I agree with Tangestone. Renovation is changing the physical structure of the building, whether to repair damage or to remove, add, or move a portion of the physical structure. Redecoration changes or replaces the appearance of the surfaces of the floors, walls, or ceilings, and/or the appearance of the furnishings or fixtures, or the arrangement of the furnishings in a room.

"Renovate" generally refers to a far more complex process: tearing up the floor, pulling down walls, redoing the ceiling, etc. "Redecorate" CAN refer to a complex process, but can also refer to repainting, or getting new curtains, or hanging different pictures. Great question!