Sixteen years ago I moved into this house and the small front garden was
covered over in red tiles. On learning that there was substantial hardcore
under the tiles I decided not to dig them up, so I heaped about 18 to 20
inches of soil *on top* of the tiles.

I then planted this pine tree in the photo, (see tinypic link) believing
that the roots would merely travel along *on top* of the tiles.

http://tinypic.com/view.php?pic=651wgg&s=5

Recently a tree man knocked at the door and said he thought that almost
certainly the roots have found there way downwards through the tiles. If
this is the case I'm worried about the house foundations since the tree is
so very near the front wall.

Would anyone kindly explain to a complete novice what would be the basic
steps I should now take in dealing with this tree which might be a serious
threat to the house. Thanks.