Over the Summer (July 2016) I lifted old carpet and flooring and insulated between the joists (kingspan) and put another layer of plywood before laying solid wood flooring in a bedroom.

Over the last few months, the old flooring in the hallway, which is laminate has started to become very springy and now I have noticed that one wall joining to the other side of the wall in the bedroom - where the new flooring was laid has a 1 cm gap (same area of where the springing has been noticed)

Does anyone know what the issue is? Is this just "normal" movement, or have the builders caused excessive movement by adding too much more weight to the joist with the extra moisture resistant flooring?