Cracks in the ceiling, cracks in the wall, a damp cellar – building defects are not always responsible. The condition of the building ground can also lead to these problems. To avoid damage and additional costs, this should ideally be checked with a soil survey before the property is purchased, but at the latest before construction begins, advises geologist Günther Weixelberger.
What is a soil survey?
“A soil survey, often also referred to as a subsoil survey, provides information about the nature of the soil,” says Günther Weixelberger, who runs an engineering office for geology in Pitten. The geological situation, materiality, condition and load-bearing capacity of the soil as well as the groundwater level are recorded and analyzed. “Using this data and information, foundation and infiltration concepts can be perfectly adapted to the given conditions during planning and construction and the risk of subsequent damage can be reduced,” says Weixelberger.
What information does a soil survey contain?
These findings can ultimately be found in the report: “It states, for example, whether the soil is loose, medium or dense, loamy, stony or similar,” Weixelberger explains. It also contains information on the depth from which it is stable and whether there is groundwater or stratum water. “If the ground has been backfilled, as is the case with former gravel pits, for example, this is also included in the subsoil report,” explains Weixelberger. It also contains soil parameters – these technical details are important for planners and structural engineers – as well as information on the type of foundation required. In addition, infiltration concepts are an essential part of soil surveys.
How does a soil survey work?
Preparing a soil survey is a complex process. As a rule, data from public databases such as the groundwater or contaminated site register and geological maps are collected and analyzed. This information is usually supplemented by a field investigation on the property. If necessary, samples are taken from excavation trenches at various depths and examined in a laboratory for their physical and possibly also chemical properties, and the strength of the ground and the water level are measured with a probe. The steps required in each individual case depend on the findings of the data analysis and the site inspection as well as the planned development.
Why is a soil survey important before building a house?
“The building site determines how a house should be built,” says Weixelberger. If you don’t know enough about the nature of the ground, it can lead to unpleasant surprises in the short or long term, such as moisture ingress, cracks, subsidence damage or landslides. “This can be the case with your own property, but also with other buildings or traffic routes,” says the geologist.
What happens if you build without a soil survey?
In the best case scenario, you are lucky and nothing happens. Otherwise, however, as just mentioned, serious problems can arise. These are often very difficult to deal with and usually only with considerable additional financial outlay, for example for construction stoppages, soil improvements, slope stabilization measures or the repair of damp walls. However, these are not the only costs that can be incurred if problems arise due to a lack of a soil survey. “The ground risk is borne by the builder,” says Weixelberger. This means that the client must bear all costs incurred in connection with a construction method that is unsuitable for the soil in question. There is also the risk of long-lasting and expensive disputes, whether with planners, construction companies or neighbors. Relying on insurance is of little help in this context: “If damage occurs due to a weak foundation, the insurance will not pay for it,” says the expert.
A soil survey would therefore ensure the stability of buildings and builders. “With a subsoil report, the expert assumes liability for the subsoil risk,” says Weixelberger. On the other hand, it helps to avoid unexpected additional costs during the construction phase and costs for repairing damage.
What does a soil survey cost in Austria?
The cost of a ground survey depends on the amount of work involved. “But you can generally expect to pay around 3,000 euros for a simple soil survey,” says the geologist. An expense that pays off, however: “There is a rule of thumb according to which the cost of rectifying problems that arise during the construction phase due to a lack of a soil survey increases by a factor of ten. This applies even more if they only occur years later,” calculates Weixelberger.
How long does a soil survey take?
Depending on the work involved, a soil survey can take between two to three weeks or several months. The latter is the case, for example, if a drill is requested or samples are analyzed in the laboratory.
Who prepares a soil survey?
A soil survey may only be carried out by authorized offices, i.e. civil engineering, engineering or technical offices.
Is a soil survey mandatory?
Soil surveys are not mandatory at either federal or state level. “However, in some municipalities, such as the Wienerwald municipalities or in alpine areas, they are a prerequisite for construction,” says Weixelberger. Structural engineers and insurance companies are increasingly demanding a professional assessment of the ground conditions.
Our expert
Günther Weixelberger studied geology at the University of Vienna. In 1996, the sworn and court-certified expert founded the engineering firm “Geologie Weixelberger”, which specializes in soil surveys, geotechnics, environmental geology, hydrogeology, seepage, earthworks and hydraulic engineering.
Website: https://www.weixelberger.at/
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