I work in mainly new highrise construction. Typical floors are 190mm (approx 7-1/2") and having to chip a shallow trench in the ceiling or floor (to bury BX cable or 1/2" ENT) has not been an issue with the engineers or inspectors so long as the steel isn't cut. Usually we don't have to go deeper than 1" or so, unless there's a spot where the rebar is too shallow and we have to go behind it.
Check with YOUR engineer first though
[This message has been edited by u2slow (edited 02-21-2004).]