As you may well be aware (especially with the recent hot weather we’ve had) during dry summers the ground can shrink. This is due to the moisture change in the soil, particularly those with a high clay content.
This shrinkage can affect structures such as buildings or walls and cause subsidence. Many new structures are designed with this in mind with foundations that bear deep enough into the ground to remain unaffected. Minimum depths are specified in the NHBC technical guidance and, as an example, in the Bristol area when in a highly shrinkable clay area, foundations should bear at least 0.9m below existing ground level. This may need to increase when factoring in nearby proposed or existing trees.
Older buildings with shallower foundations are more likely to be affected and some will develop cracks which may well open and close dependant on the time of year and moisture content of the ground. Normally if these are of concern, a suitably qualified Engineer will be asked to review and advise upon the next steps such as monitoring and investigation.