we plan to lay ceramic tile in a particular room (an addition to the
house). we've got the tile, we've got 1/4" backerboard, we've pulled up
the carpets. now i find that the floor is quite uneven in some places. In
particular, there is a vertical drop of about an inch over three
horizontal feet toward one wall. this drop extends the length of the
floor.

presumably this is not acceptable to put tile on. any suggestions? will i
have to build up the floor along that wall?