Hi, I have a subfloor (floorboards) that has a high spot in the middle that is around 15mm higher than the lowest end of the floor. Its a gradual difference. I dont want to mess around with joists. I want to raise the lower bits of the floor to the highest spot. How best to go about levelling this. Should I use shims, battens? other? Can I get battens of this size and graduated for the slope? I want to put down show hard wood Any advise gratefully received. Thanks,