If your house is cracking up it could be in need of therapy
to make good. In older buildings hairline cracks can appear around June to September but then close up in the winter when the building fabric absorbs moisture. These are generally harmless and are called “summer cracks”.
It is more likely that subsidence is taking place. This is more serious and occurs when the ground beneath the house is literally unable to support the load. The shrinkage results in both horizontal and vertical ground movements. Although there are several causes, subsidence occurs most frequently in areas of clay, particularly when there are trees close to buildings. In normal circumstances the moisture content of the ground at deeper levels remains fairly constant. However, during extended dry periods the trees remove water from the soil allowing the clay to shrink, causing foundations to sink. This results in cracking, which when severe, can be seen from both inside and outside. It is particularly apparent in the weak points of the building structure such as between the ground and upper floor windows. The cracks are wider than those attributable to settlement and are generally wider at the top.The impact of mine workings on the integrity of supporting ground is well documented in the Yorkshire area but subsidence also occurs when drains or culverts collapse. The presence of rotting organic material can also destabilise all or part of a foundation. It is important to get the advice of a structural engineer who can monitor the extent of cracking over a period of time and provide the best solution for you. At it’s simplest you may have to do very little other than some minor repointing. If it is serious then some form of underpinning will be required.
Unfortunately this will be expensive and can require the excavation of trenches, approximately 1m in length and 1.5 mdeep, every other metre along the affected section of wall indenting beneath the existing foundation. Steel reinforcement bars are inserted at 90 degree angles into the side walls of the trenches before they are backfilled with concrete. This process is then repeated along the intervening sections creating a single homogenous foundation. It’s a labour intensive exercise and may easily cost £1,000 per linear metre. However, subject to circumstances there are other options available. Pressure grouting beneath the foundation by injecting chemicals effectively turns the subsoil into an aggregate, thereby consolidating the ground. Although favoured by insurance companies because it is significantly cheaper it’s largely ineffective in clay soils with a low porosity.
I would also urge you to consider the removal of any trees planted close to the house. Non indigenous species such as Eucalyptus are particularly damaging and can also disrupt services coming into the house.