In a mission involving the implication of a legal expert, the owner appointed the architect, engineer and contractor to help with the problem of the increasing subsidence of a semi-detached house. Luc Hens the managing director of ARCON was appointed as the legal expert.


After analysing all the elements in the file, the architectural plans, the plans for the concrete and the specifications, it was concluded that the file complied completely with regulations.

After studying the report on the pre-tests that pointed to ground that was very weak down to 10 metres, the engineer decided for a double reinforced concrete foundation 30 cm deep with a beam to act as a spine extending to a depth of 80 centimetres. The building was built with a strong concrete skeleton structure.  





When measuring the slopes and the levels of the sinking building it was observed that the house leaned towards the back and away from the adjoining house.

After a period of observation it was also noted that the subsidence was continuing unabated and that there was no chance that it would stabilise.

A local site visit and observations led to the realisation that the work carried out when building the house was of excellent quality and that there were no indications of errors in the building works. The cause of the problem was very likely external therefore. 




On inspection it seemed that the adjoining semi-detached house was built on piles and when checking the photos at the beginning of the building works it was possible to see that the partition wall was supported by a heavy partitioning beam on top of the pile heads .

The low-resistance layer of ground was just 10 centimetres thick was probably a levelling layer.

The additional load of the house simply crushed this layer and caused it to compact.  The subsidence can expect from this is enormous.

On the photos one can see that the foundations of the house, at the level of the pile heads along the road, touch the partition beam of the adjoining house.  The difference in the techniques used for the foundations, meant that the subsidence of the adjoining house is negligible because the load is transferred by the piles to the supporting layer ten metres below. The building with the problem connects to the foundations of the healthy building, which explains the slope towards the back.


The building needed deep foundations in order to avoid any further subsidence.

Before this could be done however, it was necessary to restore the house to a horizontal angle.

By injecting a highly expansive polyurethane mousse it was possible to straighten the building. But first we carried out a test to make sure it would work. Which it did.

Several specialised contractors were appointed to lift the building to several millimetres higher than the original position. Piles were then injected under high pressure into the ground down to the load bearing level via concrete moulds.

The result was totally satisfactory. The house is horizontal again and now has deep foundations so that there is no further risk of subsidence.


An exceptional result that was obtained thanks to the excellent cooperation between all the different parties involved including architects and contractors and thanks to the fact that the building was exceptionally robust with a perfect foundation plate with reinforced support beams and a strong concrete skeleton structure. Barely any fissures appeared during the whole operation . And the finish of the building remained intact.