Bouncy floor in new extension

[lostlalaloopsy]

We are building a 2 storey extension. Plasterboard has gone on downstairs and upstairs is partially floored. We've noticed there is a bounce on the upstairs floor, it makes the downstairs ceiling move and is affecting the new lights etc. Has anyone any experience of this? Or have any suggestions? The joiner has not been very helpful!!

sounds to me like the joists are undersized, or perhaps they have been notched by a plumber with a chainsaw.

1. look at your plans to see what the depth and spacing of the joists was meant to be

2. find out if it was built that way. You can measure spacing by looking at the distance between the rows of nails. Depth if it is partially floored you can measure, otherwise may be more difficult unless you can see the thickness of the floor from a stairwell or something. A ply floor, screwed tightly down, adds a bit of rigidity. Chipboard, not so much, but you can replace it with ply in a few years when it cracks.