Without x-ray glasses, our inspectors can't tell the exact thickness of the basement floor. The best way to get a close estimate is to measure the bottom block in the wall. These blocks are 8 inches tall. If he can see more than 4 inches above ground, he knows that it isn't safe to install a below ground drainage pipe system. If he can't see the wall because the basement is finished, he will look for a closet or utility room like this picture shows.