The solid oak wood floor laid over 10 years ago has sprung up in the middle as it expanded to hit the walls. Have pulled up the floor and gained access under the floor boards. No leaking pipes, no obvious damp associated with the piles on which the joists are sitting but moisture meter used by a builder showed 25 - 30 (norm <10?) in the joists. No damp in walls above ground. Under floor ventilation always been clear. I need help to find the cause as builder could not see an obvious reason or source.