Before you buy a site, it is recommended that you have a thorough site investigation carried out by a site investigation specialist and employ an engineer. The engineer can then design foundations which are appropriate based on the findings of the site investigation.
The engineer that is appointed must be qualified by examination, possess professional indemnity insurance, and be in private practice. The engineer's report could result in it making more sense for the builder to use the site differently by avoiding hazards and rearranging the site;
For example:
If your original house location was on the site of an old pond - then it is best to relocate the position of the house.
