My clients were in the process of selling their house. The buyer needed a mortgage and the Surveyor acting for the mortgage provider had identified evidence to indicate that there has been some structural movement in the house. As such, the mortgage provider took the view that they would not lend any money until a Structural Engineer had carried out a structural inspection and prepared an Engineers Report which would identify the cause of the movement and would make recommendations to return the house to a structurally safe and stable condition.
The property was a 2 bedroom semi detached house that had been built in the 1980s. The general area was reasonably flat and level and there was a large Pine tree about 6 metres from the front left hand corner of the house. The underlying subsoil was a sandy gravelly clay overlying the more predominant London Clay. This type of subsoil has an inherent plasticity and is well documented for its ability to shrink and swell as a direct consequence of variations in moisture content. The moisture content of the clay can be affected by seasonal changes or by forced moisture extraction by tree root systems. The bearing capacity of such soils can also be significantly reduced by abnormal quantities of water entering the ground. Underground services such as drains and water supply pipes that are not completely watertight can sometimes affect the soil in this way.
It was clear that the property had been maintained to a good standard although there was a good deal of crack damage that was consistent with the effects of differential foundation movement below the front left hand corner of the house i.e. the corner nearest the Pine tree. Without a doubt, remedial works were required although the form that they should take could not be assessed until the precise cause of the damage had been fully addressed. For example, if the movement was due to moisture extraction by the tree roots, removing the tree might be an appropriate solution. However, there was also the possibility that removing the tree might cause other problems such as clay heave which is when the clay subsoil expands. I felt therefore that it would be more appropriate to underpin the foundations i.e. to extend the foundations to a depth below the of the tree roots.
I advised the clients that the matter should be referred to their Building Insurers as soon as possible. This was duly done and the insurers carried out their own independent investigations which proved the damage was a result of moisture extraction by the tree roots. Insurers accepted the claim and took the view that removing the tree was the most appropriate course of action. They arranged for the tree to be removed and for the crack damage to be closely monitored for 12 months to check that its removal would have the desired affect. On the basis that the cracking stabilised in due course, they agreed that the damage would be repaired and that the house be redecorated in order to return it to the condition it was in before the damage occurred.
The buyer was not deterred by this course of action and agreed to proceed with the purchase on the understanding that insurers continued to provide subsidence cover for the house.
This case study shows that if a buyer is really keen on a house, the presence of structural damage does not necessarily mean the sale falls through.
