I have planning permission for a garage and study to be built on to the side of the house. To save money, I have taken on digging the footings myself, by hand. My problem is that the 1930's house is built upon the site of an old victorian refuse tip. To reach firm ground I had to dig an exploratory hole to a depth of 7 feet. I am worried that by excavating to this depth around one side of the house I may undermine its foundations a cause a collapse. Am I best to leave this type of excavation to the experts or do you reckon am I safe to proceed on my own.