Hi, I had a double storey extension built over a year ago. The floor used for the 1st floor is 18mm or 25mm chipboard (ok, its cr@p), this is nailed to very large joists supported by an RSJ one side and hangers the other. This was all approved by the building regs inspector. The 1st floor floor is now approx 1/4" lower than when it was built!!!!! There are 1/4" gaps under the architrave. The bathroom tiles not longer touch the tiles bathroom floor by 1/4". The new floor is now 1/4" lower that the old floor!!!! There are no cracks either upstatirs or downstiars!!! I'm gonna get the builder back, but any ideas what is going on here?? Cheers, Matt.