I have a slab of slate in front of my fireplace. Over the last six years, it has risen about a quarter of an inch above the floor. There aren't any signs of the house sagging or cracking around the mantle nor is there any signs of cracking in the mortar in the fireplace. In fact the bottom of the fireplace is still even with the slab. I can't imaging my whole house sinking, but it can't figure out what is going on. Any guesses?
It is a colonial with a basement so no moisture barrier and the flooring is standard plywood, no particle board. I'm thinking it might be moisture seeping in somewhere and causing the subfloor to swell, but it's strange that there isn't any cracking around the mortar where it meets the fireplace bottom, nor is the moulding shifted either. I can add pictures if it would help.