Does anyone know if its ok to add more insulation over an existing floor in a attic that has insulation already under the floor.
adding more insulation to attic
Sure it's fine. More insulation is more insulation, doesn't matter if you've got flooring in between. If you don't intend to use the 'floor' anymore, you might consider having "blown" insulation installed. It's roughly the same cost as buying DIY batts. There's even a fire-retardant treated cellulose (paper) that is a great insulation and you don't have to worry about getting it on you if you need to go into the attic. (no "itchies")
I agree with the pirate. More insulation isnt a bad thing. There is a point of diminishing returns though :-)
daugenet is certainly correct, however in zone 5a, it takes a lot to get to that point.