YOU NEED TO ASSES THE SITE PROPERLY
When you break open the ground to dig foundations for a house you can never be 100% sure about what you are going to find. If you are lucky, you will come across nothing but good load bearing sub-soil and your foundations may proceed with great speed and little cost. But there are many things that can conspire against you. Principal amongst these are difficult ground conditions that require something more elaborate than simple trenched foundations. Other possible problems include archeological remains or sewers, or electricity cables.There are two approaches to this risk. One is the cautious one, that involves making as many investigations as possible beforehand often this involves considerable expense in itself. Cautious builders dig trial holes and have them inspected by structural engineers who write reports recommending certain courses of action.The other approach is more cavalier - don't worry about the foundations until you open up the ground. In theory, the cavalier approach shouldn't cost you any more - in fact it will save you the investigation costs. But in practice, if you are unlucky and you meet problems, it is likely to delay progress substantially and in an unplanned way. This is a cost in itself.