I wouldn't worry about it. We have out workout room on the third floor of our house. The room is similar to a loft. In this room we have weights in 5 lb increments, from 5 to 95 lbs. And yes, they all get used ~ not just by me ~ haha. We also have a treadmill and a Body Solid Gym (sqat rack and other things), and a leg press (gym quality), in addition to other smaller essentials, tv, stereo, step(s) etc. We do have some cracks in the ceilings down stairs and the trim around some door frames are separating a bit, but it's worth it! I worried at first too, but so far so good.
Susan C.M.