On Saturday, May 31, 2014 10:03:38 AM UTC-4, wrote:
Is it OK to drill round holes in the flooring where house wiring crosses the joists so that there is no pressure on the wires at those points?

Between the joists the wires would be pushed slightly below the flooring.

Thank you for advice.

I might also install protective metal plates over each of the holes.
Not only does this prevent accidental damage to the wiring but it also locates all the wiring on the floor of the attic. I would fasten both the 4x4's and the metal plates with screws for easy access.