions in the ground along the trench line, slab levels indicating the slab is tilting towards the trench. If the trench is under the building look for acknowledgement in the design of the trench location, low slab levels along the trench centreline, deflection and rotation of the house around the trench centre line. I these cases, the house is likely to be suffering from consolidation, not slab heave. Eliminate these issues in a typical slab heave investigation by ordering a dial before you dig.
There is also potential for public infrastructure trenches to introduce moisture to the soil under a house. Look for high slab levels adjacent to the trench. This can be confusing on site because the mindset is that trenches adjacent to buildings cause consolidation. Look past this mindset when investigating slab heave I relation to adjacent trenches.